Manual for Diagnosis of Screw-worm Fly - xcs consulting

A Manual for the Diagnosis of 

J.P. Spradbery 

Screw-Worm Fly

A Manual 

for the Diagnosis of 

Screw-worm Fly 

J.P Spradbery 

Agriculture, Fisheries and Forestry - Australia 

1 

Agriculture, Fisheries & Forestry - AustrAliA

© Commonwealth of Australia 2002 

Reprint 2002 

ISBN 0 643 05227 5 

This work is copyright. Apart from any use as permitted under the Copyright act 1968, 

no part may be produced by any process without written permission from the Office of the Chief Veterinary 

Officer, Department of Agriculture, Fisheries and Forestry - Australia (AFFA). Requests and enquiries 

should be addressed to the General Manager, Office of the Chief Veterinary Officer, AFFA, GPO Box 858, 

Canberra, ACT, 2601, Australia. 

Authored by JP Spradbery of XCS Consulting,1991 

Design, Artwork & Printing by Expressions

Contents 


Preface i 

Foreword to the Reprint ii 

Foreword to First Print iii 

1. Introduction 1 

1.1 Geographical distribution 2 

1.2 Potential distribution of C. bezziana in Australia 2 

1.3 Australian research background 3 

2. Life Cycle 4 

2.1 Adult screw-worm fly 4 

2.2 Oviposition 6 

2.3 Incubation period 6 

2.4 Larval development 7 

2.5 Pupariation 9 

3. Description of life stages 10 

3.1 Adults 10 

3.2 Eggs 10 

3.3 Larvae 11 

3.4 Puparia (Fig. 9) 12 

4- Myiasis: Differential Diagnosis 15 

5. Flies causing myiasis 17 

6. Keys to immature stages 22 

6.1 Eggs 22 

6.2 Larvae 24 

6.3 Puparia 41 

7. Keys to adults 43 

7.1 Morphological 43 

7.2 Geographical races of Chrysomya bezziana 46 

7.3 Chemical (by Dr W.V. Brown) 48 

8. Surveillance 53 

8.1 Specimen collecting from myiases 53 

8.2 Trap (Fig. 34, Plate 8) 54 

8.3 Sentinels (Fig. 35, Plate 8) 57 

9. Acknowledgements 59 

10. References 60 

1i

A Manual for the Diagnosis of Screw-Worm Fly 

Preface 

This manual was commissioned and funded by Agriculture, Fisheries and Forestry - Australia 

as part of its Exotic Disease Preparedness Program. Its purpose is to make readily available 

a means of recognising and identifying screw-worm fly. 

Inquiries relating to this Manual should be directed to: 

Office of the Chief Veterinary Officer 


GPO Box 858 

Canberra, ACT 2601 

Foreword to the Reprint 

Since the Manual for Diagnosis of Screw-worm Fly was published ten years ago, it has been 

an invaluable aid in the identification of insects or larvae affecting animals, and on occasions 

humans. 

In 1992, the manual established its credibility when larvae from a lesion on the neck of a 

tourist returning to Australia from South America were positively identified as Cochliomyia 

hominivorax, or the New World Screw-worm fly. The availability of the manual enabled a 

rapid diagnosis, and the incident was promptly resolved. Many other suspect flies collected 

by surveillance programs and disease investigations have been quickly identified using the 

manual. Fortunately no further screw-worm flies or larvae have since been detected in 

Australia. However, in October 2001, flies from surveillance traps on the island of Boigu, far 

north Torres Strait, were suspected to be the first case of Chrysomya bezziana in Australian 

territory. Fortunately, the specimens were shown to be Chrysomya megacephala, a species 

already within Australia. Again, the manual provided the necessary information to distinguish 

the Old World Screw-worm fly from this similar species. 

Copies of the manual have been distributed throughout Australia and around the world. The 

continuing high demand for the manual led us to republish with minor amendments, to ensure 

Australia’s screw-worm fly diagnostic capabilities remain at the highest standard. 

Dr Philip Spradbery, now a private consultant in Canberra, has again prepared the amended 

text. We thank him for contributing the revisions he has personally accumulated throughout 

the years. 

Now in it’s second decade of circulation, I trust that this revised Manual for the Diagnosis of 

Screw-worm Fly will continue to serve your needs in the differentiation of screw-worm flies 

and similar insects. 

Gardner Murray 

Australian Chief Veterinary Officer and 

Executive Manager, 

Product Integrity Animal & Plant Health 


March 2002 

ii

Foreword to First Print 

The Manual for the Diagnosis of Screw-worm Fly is an integral component of the Australian 

Veterinary Emergency Plan (AUSVETPLAN). It was commissioned and funded by the 

Department of Primary Industries and Energy, through the Screw-worm Fly Management 

Committee. 

Screw-worm fly represents an important threat to Australia’s pastoral industries should this 

pest invade Australia. The most likely defence to combat screw-worm fly in Australia is the 

sterile insect release method (SIRM) which relies on overwhelming the reproductive potential 

of wild flies by the release of very large numbers of sterile flies. Matings between fertile field 

females and sterile males produce no offspring. Developed and used by the United States 

Department of Agriculture to eradicate the New World screw-worm fly from the southern 

U.S.A. and Mexico, the successful deployment of SIRM in Australia may well depend on the 

early detection and recognition of screw-worm fly on our continent. 

This manual provides the most up to date means for recognising the symptoms of 

screw-worm strike and distinguishing screw-worm fly from closely related or associated fly 

species. Some of the latest techniques in insect taxonomy have been used such as scanning 

electron microscopy (SEM) and cuticular hydrocarbon profiles. The manual is well illustrated 

with colour and black and white photographs as well as line drawings and clearly laid out 

identification keys. 

The manual is aimed at field and research veterinarians, parasitologists, quarantine 

authorities, livestock producers and diagnostic laboratories as well as for use in training 

programs and should serve its purpose well. 

The author, Dr Philip Spradbery, is one of Australia’s most experienced screw-worm fly 

specialists. He founded the CSIRO Screw-worm Fly Unit in Papua New Guinea in 1973 

and has been actively involved in screw-worm fly research for the past 18 years. With other 

colleagues from the Division of Entomology, he has evaluated SIRM Technology for the Old 

World screw-worm fly and conducted research on the mass rearing, reproductive biology, 

genetics and ecology of the screw-worm fly in South East Asia, Africa and the Middle East. 

M.J. Whitten 

Chief, 

CSIRO Division of Entomology, 

August 1991 

iii 

Agriculture, Fisheries and Forestry - Australia

1. Introduction 


Myiasis is the word used to describe an infestation of living vertebrate tissue by the larvae of 

flies (Diptera) and is derived from the greek, myia – a fly. It is a widespread condition among 

livestock and man (James 1947, Zumpt 1965). 

Myiasis has been classified according to the habits of the fly species: obligate if the larvae 

can only exist on living tissues, facultative, where larvae that normally feed on dead tissue 

develop on living tissue if the female opportunistically lays on a living host. Myiasis is also 

classified according to the site of infestation: traumatic (wound), aural, ocular, nasal and 

oral and associated sinuses, anal and vaginal, enteric etc. Some species of flies produce 

subdermal myiasis when access is via unbroken skin such as the Bot flies (Gasterophilus 

and Cuterebra spp.) and the Warble flies (Hypoderma spp.). 

There are at least 20 species of obligate myiasis-producing Diptera, more than 50 species 

which are responsible for facultative myiasis and a further 35 species recorded as accidental 

agents of myiasis (James 1947). Two of the most important of the obligate myiasis flies are 

the Old World screw-worm fly (Chrysomya bezziana) and the New World screw-worm fly 

(Cochliomyia hominivorax). 

Identification of the fly species implicated in myiasis in our region has confirmed that in most 

cases of cutaneous myiasis recorded in Africa, Arabia, India and SE Asia, the species 

involved is C. bezziana. For example, in Malaysia C. bezziana was involved in 84% and 95% 

of cattle myiases (Basset and Kadir 1982, Rajamanickam et al.1986). In Papua New Guinea 

95% of recorded myiases involved C. bezziana (Norris and Murray 1964). In India, 99% of 

myiases in cattle were due to C. bezziana (Narayan and Pillay 1936). A myiasis survey in the 

Sultanate of Oman showed that C. bezziana was implicated in 93% of myiases in goats and 

sheep. 

The New World screw-worm fly, Co. hominivorax, was formerly distributed throughout the 

southern U.S.A. and is present in Central America, the Caribbean and tropical and subtropical 

South America. During summer months, Co. hominivorax used to expand its range 

northwards, sometimes infesting up to one third of temperate continental U.S.A. (3 million 

km 2). Recent eradication programs have eliminated Co. hominivorax from the U.S.A, Mexico 

and the Caribbean Islands of Curacao, Netherlands Antilles and Puerto Rico (Graham 1985, 

Krafsur et al. 1987). Co. hominivorax was accidently introduced to Libya in 1988 (Al-Azazy 

1989, Gabaj et al.1989), and was eradicated using sterile flies from Mexico (FAO 1992). 

Co. hominivorax and C. bezziana appear to be very similar in many biological and ecological 

respects. Co. hominivorax is slightly larger than C. bezziana with smaller eggs and a higher 

fecundity (e.g. native Co. hominivorax lay 200-400 eggs per clutch compared with 190-250 

eggs in C. bezziana). Female screw-worm flies (SWF) of both species lay their eggs on the 

edge of wounds or in and around moist body orifices, the resulting larvae invade the tissues 

of the host, producing lesions which may lead to loss of condition through inappetence, 

maiming, infertility if the genitals are infested, or death (Humphrey et al. 1980). 

1


1.1 Geographical distribution 

C. bezziana occurs throughout tropical and subtropical Africa, the Indian subcontinent and 

much of southeast Asia from Taiwan in the north to New Guinea in the southeast (Norris and 

Murray 1964). Within Papua New Guinea, SWF occurs throughout the mainland to an altitude 

of 2,590m, and in New Ireland, New Britain and the offshore island of Daru in Torres Strait. 

This species does not occur in the North Solomons Province of Papua New Guinea and has 

not been recovered from any Australian islands in the Torres Strait. C. bezziana was 

accidentally introduced to Bahrain in the Persian Gulf in 1980, probably from Oman or the 

United Arab Emirates where C. bezziana is endemic, via shipments of live sheep (Kloft et al. 

1981, Rajapaksa and Spradbery 1989). In 1996, a major outbreak of C.bezziana was 

recorded in Iraq, a country in which SWF had not previously been recorded. C.bezziana has 

also been recorded in Ethiopia and is probably widespread in the Horn of Africa. 

