true screwworm
Quick Summary
Screwworms are a type of blow fly, named for the screw-like appearance of their larvae. The larvae of the true screwworm (Cochliomyia hominivorax) are serious pests that infest the wounds or mucous membranes of animals, including livestock, deer, and occasionally humans.12
Female screwworm flies lay eggs near open wounds. The larvae burrow into the tissue, feeding and growing. Severe infestations, known as myiasis, can be fatal to the host animal, sometimes within two weeks.12
The Sterile Insect Technique, developed in the mid-1900s, has been used to control screwworm populations by sterilizing male flies and releasing them to mate with fertile females, thereby preventing reproduction. This method has been successful in eradicating screwworms from large areas, though outbreaks can still occur. In June 2026, the U.S. Department of Agriculture confirmed the presence of screwworm larvae in Texas, marking the first outbreak in domestic animals since the 1970s.21
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