New World screwworm cases increase and may go undetected in wildlife; specialists look to hunters for early detection

More than 100 cases of New World screwworm have been logged in 2026, with many of those cases being found in cattle. It is the first time in more than 50 years that the flesh-eating fly is spreading on U.S. mainland, and it not only puts cattle at risk but all warm-blooded animals. 

Jacob Dykes and Eric Michel, co-directors of Mississippi State University’s deer lab, report for The Conversation that susceptible animals include commonly hunted ones: deer, elk and waterfowl. Dykes and Michel write that hunters can serve as an early warning system. "Wildlife agencies are already asking them to be vigilant and report any signs of screwworm infestations."

The issue with the New World screwworm is they feed on living flesh, as opposed to dead tissue. They plant larvae in open wounds, or in the eyes or noses of deer and elk. Tick bites, small scratches, umbilical stumps or skin-shedding antlers can attract the parasite. Once eggs hatch, they burrow into the animal’s flesh, inviting more infection until death.

The Americas saw a widespread problem with the infection in cattle in the 1950s, but screwworm was largely eradicated by 1966 with treatment efforts and by releasing millions of sterilized male flies to reduce the population. "Sterile flies kept the parasite south of Panama for years, but the movement of cattle and wildlife likely brought it north again. Since 2022, the parasites have been reproducing and moving farther northward."

Screwworm came back to the U.S. in June 2026 in a calf in Texas. As of Nov. 5, detections have reached 116. The U.S. government is ramping up its use of sterile flies. However, wildlife are much more likely to carry screwworm undetected, which makes it more difficult to plan which areas to release flies. Specialists like Dykes and Michel are looking toward hunters to report symptoms to their state’s wildlife agency, the U.S. Department of Agriculture or to local veterinarians.