Australia remains the only continent with a tropical climate which is free of SWF, in spite of its 

close proximity (150km across the Torres Strait) to neighbouring Indonesia and Papua New 

Guinea where SWF is endemic. The only recorded incursion took place in April 1988 when 

several adult C. bezziana were recovered from a light (electrocutor) trap aboard a livestock 

vessel in Darwin harbour (Rajapaksa and Spradbery 1989). The ship had just returned from 

offloading cattle at Brunei. 

1.2 Potential distribution of C. bezziana in Australia 

The distribution of C. bezziana and Co. hominivorax is limited primarily by the inability of SWF 

to survive cold temperatures. In Co. hominivorax adult activity decreases below 20ºC and 

where mean temperatures are 9ºC for three months or 12ºC for five months, SWF 

cannot survive (Paman 1945). Cooler temperatures result in such prolongation of the pupal 

stage that at 13ºC pupation occupies 8 weeks compared with 7 days at 28ºC. Nevertheless, 

pupae can survive brief periods at -9ºC and adults at -7ºC. 

C. bezziana adults have been recorded dispersing up to 100km (Spradbery et al, 1994) and 

Co. hominivorax up to 290km (Hightower et al. 1965). The strongly dispersive behaviour of 

adults, together with livestock movements, would probably result in rapid colonisation of 

vacant areas. 

Figure 1: CLIMEX predictions for distribution of Chrysomya bezziana in Australia. A - permanent 

colonisation, B – summer occupation. The relative climatic favourableness of each 

location is proportional to the area of the circle (from Sutherst et al. 1989). 

2

The predicted distribution of C. bezziana in Australia, using the CLIMEX computer program 

for matching climates, is illustrated in Fig. 1 for winter and summer seasons (Sutherst et al. 

1989). Large livestock rearing areas are at risk of permanent colonisation as far south as the 

mid-coast of New South Wales in average seasons. Occupation of the predicted areas would 

undoubtedly be influenced by non-climatic factors such as tree cover, host availability and 

susceptibility (=wounds). 

1.3 Australian research background 


Because of perceived dangers to the livestock industries if the Old World screw-worm fly 

became established in Australia, CSIRO Division of Entomology, with support from the 

Australian Department of Primary Industries and Energy, established a laboratory in Port 

Moresby, Papua New Guinea, in 1973. The facility was dedicated to studying the basic 

biology, physiology and ecology of Chrysomya bezziana, the Old world screw-worm fly. 

Artificial cultures were established for the first time for this species, methods were developed 

for trapping flies in the field to further population and dispersal studies, and the impact of 

gamma radiation to sterilise flies was studied to enable sterile insect release (SIRM) trials. 

In 1981, premises at Laloki on the outskirts of Port Moresby became the centre 

for mass-rearing studies. At this time a SIRM study was carried out by the ground release of 

sterile flies that resulted in 25% sterility in the local native fly population. The following year 

a major SIRM trial was carried out at Safia in the Musa Valley in which sterile flies were 

released from aircraft. The maximum sterility induced in the native Safia population was 33%. 

During a mass rearing in 1987, 18 million flies per week were produced at Laloki. 

In 1991 screw-worm fly operations in Papua New Guinea were closed down and in 1995, 

a new facility established in Malaysia at the Institute Haiwan, Kluang, Johor, under a 

memorandum of understanding between the Governments of Australia and Malaysia. 

The Malaysian program’s brief was to develop innovative mass-rearing technologies and to 

conduct a major SIRM trial to confirm that this technique is a viable eradication option for the 

Old World screw-worm fly. In a SIRM trial carried out in Malaysia in 2000, the maximum sterility 

recorded was 62%, thus confirming the validity of the sterile insect release method to 

eradicate Old World screw-worm fly. The studies at the Institute Haiwan have enabled the 

design of a large scale, 250 million sterile flies per week facility which could be constructed in 

Australia should this pest become established. 

3 

Figure 2: Larva of the Old World screwworm 

fly Chrysomya bezziana. 

Scanning electron microscope 

photograph by Helen Geier


2. Life Cycle 

(Fig. 4, Plates 1-3) 

2.1 Adult screw-worm fly 

Adult flies emerge from the soil (where the mature larvae have previously burrowed) in a 

distinct peak around dawn with 60% emerging between 0300 and 0900 hours, the 

newly-emerged flies thereby largely avoiding the deleterious effects of solar radiation and 

high daytime temperatures, and the attentions of diurnal predators at this vulnerable moment 

in their life (Spradbery et al. 1982). After a brief period (

Figure 4: Life cycle of the Old World screw-worm fly, Chrysomya bezziana. 

5 



When gravid or nearly so, female C. bezziana search for suitable hosts on which to oviposit. 

Experiments in Papua New Guinea in which radioactively labelled flies were released from 

locations 15, 25, 50 and 100km distant from traps and sentinels, labelled egg masses were 

recovered from host animals at all distances, suggesting that host-seeking behaviour may 

involve strongly dispersive activities. 

2.2 Oviposition 

C. bezziana females oviposit on the dry edges of wounds, depositing several layers of eggs 

in a compact mass cemented together in an oval plaque (Fig. 5, Plate 1). The average time 

taken to lay an egg mass is 4.1 minutes. In the hot, dry country around Port Moresby in Papua 

New Guinea, oviposition occurs in the late afternoon and evening, continuing until dusk, with 

some individuals completing oviposition in the dark (Spradbery 1979).This behaviour ensures 

that most exposed egg masses are not subject to lethal amounts of solar radiation. Second 

and subsequent egg masses can be laid at 4 day intervals (at 28ºC) with the protein 

necessary for egg development being acquired at the oviposition site when females feed 

on the wound fluids (Fig. 5) (Spradbery and Schweizer 1979). Females rarely lay more 

than two egg masses under field conditions. 

2.3 Incubation period 

Under experimental conditions, eggs of C. bezziana hatch in 10.5 hours at 37ºC, 20 hours 

at 27ºC and 50 hours at 20ºC. On host cattle, egg masses were observed to hatch between 

12 and 20 hours (mean, 15.5 hours) after they were laid. 

Figure 5: Oviposition by Chrysomya bezziana 

6

2.4 Larval development 

7 


When the eggs hatch, the first-instar larvae move from the oviposition site to the nearby 

wound where they aggregate and initially feed superficially on the wound fluids. The first 

instar occupies 24 hours after which the larvae moult into the second instar and burrow 

more deeply into the tissues of the host, with their heads buried in the wound and only the 

posterior segment with its spiracles (the external openings to the respiratory system) exposed 

(Plates 2, 3, Figs 6, 7). After a further 24 hours, the larvae moult into the final third instar 

during which most of the larval growth takes place (Fig. 8). From the second day, quantities 

of sero-sanguinous exudate (Plate 2, 3) are produced as a result of the feeding habits of the 

larvae which use their mouth hooks (Fig. 12) to tear at the host tissue and rupture the blood 

capillaries. The larvae continue their aggregative behaviour throughout larval development, 

often forming pulsating masses of hundreds or thousands tightly packed in the wound they 

have progressively enlarged (Plate 3). 

Figure 6: SWF-infested wound with second and third instar larvae of Chrysomya bezziana. 

When mature, the full-fed larvae wriggle from the wound and drop to the ground (Plate 1). 

Most larval exodus from hosts (89 per cent) occurs during the hours of darkness over a two 

day period with predominantly females 6 days and males 7 days after egg hatch (Spradbery 

et al. 1983b). Larvae falling to the ground during the night are not exposed to solar radiation 

and with surface soil temperatures comparatively low, their survival is enhanced compared 

with those experiencing conditions encountered during daylight hours in tropical climates. The 

larvae burrow 2-3 cm into the soil, turn around in the burrow they have created and prepare 

to pupate head uppermost.


Figure 7: Detail of Chrysomya bezziana third instar larvae in wound. 

Note paired spiracles (black spots) on posterior segment of larvae. 

Figure 8: Mature third instar larvae of Chrysomya bezziana (length about 15mm). 

8

2.5 Pupariation 

Within 24 hours (at 28ºC), the larva produces a puparium, a hard oval shell formed from the 

cuticle or outer skin of the larva through a process of tanning (Fig. 9, Plate 1). Within this 

protective structure, the larva changes into a pupa and finally the adult form after 7 days at 

28ºC, although the pupal stage can occupy more than a month under cool conditions. The 

developmental threshold for C. bezziana pupae is 10ºC. When mature, the adult breaks open 

the end of the puparium with its ptilinum or protrusible bladder on the head, and emerges. 

Figure 9: Puparia of Chrysomya bezziana (length about 10.0mm). 

9 



3. Description of life stages 

3.1 Adults 

Adult C. bezziana are metallic blue, bluish purple or blue/green in body colour with 

predominantly orange coloured heads and burgundy-coloured eyes (Plate 7). The hind 

margins of the abdominal tergites are black, giving the abdomen a slightly striped 

appearance which is more obvious in C. bezziana from Africa (see Fig. 31). In females the 

compound eyes are widely separated but in males, the eyes are virtually touching dorsally 

(Fig. 10). The frontal stripe of females is parallel sided and diagnostic for C. bezziana (Fig. 

10). The ovipositor and associated sclerites of C. bezziana are markedly shorter than closely 

related, similar-looking species of Chrysomya (see adult key). 

The size of adults varies, depending on the feeding regime during the larval stages. Body 

length is up to 10.0mm and head width up to 4.1mm. 

male female 

Figure 10: Head of male and female Chrysomya bezziana. Note that the compound eyes nearly 

touch in the male and both sexes have a marked “excavation” in the cheek area. 

3.2 Eggs 

The oval egg mass is brilliant white and firmly attached to the dry epidermis, or the exposed 

dermis adjacent to a wound or injury of the host animal (Plate 1). The eggs are glued to each 

other along their long axes with a dense secretion filling the spaces between the eggs which 

may be in three or more layers. The eggs are characteristically laid parallel to each other, 

giving the appearance of a shingled roof (Fig.11). The individual eggs are difficult to separate 

from an egg mass without the use of chemical solvents such as dilute potassium hydroxide 

(KOH). Egg masses contain from 95 to 245 eggs (mean, 180) although, if a female is 

disturbed while ovipositing, two or more smaller egg masses may be deposited. 

