Field Guide to Venomous and Medically Important Invertebrates ...

Chrysomya bezziana (Calliphoridae), Old World screwworm fly, is the most important myiasis-
producing fly in tropical areas of Africa, Asia, India, some Indo-pacific islands, and the Middle
East. Cattle and other ungulates are the primary hosts. This species ranks second only to the
tsetse flies as a pest of cattle in central and southern Africa, and is of considerable importance as
a pest of people in India. For unknown reasons, people are attacked with relatively more
frequency in India than in other parts of the fly’s range. Larvae attack wounds on various parts
of the body, but infestation of the eyes, nasal cavities, and head wounds are the most frequent
locations. This species does not breed in carrion or excrement, and it is dependent upon living
tissue for its existence.
Cochliomyia hominivorax historically was distributed from the southern U.S. southward
throughout most of Latin America and the Caribbean. However, this pest is now eradicated as
far south as Panama, and many areas of the Caribbean. These flies historically produced
devastating economic losses throughout their range by damaging and killing livestock. Military
personnel with battlefield wounds or other injuries also can be susceptible to invasion by
screwworms. Several soldiers wounded in Operation Just Cause, returned to the U.S. from
Panama with active screwworm infestations. Adult screwworm flies find superficial wounds on
warmblooded animals and feed on fluids in the wound. Early stages of the larvae feeding in a
wound are very difficult to see and only slight movements are normally observed. As the larvae
feed, the wound is gradually enlarged, becoming wider and deeper. By the third day of
infestation, as many as 100 to 200 tightly packed, vertically oriented larvae can be observed
embedded deep in the wound. Screwworm larvae tend to burrow deeper in a wound when
disturbed and generally they do not crawl on the surface. A discharge often exudes from the