The resurgence of the New World screwworm fly (Cochilomyia hominivorax) isn’t just a danger to cattle—it’s also harming and even killing people. Researchers in Mexico analyzed data on local cases of screwworm reported over the past few years. Since 2025, they found, hundreds of residents have been infested by the parasitic fly’s maggot larvae and at least one person likely died as a result. The findings indicate that the screwworm’s return to Mexico and more recently the United States will be a public health threat to both livestock and people. “Coordination between human health, animal health, wildlife, and agricultural sectors will be essential to guide prevention and control measures,” the authors wrote in their paper, published last week in the journal of Emerging Infectious Diseases. A deadly return Unlike many fly species, screwworm maggots prefer to feed on the living flesh of warm-blooded animals. The flies lay eggs on a host via open wounds or mucous membranes, and then the maggots use their screw-like bodies and sharp mouth hooks to burrow themselves deeper into the animal. This burrowing can cause extensive, even life-threatening tissue damage, as well as raise the risk of serious secondary infections.