10

The egg of C. bezziana is white, 1.25mm long and 0.26mm in diameter, with a cylindrical 

shape, rounded at both ends but with one (anterior) end more tapered. Hatching lines 

enclosing a median strip occur along the entire length of the dorsal surface of the egg, 

occupying about 20-30 per cent of the width of the egg and bifurcating at the micropyle to 

produce a horse-shoe shaped structure (Fig. 11). Within the median strip, there is a plastron 

network which facilitates respiration in the developing embryo. The shell or chorion of the egg 

is comparatively thick and hard. On squeezing with forceps, the rupturing of the chorion is 

quite audible. 

Figure 11: Egg mass and egg of Chrysomya bezziana. 

3.3 Larvae 


There are three instars during development of C. bezziana larvae. The first two instars each 

occupy one day and the third and final instar lasts three to five days. They have been 

described by Kitching (1976). There are 12 visible segments: the head, three thoracic and 

eight abdominal segments. The posterior spiracles of first, second and third instar larvae 

each have one, two or three openings respectively to the tracheal system (Fig. 12). 

First Instar (Figs. 12,13) 

The first instar larva is white, 1.6mm long and 0.25mm in diameter, round in cross section, 

without obvious protuberances or papillae, and with bands of spines on most of the body 

segments. The spines are thornlike, black in colour and backwardly directed. The prothoracic 

spiracle is a small, simple opening. There is a pair of posterior spiracles each with a single 

opening but with no peritreme. 

Second Instar (Figs. 12,13) 

Second instar larvae are white to cream coloured, 3.5-5.5mm long and 0.5-0.75mm in 

diameter. Spines in bands, thornlike, black, directed backwards, all with a single point. 

Protharacic spiracles are non-functioning (occluded) with 4-5 stubby, lightly sclerotised 

papillae or branches. Each of the pair of posterior spiracles is surrounded by a heavily 

sclerotised peritreme, dark brown to blackish in colour, which is incomplete or nearly so 

dorsally and ventrally, and has 2 slit-like spiracular openings. 

11


Third Instar (Figs. 12,17) 

Third instar larvae are 6.1-15.7mm long and 1.1-3.6mm in diameter. Young third instar larvae 

are whitish to cream coloured with mature larvae developing a pinkish colouration. The heavy 

bands of dark, robust, thornlike spines are very prominent. The anterior spiracles are nonfunctioning 

(occluded) with 4-6 lightly sclerotised (pale brown) papillae or branches. The 

posterior spiracles are each surrounded by a heavily sclerotised peritreme (dark brown to 

blackish) which is incomplete ventrally, and with 3 slit-like spiracular openings at 

approximately 45º to the horizontal. 

3.4 Puparia (Fig. 9) 

The mature larva, after burrowing into the soil, undergoes a process of pupariation during 

which the cuticle of the larva becomes heavily sclerotised. In the early stages of pupariation, 

the larva contracts its longitudinal musculature thereby shaping the puparium. The colour 

changes from deep pink, through brown and finally to almost blackish brown as sclerotisation 

is completed. The ends of the puparium are rounded with the anterior end a little more 

pointed. Some of the characters observed on the cuticle of the third instar larvae, especially 

the bands of spines, are retained in the surface structure of the puparium. 

The puparium is up to 10.1mm in length and 3.6mm in diameter. 

12

Figure 12: Details of larval morphology in Chrysomya bezziana. 

13 



Figure 13: First and second instar larvae of Chrysomya bezziana. 

14

4- Myiasis: Differential Diagnosis 

(Plates 2-6) 

Although the end results of unrestricted oviposition by SWF are spectacular, this cannot be 

said of more recently established myiases, which may be insidious and readily overlooked, 

even following close examination (see Fig. 33). This is particularly important in relation to 

quarantine and the detection of invasion into hitherto uninfested areas, and should be drawn 

to the attention of all people in Australia associated with livestock, including graziers, animal 

health officers and veterinarians. At the quarantine level, infestation by C. bezziana may not 

be evident initially in epizootic proportions, as the term ‘exotic disease’ might be taken to 

imply. 

The clinical syndrome, pathogenesis, pathology and differential diagnosis of C. bezziana 

infestations have been studied and described by Humphrey et al. (1980) and Spradbery and 

Humphrey (1988). 

Predisposing conditions 

Infestations are generally associated with traumatic injury, erosive or ulcerative lesions or 

haemorrhage. Differences in occurrence and site of myiasis between animal species probably 

reflect behavioural, environmental and husbandry factors rather than innate differences in 

susceptibility. 

Infestation commonly follows parturition. The navel of the new born and the vulval or 

perineal region of the dam, particularly when traumatised, are principal sites of infestation. 

Husbandry procedures such as dehorning, castration, branding, docking and ear tagging are 

also common sites of infestation. Myiasis associated with otitis externa has been seen in 

dogs, and myiasis associated with foot abscess has been seen in sheep and cattle. In 

Australia, the technique of ‘mulesing’ sheep would provide an ideal medium for screw-worm 

fly myiasis. Traumatic injuries due to barbed wire or other penetrating objects are also 

commonly infested. Skin punctures caused by cattle tick and the lesions associated with 

buffalo fly infestations are attractive to screw-worm fly and provide ideal sites for myiasis 

in areas of Australia where the screw-worm fly would be expected to survive throughout the 

year. A particularly important feature of the disease in sheep, with major consequences for 

the Australian sheep industry, is the ability of C. bezziana to invade the intact perineal region 

of ewes in the absence of overt trauma or haemorrhage (Plate 5). 

Course of myiasis 


Myiasis by C. bezziana begins with the early larval invasion of the disrupted epidermis, 

where the larvae aggregate in small cavities up to 5-10mm in diameter. There the larvae 

are bathed in small quantities of serous fluid and are visibly active. Within 24 hours, the 

cavities enlarge and extend laterally and deeply into the subcutaneous tissue and muscle. A 

sero-sanguinous exudate is evident at this stage. Progressive liquefactive necrosis of muscle 

and skin continues, associated with larval growth and invasion until a large cavernous lesion 

with irregular ragged edges is present. The depths of the lesion contain a seething, pulsating 

mass of larvae immersed in copious quantities of necrotic, fibrino-purulent or liquefied tissue 

and blood (see wound biopsy, Plate 4). Haemorrhage from the lesion may be severe and the 

15


surrounding tissue is tense, oedematous and hot to the touch. Lesions emit a characteristic 

pungent sickly odour. By days 6-7, in uncomplicated cases, mature larvae may be seen 

actively migrating from lesions and recovery occurs in otherwise healthy animals, with fibrous 

granulation tissue growing beneath the affected areas, with incipient muscle and epithelial 

regeneration (Plate 4). 

Clinical syndrome and pathology 

Before the occurrence of major functional disturbance or disease associated with extension 

of the lesion, signs of infestation include the presence of a ragged, foul-smelling lesion 

containing C. bezziana larvae, constant licking of the lesion by the host and an initial 

hypersensitivity followed by apparent decreased sensitivity of the lesion, host restlessness, 

lethargy, inappetence, debilitation, decreased growth rate, anaemia and hypoproteinaemia. 

Clinically, intermittent irritation and pyrexia are present. A cavernous lesion of varying size 

from 1-2cm to in excess of 15-20cm diameter which, in uncomplicated cases, undergoes 

fibrous involution subsequent to larval exodus. Histologically, two distinct phases are evident: 

a phase of necrosis, intense neutrophil infiltration, and haemorrhage associated with tissue 

invasion and growth of larvae; and a fibroplastic, healing phase in which mast cells and 

eosinophils are prominent. Significant haematological and biochemical changes include an 

initial neutrophilia, anaemia, and decreased total serum protein with a progressive rise in 

serum globulins. A significant loss in body weight can occur in infested animals. Extension of 

the lesion into body cavities is a common sequel. Peritonitis following navel infestation, sinusitis 

following dehorning and pleuritis following thoracic infestation occur. Functional 

disturbances, particularly those associated with infestations of the muscles responsible for 

locomotion also occur. 

Although mild lesions and even severe ones will resolve once vacated by larvae, lesions 

caused by C. bezziana become particularly attractive to further infestation by gravid female 

flies. Ultimately, massive invasion of the affected area by larvae, with extensive necrosis of 

muscle tissue and overlying skin can occur, resulting in severe clinical disease, debility and 

even death. 

Detection and diagnosis 

Myiasis due to screw-worm fly must be distinguished from myiasis due to the larvae of 

carrion ‘blowflies’. In the case of myiasis of sheep by the Australian sheep blowfly, Lucilia 

cuprina, the larvae feed rather superficially on the surface of the wound, being sustained by 

the flow of serous exudate from the host (Plate 6). If disturbed, L. cuprina larvae rapidly 

evacuate the site of the wound, burrowing into the surrounding wool (Plate 6). In C. bezziana 

myiases, disturbed larvae retract deeper into the wound and are difficult to remove, even 

with forceps (Plates 2, 3). Any ulcerative or erosive lesions, especially following invasive 

husbandry procedures or trauma, should be investigated with a view to the possibility of their 

being the site of screw-worm fly infestation. Diagnosis of screw-worm infestation is usually 

made by detection of larvae in lesions and recognising the characteristic smell of the lesions. 

For confirmation larvae should be collected in 80% alcohol and submitted for laboratory 

examination (see Surveillance section 8). 

16

5. Flies causing myiasis 

The following lists those flies most likely to be encountered in cases of myiasis plus closely 

related or similar looking species, with special reference to SWF myiasis. Distribution maps 

for most species are given in Fig. 14. 

Chrysomya bezziana – Old World screw-worm fly 

Obligatory myiasis fly (primary screw-worm). Serious parasite of man and warm-blooded 

animals throughout the tropical and sub-tropical Old World. 

Cochliomyia hominivorax – New World screw-worm fly 

Eradicated from southern states of U.S.A. and Mexico but still present in Panama and 

northern areas of South America and most of the Caribbean. Accidentally introduced to Libya 

in North Africa in 1988. The subject of continuing eradication programs in Central America 

using sterile flies bred at the Mexican-American Commission for the Eradication of Screwworms 

facility at Tuxtla Gutiérrez, Mexico. The facility was established in 1976 with a capacity 

of up to 500 million flies per week. 

Chrysomya megacephala – Oriental Latrine fly 

Very common species. Adults superficially similar to C. bezziana but generally a larger-sized 

species. The larvae breed in carrion or dead, decomposing tissues, very rarely found in 

C. bezziana-infested myiasis although adults frequently feed at such wounds. Common 

around human habitation. From its origins in New Guinea and the nearby Pacific islands, 

C. megacephala is now widespread throughout India and SE Asia with many recent 

introductions as far afield as South America, Africa and Japan. 

