Atlas of livestock parasites
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Chrysomyia bezziana



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Cattle screwworm

Also Callitroga hominivorax (synonym: Cochliomyia americana); Callitroga macellarla (synonym: Cochliomyia macellarla)

General Description:
Adult flies are 10 to 15 mm long with bluish-green bodies. The thorax has three longitudinal stripes, and the face and eyes are brown. Mature larvae are 10 to 15 mm long with bands of spines around body segments.

Life Cycle:
Female flies deposit eggs at the edges of wounds on the host. Larvae hatch in 10 to 12 hours and mature in 3 to 6 days before dropping from the host to pupate in the ground. Pupae become adults in 3 to 7 days.

Larvae inhabit skin around wounds of any size. Geographic

Callitroga hominivorax - Southern Mexico, Central America and South America, generally in warmer areas.
Callítroga macellaria - North and South America, from Canada to southern Argentina.
Chrysomyia bezziana - Africa, southern Asia.


Severe disease is common in screwworm fly areas. Death occurs frequently, causing serious economic losses.

Effect on the Host:
Screwworm myiasis begins in wounds as minor as tick bites. Larvae digest tissue as they migrate, expanding the lesion. Secondary bacterial infections are common and may cause death. Wounds have a putrid odor, and foul-smelling liquid oozes out. Affected animals often isolate themselves from the herd and seek protection in shade and bushes.

Diagnostic Information:
Identification of adult flies and larvae is the only diagnostic method.

Adult screwworm f1ies mate only once during their lives. In 1958, 20 billion sterilized male f1ies were released in the southern United States to compete in breeding with normal males. This program eliminated screwworm in the United States within 2 years. Other control measures are limited in effectiveness, and include treating wounds with insecticides.


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