Field Guide to Venomous and Medically Important Invertebrates ...

Larvae are obligate parasites in the nostrils and frontal sinuses of sheep, goats, camels and
horses, while people are usually are only incidental hosts. However, ocular infestation of
humans by O. ovis is not uncommon, and several cases occurred among U.S. military personnel
during the Persian Gulf War. Female flies are larviparous, and they deposit larvae directly into
the human eye while in flight. Normally, infestations produce a painful form of conjunctivitis
that usually self-resolves. However, larvae are capable of penetrating the inner eye, causing
serious complications.
Sheep Maggot
The genus Chrysomya is confined to the Old World where it is restricted to tropical and semi-
tropical regions. One species, C. chloropyga, is an important sheep maggot in South Africa,
although there are numerous examples of this species infesting wild and domestic animals, and
people. Female flies lay eggs singly or in batches inside wounds, sometimes on the unbroken
skin covering bruises and abscesses, and occasionally on places soiled by blood from wounds.
Young larvae feed on liquids exuding from the interior of the wound for about a day; and later
they embed in the living tissue. The larvae become full fed in about 6 days, exit the wound and
drop to the ground where they bury themselves beneath the surface of the soil. Pupation takes
place in 1-2 days and typically lasts 7-9 days. The biotic potential of the fly is enormous as a
single female may produce 500-600 eggs and there may be 8 or more generations per year.
Figure 170. Adult Chrysomya sp. Photo: Anabel Martinez.
Figure 171. Adult Chrysomya sp. Photo: Marcelo de Campos Pereira.
Screw Worm Flies