Chrysomya saffranea – Steelblue blowfly 

A New Guinea/Australia blowfly species occasionally found breeding in the necrotic tissue 

associated with C. bezziana myiasis but normally breeding on carrion. Adults superficially 

similar to C. bezziana and very similar to C. megacephala. C. saffranea has been recovered 

from cattle myiases in tropical Australia. 

Cochliomyia macellaria – Secondary screw-worm fly 

C. macellaria is the New World equivalent of C. saffranea in its bionomics. It is a carrion 

breeder but occasionally found associated with Co. hominivorax myiases as a secondary 

invader. The adults are superficially similar to Co. hominivorax with which it was 

taxonomically confused until 1933. 

Chrysomya rufifacies – Hairy Maggot blowfly 

One of a guild of Australian blowflies which occur on sheep. The adults are a metallic green. 

The larva, like C. albiceps, has fleshy protuberances (papillae) giving it a hairy appearance. 

A secondary blowfly on sheep where its larvae may be predatory on primary blowfly larvae 

although large infestations of C. rufifacies can cause the death of a sheep in a short time. 

Occasionally, its larvae are associated with C. bezziana myiases. Accidentally introduced to 

southern U.S.A., Central and South America. 

Chrysomya varipes – Small Hairy Maggot blowfly 

A small species occasionally identified from sheep myiases in Australia. 


Chrysomya albiceps – Banded blowfly 

Very similar to C. rufifacies adults and with a hairy maggot type but found in Africa, Europe, 

Arabia and India. Recently introduced to Central and South America and the Caribbean. It 

is one of the important blowflies of sheep in South Africa but its larval biology seems to be 

similar to the secondary C. rufifacies and it is classed as mainly a scavenger species. 

17


Calliphora stygia – Brown blowfly 

One of several Calliphora species implicated in myiasis of sheep in Australia, the others 

include C. albifrontalis (West Australian Brown blowfly), C. augur, C. hilli, C. varifrons and 

C. dubia (=nociva) (Lesser Brown blowfly). The Australian Calliphora spp. adults are 

non-metallic in colour, most being blackish grey to golden and yellowish brown and readily 

distinguished from the metallic blue to green of the remaining calliphorid blowfly species. 

Australophyra rostrata – Black Carrion fly 

A member of the family Muscidae. Adults are dark metallic blue about 5-6mm long. Often 

infests scabs of partially healed myiases on sheep. Occurs throughout Australia during 

summer-autumn period. 

Lucilia cuprina – Australian Sheep blowfly 

In North America this species is known as Phaenicia cuprina. Two sub-species are 

recognised (L.c. cuprina and L.c. dorsalis). L. cuprina was introduced into Australia perhaps 

from South Africa towards the end of the last century. It is the major myiasis species on 

sheep causing an estimated loss of $150 million per year. It is also of economic importance 

in South Africa and recently has been detected in New Zealand. A primary myiasis species, 

L. cuprina is probably responsible for initiating infestations that are subsequently exploited by 

other blowfly species. 

Under most conditions it survives poorly in carrion and its persistence is largely linked to its 

ability to infest sheep although such myiases may not be evident to the casual observer. 

So-called ‘covert strikes’ may consist of small myiases on the breech, pizzle or footrot lesions 

that do not expand to the full-blown myiases seen on the breech, back or body normally 

considered to characterise sheep myiases. The effects of Lucilia cuprina are most obvious 

and damaging in so-called ‘fly-waves’ when sustained periods of wet weather produce 

‘fleece-rot’ due to bacterial growth and a large proportion of a flock can exhibit body myiasis. 

Several L. cuprina infestations of man have been recorded in Australia and elsewhere. 

Lucilia sericata – English Sheep blowfly 

A widespread species which generally breeds in carrion or garbage but is an important 

myiasis species of sheep in the United Kingdom, South Africa and New Zealand. 

Sarcophagidae 

Includes the familiar greyish checkerboard patterned ‘flesh flies’. Typically viviparous, females 

deposit first instar larvae on decaying animal or vegetable matter, snails, insects, etc. Rarely 

involved in myiasis in Australia although species of Wohlfahrtia are of considerable medical 

and veterinary importance overseas. 

Wohlfahrtia magnifica – Wohlfahrt’s Wound Myiasis fly 

Member of the family Sarcophagidae. Females deposit larvae. W. magnifica is the most 

important primary (obligatory) myiasis species in Europe, Russia, Asia Minor and North 

Africa. Damage to hosts is very rapid due to the larviposition habit, rapid growth and large 

numbers of larvae deposited by the female. Frequently infests man. 

Wohlfahrtia nuba – Chequerspot fly 

Distributed further south than W. magnifica, this secondary-myiasis species is generally found 

infesting diseased tissue of camels, sheep, goats and occasionally man. Common in feedlots 

of the Arabian peninsula, particularly on imported sheep. 

Since the first publication of this Manual, some additional species of insects associated with 

cutaneous myiasis and/or screw-worm fly rearing warrant mention. 

18


Dermatobia hominis – Human Bot Fly or Tropical Warble fly 

Larvae of this myiasis fly have been recorded on several occasions infesting Travellers 

returning from Central or South America. 

Cordylobia anthrophaga - Tumbu Fly or Human Warble fly 

This African species is another potential introduction to Australia, although not yet recorded 

here. 

Hypoderma bovis and H. lineatum - Cattle Warble flies 

Cattle warble flies do not occur in Australia but infested cattle have been imported and 

diagnosed during quarantine. The adult fly is hairy, about the size of a bee, with a yellow-toorange 

abdomen. The mature larvae are up to 20mm in length and cause characteristic and 

unique lesions, or warbles, which are generally found along the back of host cattle. Warble 

flies cause considerable loss to cattle industries in the Northern Hemisphere through damage 

to hides and decreased production of meat and milk. The species has been recorded in man. 

The Bot or Warble fly infestation is characterised by the mature larva, having migrated to just 

below the skin of its host, piercing a small breathing hole and becoming enclosed in a cyst, 

thus forming a prominent swelling (or ‘warble’) below the skin. 

Tunga penetrans – Sandflea 

There have been cases of the Sandflea (Tunga penetrans) entering Australia in returning 

travellers (Spradbery et al. 1994). Originally endemic to South America, this pest has spread 

to India, U.S.A. and Africa. Female fleas flourish in sandy soil, dust and animal pens and 

attach themselves to a passing host and penetrate the skin. The flea then grows to about 

1cm as eggs develop in its body cavity, causing great pain and an ulcerated lesion. The flea 

pierces the skin to enable respiration and expel from 200 to several thousand eggs. In 

humans the infestations are generally found in the feet. 

Chrysomya nigripes 

A carrion-breeding fly species whose larvae have been found on vats used for artificially 

rearing C. bezziana in Papua New Guinea. The larvae are very characteristic, with narrow 

rings of spines around each segment and a prominent black plate-like band (sclerotisation) 

on the dorso-lateral surface of each segment. 

19


Figure 14: Geographical distribution of several species causing or associated with myiasis 

of livestock and humans. 

20

21 


Figure 14 (Contd): Geographical distribution of several species causing or associated with myiasis 

of livestock and humans.


6 – Keys to immature stages 

The keys include only those species causing or closely associated with myiasis and presume 

that the material for diagnosis was obtained from live or very recently dead hosts. 

Any material keying out to either of the two SWF species should be confirmed by specialists 

at the Australian National Insect Collection (ANIC), CSIRO Division of Entomology, Canberra, 

ACT 2601; Fax (02) 6246 4000. 

6.1 Eggs 

Eggs and egg masses can often be identified to species or species group level using the 

following characters; colour, size (length and diameter), relative length and width of the 

hatching lines with their enclosed median strip, and the shape of the strip at the anterior, 

micropylar end (Figs 11, 15) (Kitching 1976, Erzinçlioglu 1989). 

1. Median strip occupies 20-30% of the diameter and almost the full length of the egg 

including anterior and posterior poles, eggs laid parallel and firmly attached to each 

other and the oviposition substrate, white or whitish, small (

Figure 15: Eggs of several species of Calliphoriadae associated with wound myiases. 

Note: each set of prints is at the same scale. 

23 



6.2 Larvae 

Because the first two larval instars are relatively inconspicuous and occupy only two days 

of the 4-7 day larval development period, they are very rarely presented for diagnosis, and 

so the larval separation key is confined to the third (final) instar larva (Fig. 16). Reference 

to figures in key refers to scanning electron microscope photographs of mature larvae (Figs 

18-28). 

For further details of some of the larvae described in this key and other closely related species, 

see Erzinçlioglu (1987), Fuller (1932), Kitching (1976) and Liu and Greenberg (1989). 

1. Body with prominent projections of papillae on each segment (= ‘hairy maggot’) (A) 

………………...............................................................................................................…2 

- Body without prominent papillae except few on posterior segment (’smooth maggot’) 

(B) ………………..................................................................................................………4 

2. Very ‘hairy’ maggot, large larva (up to 17mm long); papillae present on both dorsal 

and ventral surfaces …………………..................................................…………………..3 

- Less ‘hairy’ maggot, small larva (


5. Powerful mouth hooks, robust larva extensively covered in black thorn-like spines, 

anterior spiracles with 5+1 lobes (Fig. 26) ………………….……...Wohlfahrtia magnifica 

_ 

- Less robust larva without thorn-like spines ………………………....other Sarcophagidae 

6. Posterior spiracle with peritreme complete (closed) or peritreme indistinct, button 

within peritreme (G) ………….......................................................................……………7 

- Peritreme open, button indistinct and in open area of peritreme (H) …………..…….. 10 

7. Respiratory slits of posterior spiracles kidney shaped or very sinuous (G) ………….. 

...........................................................................................................................Muscidae 

- Respiratory slits of posterior spiracles straight and roughly parallel (see H) …………..8 

8. Accessory oral sclerite present between mouth hooks (I) (Fig. 28) …….............………. 

..................................................................................................................Calliphora spp. 

- No accessory oral sclerite (J)..........................................................................................9 

9. Posterior spiracles round, small, peritreme thick and wide, slits short and wide (K), 

concentration of black spines above anus (Fig. 27)..................................Lucilia cuprina 

- Posterior spiracles pear-shaped (length greater than width), peritreme thinner and 

narrower, slits longer and thinner (L), very few black spines above anus (Fig. 27)......... 

