Vol 10 Part 14. An introduction to the immature stages of British Flies ...

Forensic or medico-legal importance
After death animal and human corpses are invaded by a succession of insects and
other invertebrates associated with the various stages of decomposition. Not surprisingly,
many of the Diptera involved are of the same families, and frequently the same
species, as those involved in myiasis. The most important decomposers are blowfly
(Calliphoridae) larvae of the genera Calliphora and Lucilia.
Identification of the species involved, combined with a knowledge of their rates of
development and ecology, enables an estimate of time of death to be made. It may also
be possible to establish if a body has been moved or concealed for part of the time. The
faunal succession on carrion is dealt with in the section on life-histories and ecology and
the forensic aspects are fully covered elsewhere (Smith, 1986b ).
Another important medico-legal involvement with larvae is their presence on foodstuffs,
drugs, etc. in domestic or commercial premises. Frequently entomologists are
asked, usually by environmental health officers, not only to identify such larvae but to
give additional information on the age of the larva, its country of origin and whether it
could have survived refrigeration. This enables the possible source and time of infestation
to be estimated and blame to be apportioned in cases involving prosecution.
Bus vine ( 1980) is particularly valuable for this type of enquiry and Oldroyd (in Smith,
1973) is useful. Such enquiries may involve larvae of non-British species and the larvae
of the commonest of these are included in the present Handbook, e.g. Ceratitis capitata
(Wiedemann) (Mediterranean fruit fly, in oranges, lemons, mangos, etc.), Rhago/etis
cerasi (Linnaeus) (cherry fruit-fly in cherries and cherry yoghurt) (both Tephritidae);
Hermetia il/ucens (Linnaeus) (Stratiomyidae, in tinned tomatoes, black peppers, root
ginger, mango slices in brine, etc.) (Smith & Chainey, 1989).
Some common types of 'economic' enquiries involving native British species (plus
Hermetia illucens) are listed below with the fly larvae involved in order of frequency of
occurrence in cases I have dealt with over a period of more than 30 years.
A. Larvae in foods, drinks, etc.
I. Meat and meat products, poultry, fish, etc.: Calliphora, Lucilia, Hermetia illucens, Sarcophaga,
Hypoderma (in venison).
2. Cheese: Calliphora (also butter), Piophi/a, Fannia (sometimes in wrappings of other animal
protein foods, e.g. butter), Sarcophaga.
3. Eggs, broken and bad: Muscina (Muscidae), Megaselia (Phoridae).
4. Milk bottles (empty or full); Spiniphora bergenstammi (Mik) (Phoridae), Drosophila (especially
D. funebris (Fabricius) and D. busckii Coquillett) (Drosophilidae), Calliphora, Muscina.
Psychodidae (Psychoda surcoufi Tonnoir), Syrphidae (Syrphini, Eristalis), Trichocera
(Trichoceridae).
5. Vegetables & vegetable products: Phoridae, Sciaridae, Hermetia illucens, Syrphidae,
Lonchopteridae, Chironomidae (Metriocnemus in salads including watercress).
6. Fruit & fruit products: Eristalis, Tephritidae, Drosophilidae, Hermetia illucens, Muscina
stabu/ans (Fallen).
7. Alcoholic & fruit drinks, vinegar, etc.: Drosophilidae larvae may still be recognisable in dehydrated
food after reconstitution (see Sciaridae).
B. Larvae in domestic premises
I. Larvae emerging from soil, cracks in concrete, etc. (especially after heavy rain), in numbers on
concrete surfaces or indoors: Tipu/a, Lucilia.
2. Indoors (including upstairs rooms): Volucella (from wasps' nests in loft), puparia of Crataerina
pallida (from swift and house-martin nests), Calliphora (from nearby corpse (bird, mouse, etc.
in loft, chimney, under floorboards or carpets)), Scenopinus (in or under carpets), Syrphus
(from leaves of cut flowers, salads, etc.), Sciaridae in neglected houseplant pots (and Oldroyd
(1964) records a bizarre case where sciarid larvae infested the mouldy peaty material used as a
fire-resisting lining in an office safe).
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