Flesh-Eating Fly Returns: Parasite Threatens US Southwest

Screwworm, a parasitic fly known for its flesh-eating larvae, has reappeared in the U.S. Southwest this June, marking its first presence in the region since the 1970s. This resurgence presents a serious risk to the livestock industry, as well as to wildlife and household pets. Female screwworm flies lay eggs in wounds, and their hatched larvae consume living flesh, which can be fatal if left untreated.

Pet owners should monitor their animals for symptoms such as swollen or non-healing wounds, pus discharge, excessive licking, lethargy, or appetite loss. A foul odor resembling rotting flesh is a key indicator. While screwworm primarily affects animals, experts note it rarely harms humans and poses no food safety risks. Prompt veterinary care, including maggot removal, wound cleaning, and antibiotics, generally leads to full recovery.

Preventative measures include monthly medications typically used for fleas and ticks, as some treatments can protect against screwworm. Veterinarians emphasize that self-treatment is not advised, as missed larvae can continue to burrow and spread. Local and federal agencies, including the U.S. Department of Agriculture, are increasing surveillance and producing sterile flies to control reproduction, though current production levels are insufficient to fully suppress the outbreak.