...............................................................................................…………….Lucilia sericata 

25


10. Tracheal trunks from posterior spiracles up to segment 9 or 10 heavily pigmented (M), 

anterior spiracle with 7-12 papillae (Fig. 19) …………......…....Cochliomyia hominivorax 

(N.B. It may be necessary to dissect preserved specimens to display tracheal trunks) 

- Tracheal trunks not heavily pigmented …….......................................………………….11 

11. Posterior margin of segment 11 without dorsal spines (N) (Fig. 22) ……………............. 

....................................................................................................Cochliomyia macellaria 

- Posterior margin of segment 11 with dorsal spines (O) …………………..............……12 

12. Bands of black spines, thornlike with single teeth, not forming files (P), anterior 

spiracle with 4-6 papillae (Q) (Fig. 18) ………………………….......Chrysomya bezziana 

- Bands of pale brown to dark brown spines with 1 or 2 or more teeth, occurring singly 

or in files (R), anterior spiracles with 10 or more papillae (S)…...........………………..13 

13. Spine bands composed of elongate bifid or trifid spines anteriorly, tending to become 

single pointed and posteriorly, whole band grading laterally into sharp thorn-like 

spines; posterior sub-spiracular area bare, anal protuberance with short files of setae 

along its posterior surface (T); anterior spiracles with about 10 papillae (Fig. 20)........... 

..............................................................................………………….Chrysomya saffranea 

- Spine bands sparse having short blunt, simple spines mostly tending to form files of 

2-5, some elongate, bifid structures present in lateral regions; posterior sub-spiracular 

region densely setulose, setae forming distinct polygonal blocks which extend down 

posterior surface of anal protuberance (U); anterior spiracles with about 13 papillae 

(Fig. 21).……………….........................................................….Chrysomya megacephala 

26


Figure 16: Illustrated key to species of final instar fly larvae associated with wound myiases. 

27


Figure 17: Morphology of third instar larvae. 

28

Figure 17 (contd): Morphology of third instar larvae. 

29 



Figure 18: Chrysomya bezziana third instar larva. 

30

Figure 19: Cochliomyia hominivorax third instar larva. 

31 



Figure 20: Chrysomya saffranea third instar larva. 

32

Figure 21: Chrysomya megacephala third instar larva. 

33 



Figure 22: Cochliomyia macellaria third instar larva. 

34

Figure 23: Chrysomya rufifacies third instar larva. 

35 



Figure 24: Chrysomya albiceps third instar larva. 

36

Figure 25: Chrysomya varipes third instar larva. 

Figure 25: Chrysomya varipes third instar larva. 

37 



Figure 26: Wohlfahrtia species third instar larva. 

Figure 26: Wohlfahrtia species third instar larva. 

38

Figure 27: Lucilia species third instar larva. 

Figure 27: Lucilia species third instar larva. 

39 



Figure 28: Calliphora stygia third instar larva. 

40

6.3 Puparia 


Although puparia are rarely presented for identification, they retain many of the characters 

of the final instar larva and thus provide useful material for diagnosis. The barrel shaped 

puparium is reddish brown to almost black in colour. The most obvious features are the 

bands of spines and the non-functional anterior and posterior larval spiracles. In C. albiceps, 

C. rufifacies and C. varipes, and ‘hairy maggots’, the fleshy papillae of the larva are 

consolidated into the puparium as pointed projections and knobs. 

The functional respiratory system of puparia consists of a pair of pupal respiratory horns, 

tube-like structures on the dorsolateral surface of the fifth segment. Early puparia have a 

‘bubble membrane’ consisting of many globules which is ruptured by the horns as they evert 

(Fig. 29). 

Figure 29 illustrates, with scanning electron microscope (SEM) photographs, the two screwworm 

species and several associated calliphorid puparia. This figure together with the larval 

keys will facilitate identification of puparia (see also Kitching 1976, Liu and Greenberg 1989). 

Figure 29: Details of puparia of several species of Calliphoridae associated with myiases. 

41


Figure 29 (contd): Details of puparia of several species of Calliphoridae associated with myiases. 

42

7. Keys to adults 

7.1 Morphological 

43 


1. Meropleuron ( =hypopleuron) usually with no bristles but if present, very weak............... 

………................................................................................................................Muscidae 

- Meropleuron with prominent bristles present (A) …….....................….........................2a 

2a. Subscutellum distinct, convex; artista of antenna often bare..........................Tachinidae 

Subscutellum not developed; arista usually plumose...................................................2b 

2b. Colour non-metallic, predominantly grey with black spots of checkerboard pattern on 

abdomen; three black longitudinal stripes on thorax (B) (Sarcophagidae) ………..……3 

- Colour metallic blue or green or robust yellow to brown flies (Calliphoridae) ……….…4 

3. Arista of antenna bare or with short hairs (C); grey abdomen with black spots (E)......... 

…….................................................................................................…….Wohlfahrtia spp. 

- Arista of antenna with medium to long hairs (D); abdomen with grey/black 

checkerboard pattern (F) ………………………............................... other Sarcophagidae 

4. Base of stem vein dorsally with row of bristles (G) (Chrysomyinae) …………..........….5 

- Base of stem vein without bristles (Calliphorinae) ……………..............................……12 

humerus / 

pronotum 

mestonotum 

greater ampulla 

tergum 

sternum


5. Lower (posterior) squamae covered with fine hairs above (H); no longitudinal stripes 

on thorax (Chrysomya spp.) ………………................................................................….6 

- Lower squamae without hairs except near base (I); thorax with three longitudinal 

stripes ( =vittae) (Q,R) (Cochliomyia spp.)......................................................................9 

6. Anterior spiracle (A) dark, blackish, blackish-brown or at least dark orange …....……..7 

- Anterior spiracle pale yellow, creamy or white ……………....................................……10 

7. Lower (posterior) squamae waxy white; frontal stripe of female parallel sided (J); 

ovipositor relatively short (L); facets of male eye scarcely enlarged above and not 

sharply demarcated from area of slightly smaller facets below (Fig. 10); moderate to 

deep indentation in cheek of male and female (Fig. 10, J) ………Chrysomya bezziana 

- Lower squamae blackish brown to dirty grey; frontal stripe of female broader in middle, 

not parallel sided (K); ovipositor relatively long (M); no marked indentation in cheek (K) 

.........................................................................................................................…………8 

8. Setulae around vibrissae on face and parafacial with at least several, usually many, 

black ones (N); facets of male eye much enlarged above and sharply demarcated 

from area of smaller facets below (O) …….........................….Chrysomya megacephala 

- Setulae around vibrissae not black or, rarely, two or three black ones present; facets 

of eye of male larger above than below but without any distinct line of demarcation (P) 

.................………............................................................................Chrysomya saffranea 

44 

frons 

gena

45 


9. Central stripe on thorax only just extending forward of mesonotal suture (Q); 

fronto-orbital plates ( =parafacialia) of head with black setulae (S); fifth ( =fourth visible) 

segment of abdominal tergite usually with only very slight dusting laterally; in females, 

basicostal scale (T) dark brown to almost black.......................Cochliomyia hominivorax 

- Central stripe on thorax extending well forward of mesonotal suture (R); fronto-orbital 

plates with only yellow hairs (but their insertions appear as black dots); fifth (fourth 

visible) abdominal tergite with dense white dusting laterally ( =white spots); in females, 

basicostal scale is yellow………...........................................……Cochliomyia macellaria 

10. Proepisternal seta (stigmatic bristle) present (U) ………..................................……….11 

- Proepisternal seta absent (V) ……………........................................Chrysomya albiceps 

11. Species large (7mm long); face and cheeks with dense silvery hairs on dark brown to 

black surface....................................................................………….Chrysomya rufifacies 

- Species small (5-6mm long); face and cheeks wholly yellow; male front femur with 

prominent, long white hairs ………….................................................Chrysomya varipes 

12. Body deep metallic blue to blue-black or yellow to brown; larger species (8-10mm 

long)……………........................................................................................Calliphora spp. 

- Body metallic green or coppery green; small to medium-size flies (


7.2 Geographical races of Chrysomya bezziana 

Collections of the Old World screw-worm fly, Chrysomya bezziana, from different parts of its 

geographical range have shown morphological differences between populations from southeast 

Asia, Arabia and Africa (D.H. Colless, personal communication) (Figs 30, 31). 

Figure 30: Wings of Chrysomya bezziana 

from different geographical regions. 

46 

• body colour is mainly blue/black in SE 

Asia specimens; blue/green in Arabian and 

green/blue in African with the black 

abdominal bands more obscure in SE Asian 

and more obvious in African flies. 

• wing base (A) of SE Asian flies is slightly 

blackened with cell R clear, almost 

completely clear in Arabian but strongly 

blackened, especially cell R, in African flies. 

• soft hairs of the thorax (pleura) (B) are 

predominantly black in SE Asian, pale in 

Arabian and mixed in African flies. 

• lower (posterior) squamae (C) of SE 

Asian flies darker waxy white and covered 

in long black hairs; African and Arabian flies 

with more brilliantly white lower squamae 

and long white hairs. 

• frontal setulae (bristles) (D) in SE Asian 

flies black; pale except for dorsal patch in 

Arabian flies and lower 2/3 mixed black and 

pale (gingery) in African flies. 

• setulae around vibrissa (E) in SE Asian 

flies, a few black below vibrissae in Arabian 

flies and all pale in African flies. 

• genal groove below compound eye (F) 

heavily indented in SE Asian flies, less so in 

Arabian and only slight indentation in 

African flies.


Figure 31: Morphological differences between geographical races of Chrysomya bezziana. 

47


7.3 Chemical (by Dr W.V. Brown) 

Introduction 

Many diagnostic laboratories, universities and research institutes operate a gas 

chromatograph for analytical studies. The gas chromatograph can be used to detect 

chemical differences between different insect species. 

The surface lipids (hydrocarbons) on the cuticle of insects protects them against 

dessication and invasion of pathogenic organisms and harmful substances. The chemical 

characterisation and quantification of hydrocarbons in insects has shown that they can be 

a useful chemotaxonomic character. They have been used to distinguish otherwise 

morphologically identical species and even sub-species and geographical races of the same 

species. Profiles can be generated from parts of a single fly (e.g. thorax alone). C. bezziana 

and C. hominivorax adults can be readily distinguished and separated from morphologically 

similar blowflies associated with the two SWF species, using cuticular hydrocarbon profiles 

(Fig. 32). Nevertheless, differences in hydrocarbon profiles within a species do occur (due to 

age and sex) and, as with every other taxonomic character, care must be exercised in 

interpreting results (Brown, et al. 1998). 

Preparation of samples 

Individual flies (or parts thereof) are put in small test tubes and just covered with hexane 

(liquid chromatography grade). After ten minutes the hexane is removed and introduced to 

the top of a 5cm column of Bio-sil A (100-200 mesh, Bio-Rad) in a pasteur pipette. The 

extraction is repeated 3 times. The hydrocarbons are then eluted with a further 2-3ml of 

hexane. The solvent is removed at room temperature under a stream of nitrogen. Hexane 

(50 µl) is then added and ca 2 µl of the resulting solution injected for gas chromatography. 

Unsaturates can be detected readily by treatment of a sample with a little bromine followed 

by rechromatography with any alkenes selectively removed. 

Gas chromatography 

At CSIRO Division of Entomology, gas chromatography (GC) is performed on a Varian model 

3300 capillary gas chromatograph filled with a cool on-column injector and a flame ionisation 

detector. The data system used is an Epson PCe computer with an AD converter and Data 

Acquisition, Plotting and Analysis software. The column is a DB1 bonded phase methyl 

silicone column (30m x 0.32mm, film thickness 0.25µm, J&W Scientific). Injection is done at 

60º, the temperature is then raised rapidly to 220º followed by programming at 4º/min to 310º 

with a hold at this temperature for 15min. Helium (1.5ml/min) is the carrier gas. 

Mass spectrometry 

Mass spectra are determined on a VG Micromass 70-70F mass spectrometer interfaced 

directly to a Hewlett-Packard 5792A capillary gas chromatograph and a VG 11-250 data 

system. GC conditions are similar to those above. Electron ionisation mass spectra are 

obtained at an ionisation voltage of 70eV and a source temperature of 200º. The mass 

spectra in conjunction with GC retention data (equivalent chain length, ECL) are used to 

determine the chemical identity of the individual hydrocarbons (Lockey, 1988). 

48

Hydrocarbon content (Table 1) 

Chrysomya bezziana 

The cuticular hydrocarbons of newly emerged C. bezziana comprise mainly saturates with 

carbon chain lengths of ca 25 to 37. The largest components are 2-methyloctacosane (ECL= 

28.64); internal-methylnonacosane (i-methylnonacosane, 29.33); 2-methyltriacontane (30.64); 

i-methylhentriacontane (31.31); and i-methyl- and dimethyl-tritricontane (33.31 and 33.57). 

Males and females have identical profiles. Between emergence and day 5, quantitative 

changes in cuticular hydrocarbon composition occur; these are more pronounced for females 

than males. From day 5 the profiles stabilise again. The percentages of several components, 

mainly those with carbon chain lengths greater than 34, increase while those of other 

components decrease. Values for major components are given in the Table for newlyemerged 

and 5 day old flies. Flies of intermediate ages have hydrocarbon compositions 

between those of these two stages. 

Chrysomya megacephala 

Young C. megacephala flies also contain hydrocarbons which are predominantly alkanes, 

but mainly of shorter chain lengths than those of C. bezziana. The two largest components 

are i-methylheptacosane (27.33) and 2-methyloctacosane (28.64). Other major components 

include n-heptacosane (27.00), n-nonacosane (29.00) and i-methylnonacosane (29.33). The 

most abundant alkanes are heptacosene and nonacosene (26.79 and 28.81, 2-3%). Cuticular 

hydrocarbon data for older flies are not available. 

Chrysomya saffranea 

C. saffranea contains hydrocarbons very similar to those of C. megacephala. The mean 

value of heptacosene (26.79) in females is higher, but this component is very variable and 

some individuals have levels comparable with those of C. megacephala. Again cuticular 

hydrocarbon data for older flies are not available. 

Cochliomyia hominivorax 


The cuticular hydrocarbons of newly-emerged male and female Co. hominivorax are 

dominated by those with a C29 carbon chain, particularly i-methylnonacosane (29.33). 

2-methyloctacosane (28.64) is also abundant but all other components are quite minor. 

The hydrocarbon composition of this species changes much more with age and sex than 

does that of C. bezziana (see Pomonis 1989). By day 5, males have aquired large quantities 

of n- and i-methylpentacosane and heptacosane and have lost most of the i-methyl- and 

3-methylnonacosane. Females also acquire n- and i-methylheptacosane (but not 

pentacosane) as well as increasing the proportions of longer chain length material (greater 

than C30). 

49


TABLE 1. DIAGnOSTIC CuTICuLAR HyDROCARBOn PEAKS FOR Chrysomya AnD CoChliomyia SPECIES 

C. bezziana C. megacephala C. saffranea Co. hominivorax Co. macellaria 

Compound1 ECL2 Male Female Male Female Male Female Male Female Female 

% % % % % % % % % % % % % 

n-C25 25.00 2.1 (0.7) 1.9 (0.5) 0.4 0.3 0.2 0.4 0.9 (9.6) 0.4 (2.1) 0.5 

i-MeC25 25.37 0.2 (0.7) 0.2 (0.2) 0.8 1.3 0.7 1.3 0.4 (20.2) 0.0 (0.0) 1.5 

2-MeC26 26.64 0.8 (1.5) 0.9 (0.6) 4.2 5.2 4.7 5.3 0.4 (0.0) 0.2 (0.0) 0.6 

C27:1 26.79 1.2 (1.1) 1.1 (0.4) 1.8 3.6 3.4 7.7 0.1 (0.0) 0.0 (0.0) 0.0 

n-C27 27.00 4.0 (2.2) 3.6 (2.0) 8.3 8.5 6.6 8.5 2.7 (12.0) 1.4 (8.1) 13.8 

i-MeC27 27.33 1.1 (1.8) 1.0 (0.8) 18.6 19.4 17.8 17.6 2.5 (6.9) 0.9 (6.8) 20.7 

5-MeC27 27.51 0.2 (0.2) 0.2 (0.1) 0.3 0.3 0.3 0.3 0.2 (0.0) 0.1 (0.0) 3.4 

diMeC27 27.64 0.1 (0.3) 0.1 (0.1) 4.9 3.8 4.7 3.4 1.4 (0.0) 0.5 (1.4) 5.4 

3-MeC27 27.75 2.2 (0.5) 1.9 (0.5) 0.8 0.7 0.7 0.7 2.0 (4.0) 1.5 (2.7) 12.8 

2-MeC28 28.64 6.8 (7.8) 6.9 (3.2) 15.2 14.8 14.7 12.3 8.7 (1.6) 9.4 (2.1) 1.7 

n-C29 29.00 3.9 (4.2) 3.5 (5.4) 6.4 6.3 6.7 6.1 13.7 (9.6) 12.7 (13.8) 8.5 

i-MeC29 29.33 8.4 (5.5) 7.7 (2.6) 8.0 6.8 7.9 6.5 25.9 (4.0) 25.4 (11.0) 7.1 

diMeC29 29.63 0.9 (0.7) 0.9 (0.4) 2.5 2.5 3.0 1.9 10.7 (0.9) 10.0 (2.5) 2.0 

30MeC29 29.74 1.7 (0.6) 1.6 (0.5) 0.6 0.1 0.4 0.3 5.1 (2.0) 4.1 )3.1) 1.5 

2-MeC30 30.64 8.2 (11.6) 9.1 (11.0) 2.1 2.0 1.8 1.9 2.4 (0.7) 3.1 (1.4) 0.3 

i-MeC31 31.31 12.3 (7.8) 11.8 (4.0) 3.5 3.7 3.6 3.7 2.6 (1.1) 3.6 (4.5) 1.3 

diMeC31 31.57 5.6 (2.5) 5.6 (1.6) 1.1 1.3 2.3 2.0 2.0 (0.0) 2.9 (2.1) 0.3 

i-MeC33 33.31 7.0 (7.5) 7.2 (7.0) 1.0 1.1 0.8 1.1 0.2 (2.4) 1.4 (5.2) 0.6 

diMeC33 33.57 10.5 (4.4) 10.8 (3.0) 0.7 0.7 0.3 0.7 0.3 (0.0) 1.2 (4.0) 0.0 

i-MeC35 35.31 1.3 (5.4) 1.4 (9.4) 0.3 0.2 0.2 0.3 0.0 (0.9) 0.5 (3.3) 0.3 

diMeC35 35.57 4.0 (3.5) 4.6 (4.3) 0.0 0.1 0.0 0.1 0.0 (0.0) 0.7 (4.5) 0.2 

i-MeC37 37.30 0.1 (2.1) 0.2 (5.1) 0.2 0.1 0.0 0.1 0.0 (0.0) 0.0 (0.0) 0.0 

diMeC37 37.54 1.1 (5.2) 1.6 (9.4) 0.1 (0.1) 0.0 0.0 0.0 0.0 0.0 (0.0) 0.0 

50 

Values are percentages for newly-emerged or young flies, except for those in parentheses which are for 5 day olds. 

1 Provisional identification; I-MeC25 represents internal-methylpentacosane. 2 Equivalent chain length. 3 From Promonis (1989), percentages are of alkanes only.

Cochliomyia macellaria 


Young females of C. macellaria generally have cuticular hydrocarbons of shorter chain length 

than Co. hominivorax with alkanes of chain length 27 (particularly i-methylheptacosane) being 

dominant. Also present are substantial quantities of n-nonacosane and i-methylnonacosane. 

Data for males and for older flies are not available. 

Distinguishing features for C. bezziana cuticular 

hydrocarbons (Fig. 32) 

Because of changes in cuticular hydrocarbon composition due to age, sex and probably 

geographic source, for reliable species identification it is best to consider the cuticular 

hydrocarbon pattern as a whole rather than to rely on one or two components. Thus cuticular 

hydrocarbon values for a supposed C. bezziana should match reasonably well with the 

values given in the Table and the traces in Fig. 32 for most if not all major components. 

However, allowance for changes in cuticluar hydrocarbon composition with age should be 

made using the values and the table as a yardstick. Since these values represent the limits 

for each component, flies of intermediate age should have intermediate hydrocarbon values. 

Culicular hydrocarbon changes cease with death so storage of a dead fly will not produce 

any further change in hydrocarbon composition. 

In spite of the cautionary note above, the following comments can be made: young 

C. megacephala, C. saffranea and Co. macellaria generally have shorter chain length 

hydrocarbons than does C. bezziana. Heptacosanes, especially i-methylheptacosane, are far 

more abundant than in C. bezziana, whereas hydrocarbons of chain length greater than 30 

are much more abundant in the latter. In view of the changes with age for the cuticular 

hydrocarbons of C. bezziana and Co. hominivorax, it is likely that similar changes occur with 

these other species, however, it is unlikely that these would be such as to cause older flies of 

these species to mimic C. bezziana. 

Newly emerged Co. hominivorax flies contain cuticular hydrocarbons dominated by 

nonacosanes which are only relatively minor components of C. bezziana and lack the longer 

chain material present in the latter. Older male Co. hominivorax flies develop large quantities 

of pentacosanes and heptacosanes which are absent or at low levels in C. bezziana. Older 

females of Co. hominivorax do develop some longer chain alkanes but not to the extent that 

C. bezziana does. They also have much more i-methylheptacosane and n-nonacosane but 

less 2-methyltriacontane than does C. bezziana. 

The single most diagnostic component of the cuticular hydrocarbons of C. bezziana is 

2-methyltriacontane, which is a major component in young and old males and females but is 

present at only low levels in the other species. Similarly i-methyltritriacontane is present in all 

stages of C. bezziana but occurs elsewhere only in old Co. hominivorax females. 

51


Figure 32: Gas chromatogram profiles of cuticular hydrocarbons of some Calliphoridae 

Arrows indicate n-nonacosane. 

52

8. Surveillance 

While SWF remains outside Australia’s borders, the early detection of an incursion provides 

the best hope for its subsequent control and eradication. Although the bulk of this manual is 

devoted to identification of myiases and the different life stages of SWF, the collection of SWF 

material for confirmation of its identity is of paramount importance. The three major activities 

in surveillance are: inspections of stock for myiasis and collection of larval samples, the trapping 

of adult flies and the collection of egg masses from sentinel animals. 

8.1 Specimen collecting from myiases 


In cases of suspected SWF myiases, samples of larvae must be taken from the host animal 

for identification. Up to 10 larvae should be pulled from the deeper parts of the myiasis with 

forceps and put in a sealed container for later processing, or dropped directly into 80 per cent 

ethanol. If facilities permit, live larvae can be killed in hot (below boiling) water which causes 

them to extend, before putting in formalin or 70-80 per cent ethanol. Alternatively, live larvae 

can be fixed by putting into Kahle’s I fixative for up to 24 hours, rinsing in water and storing in 

80 per cent ethanol. 

To rear out adults from mature larvae removed from host animals, the larvae should be put in 

a ventilated container with a small quantity of sand or vermiculite. The larvae will form puparia 

within a day and adults emerge approximately one week later, depending on ambient temperatures. 

Figure 33: A quarantine warning: Chrysoma bezziana infestation in foot and leg of dog. 

Note larvae evacuating wound via the cut pad. 

1. Kahle’s: 95% Ethanol (28 ml), 35% Formalin (11 ml), glacial acetic acid (4 ml), 

distilled water (57 ml). 

53


8.2 Trap (Fig. 34, Plate 8) 

Traps of numerous designs have been used for trapping flies in ecological studies and 

surveys. Evaluation of several trap designs by CSIRO in Papua New Guinea led to the 

development of a simple, cheap and efficient sticky trap, using the United States Department 

of Agriculture formulated bait, Swormlure (Spradbery 1981 and unpublished data). 

The trap is shown in Fig. 34. The roof is 24 gauge galvanised steel (80 x 60cm). The 

wooden base is 50 x 30 x 1cm marine-grade plywood 1 with a 2cm diameter hole in the 

centre. The base is suspended from the roof by two cradles of 4mm diameter fencing wire 

which are attached to the base with staples. The base and cradle are attached to the roof by 

pushing the 2.5cm angled ends of the wire through 1cm holes near the corners of the roof. 

The distance between roof and base (i.e. length of cradle arms) is 20cm. An aluminium plate 

(30 x 50cm), covered with insect trapping adhesive on one side, is attached (adhesive 

uppermost) to the plywood base with a binder clip. The plate has the long edges bent 

vertically to form a 3cm high flange which allow plates to be packed together in pairs without 

the adhesive (and trapped insects) coming in contact. 

The insect trapping adhesive 2 is put onto the plate with a broad-knife scraper and finished 

with a notched scraper (‘adhesive spreader’) to a depth of approximately 2-3mm. A 

manufactured ready to use sticky pad can also be used instead of the plate 3. 

The swormlure is dispensed from a 170ml polythene bottle which is screwed into a threaded 

plastic cap (3.8cm OD) attached by two screws to the under surface of the plywood base. 

The wick for release of the swormlure is either a cotton wool wick or four 12cm long fibre 

wicks (6.6mm diameter) in a 0.25mm thick propylene skin (as used for ink reservoirs in felt 

pens, etc.). Use of a cotton wool wick will result in more rapid evaporation of the swormlure 

and the propylene wicks are recommended for long term use. 

The composition of the swormlure is: 

Chemical Volume % (CSIRO) 

acetone 8.0 

sec-butyl alcohol 12.5 

iso-butyl alcohol 9.0 

dimethyl disulphide 14.3 

acetic acid 12.5 

n-butyric acid 17.0 

n-valeric acid 12.5 

phenol 3.6 

p-cresol 3.6 

benzoic acid 3.5 

indole 3.5 

1. Due to fires damaging the plywood base, a galvanised steel base is used in the Northern Territory (T.L. Fenner, 

personal communication). 

2. Suitable adhesives include: Tangle Trap (Tanglefoot Co., 314 Straight Avenue, Grand Rapids, Michigan 49504, USA: 

Fax (0011) 1 616 4594140, product no. 95400-25lb) and Tac-gel (Rentokil P/L, 554 Pacific Highway, Chatswood, 

NSW 2067: Fax (02) 412 4792, product code 200503-2 kg). 

3. Sticky trapping pads available from Starkeys Products, 46 Achievement Way, Wangara, WA 6065 

54

Screw-worm fly sticky trap design and assembly 

Figure 34: Screw-worm fly trap. 

55 


sticky pad 

The trap is supplied either complete or as a kit ready for assembly.


Measure solids first and add liquids, adding dimethyl disulphide last. It is crucial that the 

correct chemicals be used, especially the n-isomers of butyric and valeric acids. Care must 

be taken when mixing and dispensing swormlure which is very caustic, and has a long-lasting 

and unpleasant odour. Store in a refrigerator not used for foodstuffs. 

The traps are suspended by cords from trees or posts at a height of about 1.5m. For 

surveillance, maximising the opportunity for catching SWF is important and shady sites at 

the edge of wooded areas, near water sources or cattle camps are recommended. Close 

proximity to rubbish dumps or animal carcasses will result in large numbers of secondary 

blowflies on the traps and these sites should be avoided. 

Traps can be serviced at convenient intervals from daily to weekly. Up to 10 days exposure 

can be used but trapped flies deteriorate with time. In some locations, foraging stingless 

bees may remove the adhesive. When serviced, the aluminium plate is replaced and the 

swormlure container replenished. When large numbers of traps are being serviced, trap 

plates can be stored in plywood boxes (35 x 60cm in cross section) of sufficient length to 

hold the number of (paired) plates required. 

Flies on the trap plate are removed with forceps and placed on appropriately labelled (locality, 

trap number, date, etc.) cards or plastic petri dishes, using the residual adhesive to attach fly 

to card or dish. Cards or dishes can be stored in a freezer to await microscopical examination 

and identification. 

Larva of the New World screw-worm fly Cochlimyia hominivorax. 

Scanning electron microscope photograph by Colin Beaton 

56

8.3 Sentinels (Fig. 35, Plate 8) 


A wounded sentinel steer will attract about 4-5 times more SWF than a swormlure trap. 

Sentinel animals such as cattle and sheep are used primarily to attract gravid females 

which lay egg masses on the edge of the wound. The egg mass and/or resulting larvae are 

collected for diagnosis. During eradication programs employing sterile insect release, sterile 

and fertile egg masses indicate the relative success of the releases and sentinels are crucial 

for such monitoring. 

A three-panel pen which can be used as a crush for cattle has been used extensively by 

CSIRO for egg mass collections from sentinels throughout Papua New Guinea. Each panel 

(1.5 x 2.7m) is made form 20mm OD galvanised steel pipe with rails and support struts at 

25cm intervals. One or two panels are secured to a tree or steel post and the third panel 

attached to form a triangle. All attachments are by 12 gauge fencing wire. The animal is 

provided with water and a feed box containing lucerne chaff or hay. Fresh grass can also 

be provided if available. 

To restrain the sentinel, one panel is opened out a little to enable the second panel to be 

pushed inwards, with the animal facing the point of anchorage. 

Where smaller animals such as sheep and goats are available for use as sentinels, 

transportable sheep pens, as developed by the Mexican-American Commission for the 

Eradication of Screw-worms, can be deployed (Fig. 35). 

Pens should be sited where SWF activity is most likely such as the edge of forested areas, 

near sources of water, cattle and sheep camps or, in more open country, by using salt blocks 

and molasses to attract livestock in the area. 

To attract SWF and stimulate oviposition by gravid females, a wound with some 

sero-sanguinous exudate is necessary. With a scalpel blade, a 30-50mm incision is made 

through the dermis and into the underlying gluteal muscle of the rump. The upper rump 

gives easy access for observation and removal of egg masses. Egg masses are laid around 

the dry edges of the wound. Egg mass removal and servicing of sentinel pens is done daily, 

preferably during late evening or dusk when SWF activity decreases. The sentinel is held still 

(using the crush action of the cattle pen) and egg masses peeled off the host with scalpel 

and forceps. Egg masses in labelled pill boxes are stored in a freezer unless required for sterility 

check or rearing purposes. 

57


Figure 35: Sentinel pens for monitoring screw-worm fly activity. 

58

9. Acknowledgements 


I would like to thank Dr K.R. Norris for his comments and advice throughout the preparation 

of this manual. I also thank the following: Ms H. Geier and C. Beaton (scanning electron 

microscopy), A. Carter, C. Hunt and Ms S. Smith (line illustrations), J.P. Green (photography), 

Ms J. Hull (typing), Dr G.G. Foster, Dr N. Monzu, Dr D.P.A. Sands and Dr H.A. Standfast 

(additional colour transparencies), Dr W.V. Brown (cuticular lipid section), and G. Brown 

(preparation of additional bromides). For sending specimens I wish to thank O. Fahey, J. 

Feehan, A.C.M. van Gerwen, C. Tann, R.S. Tozer and G. Weller (CSIRO), Professor B. 

Greenberg (University of Illinois), Dr M.J. Hall (Natural History Museum, London) and Dr D.B. 

Thomas (The Mexican-American Commission for the Eradication of Screw-worms, Mexico). 

Larva of the Old screw-worm fly Chrysomya bezziana. 

Scanning electron microscope photograph by Helen Geier 

59


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Anon. (1989). A national screw worm fly preparedness review. Rpt. Foreign Diseases 

Unit, D.P.I.E., Canberra. 

Anon. (1990). A national review of Australia’s longer term screw worm fly (SWF) 

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Basset, C.R. and Sulaiman Bin A. Kadir, (1982). The screw-worm fly (Chrysomya 

bezziana) - an obstacle to large-scale beef production in Malaysia. Anim. Prod. 

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Erzinçlioglu, Y.Z. (1987). The larvae of some blowflies of medical and veterinary 

importance. Med. Vet. Entomol. 1, 121-125. 

Erzinçlioglu, Y.Z. (1989). The value of chorionic structure and size in the diagnosis of 

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Fuller, M.E. (1932). The larvae of the Australian sheep blowflies. Proc. Linn. Soc. NSW 

57, 77-91. 

Gabaj, M.M., Wyatt, N.P., Pont, A.C., Beesley, W.N., Awan, M.A.Q., Gusbi, A.M. and 

Benhaj, K.M. (1989). The screwworm fly in Libya: a threat to the livestock industry 

of the Old World. Vet. Rec. 125, 347-349. 

Graham, O.H. (Ed.) (1985). Symposium on eradication of the screwworm from the 

United States and Mexico. Misc. Publ. Entomol. Soc. Amer. 62, 68pp. 

Hightower, B.G., Adams, A.L., and Alley, D.A. (1965). Dispersal of released irradiated 

laboratory-reared screw-worm flies. J.Econ. Entomol. 58, 373-374. 

Humphrey, J.D., Spradbery, J.P., and Tozer, R.S. (1980). Chrysomya bezziana; 

pathology of Old World screw-worm fly infestations in cattle. Exp. Parasitol. 

49, 381-397. 

James, M.T. (1947). The flies that cause myiasis in man. U.S.D.A. Misc. Pub. 

No. 631, 175 pp. 

James, M.T. (1971). Genus Chrysomya in New Guinea. Pacific Insects 13, 369 

Kitching, R.L. (1976). The immature stages of the Old World Screw-worm fly, Chrysomya 

bezziana Villeneuve, with comparative notes on other Australasian species of 

Chrysomya (Diptera, Calliphoridae). Bull. Entomol. Res. 66, 195-203. 

Kloft, W.J., Noll, G.F., and Kloft, E.S. (1981). Introduction of Chrysomya bezziana 

Villeneuve (Diptera, Calliphoridae) into new geographic regions by transit 

infestation. Mitt. Deut. Ges. Allg. Ang. Entomol. 3, 151-154. 

Krafsur, E.S., Whitten, C.J. and Novy, J.E. (1987). Screwworm eradication in North and 

Central America. Parasitol. Today 3, 131-137. 

Liu, D. and Greenberg, B. (1989). Immature stages of some flies of forensic importance. 

Ann. Entomol. Soc. Am. 82, 80-93 

60

Lockey, K.H (1988). Lipids of the insect cuticle: origin, composition and function. 

Comp. Biochem. Physiol. 89B, 595-645. 

61 


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Rajapaksa, N. and Spradbery, J.P. (1989). Occurance of the Old World screw-worm fly 

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Spradbery, J.P. (1979). Daily oviposition activity and its adaptive significance in the 

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Spradbery, J.P. (1981). A new trap design for screw-worm fly studies. J. Aust. Entomol. Soc. 20, 

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Ann. Conf. Assoc. Vet. Insp. NSW pp. 56-62. 

Spradbery, J.P. and Owen, I.L. (1990). Efficacy of closantel against infestations of 

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Exp. Appl. 25, 75-85. 

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Spradbery, J.P. and Vanniasingham, J. (1980). Incidence of the screw-worm fly, 

Chrysomya bezziana, at the Zoo Negara, Malaysia. Malays. Vet. J. 7, 28-32. 

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the control of screw-worm fly, Chrysomya bezziana, in Papua New Guinea. 

Aust. Vet.J. 52, 280-284. 

Spradbery, J.P., Sands, D.P.A. and Bakker, P. (1982). Diel pattern of adult emergence in 

the screw-worm fly, Chrysomya bezziana (Diptera:Calliphoridae). J.Aust. Entomol. 

Soc. 21,301-302. 

Spradbery, J.P., Tozer, R.S. and Pound, A.A. (1983a). Efficacy of some acaricades 

against screw-worm fly larvae. Aust. Vet. J. 60,57-58.


Spradbery, J.P., Ford, R. and Tozer, R.S. (1983b). Diel larval exodus in the screw-worm 

fly, Chrysomya bezziana (Villeneuve). J Aust. Entomol. Soc. 22, 261-262. 

Spradbery, J.P., Pound, A.A., Robb, J.R, and Tozer, R.S. (1983c). Sterilization of screw- 

worm fly, Chrysomya bezziana Villeneuve (Diptera:Calliphoridae), by gamma 

radiation. J. Aust. Entomol. Soc. 22, 319-24. 

Spradbery, J.P., Tozer, R.S., Drewett, N. and Lindsay, M.J. (1985). The efficacy of 

ivermectin against screw-worm fly Chrysomya bezziana in vitro and in cattle. 

Aust. Vet. J. 62 , 311-314. 

Spradbery, J.P. Tozer, R.S., Robb, J.M. and Cassells, P. (1989). The screw-worm fly Chrysomya 

bezziana Villeneuve (Diptera: Calliphoridae) in a sterile insect release trial in Papua New 

Guinea. Res. Popul. Ecol. 31, 353-366. 

Spradbery, J.P., Vogt, W.G., Sands, D.P.A. and Drewett, N. (1991a). Ovarian development rates in 

the Old World screw-worm fly, Chrysomya bezziana. Entomol. Exp. Appl. 58, 261-265. 

Spradbery, J.P., Tozer, R.S. and Pound, A.A. (1991b). The efficacy of several insecticides against 

the screw-worm fly (Chrysomya bezziana). Aust. Vet. J. 68, 338-342. 

Sutherst, R.W., Spradbery, J.P. and Maywald, G.F (1989). The potential geographical 

distribution of the Old World screw-worm fly Chrysomya bezziana. Med. Vet. Entomol. 

3. 273-280 

Zumpt, F. (1965). Myiasis in Man and Animals in the Old World. Butterworths, London. 

xv, + 267 pp. 

Additional References and Further Reading 

Brown, W.V., Morton, R., Lacey, M.J., Spradbery, J.P. and Mahon, R.J. (1998) 

Identification of the geographical source of adults of the Old World screw-worm fly, 

Chrysomya bezziana Villeneuve (Diptera: Calliphoridae), by multivariate analysis of 

cuticular hydrocarbons. Comparative Biochemical Physiology 119B, 391-399 

FAO (1992) The New World Screwworm Eradication Programme, Food and Agriculture 

Organisation of the United Nations, Rome 192pp. 

Mahon, R.J. (2001). A trial of the sterile insect release method against the Old World screw-worm 

fly in Malaysia. Proceedings AOAD Conference on Control of Old World screw-worm fly, 

Bahrain 2001. 

Spradbery, J.P (1994). Screw-worm fly: A Tale of Two Species. Agricultural Zoological 

Reviews 6,1-61 

Spradbery, J.P (2001). A sterile insect release trial in Papua New Guinea. Proceedings 

AOAD Conference on Control of Old World Screw-worm Fly, Bahrain 2001. 

Spradbery, J.P., Mahon, R.J., Morton, R. and Tozer, R.S. (1994). Dispersal in the 

Old World screw-worm fly, Chrysomya bezziana. Med. Vet. Entomol. 8, 161-168. 

Spradbery, J.P., Khanfar K.A. and Harpham, D. (1992). Myiasis in the Sultanate of Oman. 

Veterinary Record. 127,76-77 

Spradbery J.P., Bromley, J., Dixon, R. and Tetlow L. (1994). Tungiasis in Australia: an exotic 

disease threat. The Medical Journal of Australia. 161, 173. 

62

Plate One. 

LIFE CyCLE OF SCREW-WORM FLy 


Plate page 


Oviposition Egg Masses 

Larval Infestation Mature Larvae 

Larval exodus Puparia

Plate Two. 

Plate page 


COuRSE OF SCREW-WORM MyIASIS 

Chrysomya bezziana on steer (small infestation). 

Day 1 Day 2 

Day 3 Day 4 

Day 5 Day 6

Plate Three. 

Plate page 


COuRSE OF SCREW-WORM MyIASIS 

Chrysomya bezziana on steer (large infestation). 

Day 1 Day 2 

Day 3 Day 4 

Day 5 Day 6

Plate Four. 

Plate page 


RESOLuTION OF MyIASES 

Chrysomya bezziana on steers 

Day 1 Day 2 

WOuND BIOPSy 

Infestation of steer with Chrysomya bezziana 

Cross section of early 3rd - instar larva of C. bezziana 

surrounded by a zone of necrosis and haemorrhage.

Plate Five. 

Plate page 


EXAMPLES OF SCREW-WORM MyIASIS 


Post-castration myiasis Myiasis in navel of brahman calf 

Myiasis in vulva of ewe Myiasis in rectum of ram 

Shoulder myiasis in dog Cat with myiasis in shoulder

Plate Six. 

Plate page 


SECONDARy FLy SPECIES 

Egg masses of Chrysomya saffranea Larvae of Chrysomya megacephala 

SHEEP BLOWFLy (Lucilia cuprina) 

Initiating a myiasis Sheep blowfly myiasis

Plate Seven. 

ADuLT FLIES 

Plate page 


Chrysomya bezziana (PNG). Cochliomya hominivorax (Mexico). Calliphora stygia (Australia). 

Chrysomya bezziana (Africa). Chrysomya megacephala (PNG). Wohlfahrtia nuba (Oman). 

Top, C. bezziana (PNG). Top, C. saffranea (PNG). Top, C. bezziana (PNG). 

Bottom, C. bezziana (Africa). Middle, C. megacephala (PNG). Middle, C. saffranea (PNG). 

Bottom, C. rufifacies Bottom, C. rufifacies

Plate Eight. 

Plate Page 


MONITORING SCREW-WORM FLy ACTIVITy 

Fly Trap 

Sentinel Pen

Manual for Diagnosis of Screw-worm Fly - xcs consulting

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