For decades, the New World screwworm was something many Texans knew only from stories told by older ranchers and wildlife professionals. It was a flesh-eating parasite that once caused devastating losses to livestock and wildlife before being eradicated from the United States through one of the most successful insect control programs ever undertaken.
Now it’s back.
Since the first confirmed U.S. case was identified in a calf in Zavala County on June 3, New World screwworm has spread to multiple Texas counties, prompting an aggressive response from state and federal agencies. While much of the attention has focused on livestock, wildlife experts say hunters and landowners should also be paying close attention.
Or use the Dark Outdoors Linktree to find the program on your favorite platform.
Unlike the maggots most people are familiar with, New World screwworm larvae feed on living tissue. Female flies lay eggs in fresh wounds, and the larvae burrow deeper as they feed, causing extensive damage if left untreated. Cattle are among the most commonly affected animals, but virtually any warm-blooded animal—including deer, exotic game, sheep, goats, horses, dogs and even people in rare cases—can become infested.
That makes this much more than an agricultural issue.
Texas has invested decades restoring native wildlife, including desert bighorn sheep, while private landowners have spent millions improving habitat for white-tailed deer and other game species. A parasite capable of affecting virtually any wounded animal has the attention of wildlife managers for good reason.
Fortunately, there is encouraging news.
The same sterile fly program that eliminated New World screwworm from the United States decades ago remains the primary weapon against today’s outbreak. By releasing millions of sterile male flies into affected areas, scientists dramatically reduce reproduction because female screwworm flies mate only once. Combined with quarantines, movement restrictions, surveillance and rapid treatment of infected animals, officials hope to stop the parasite before it becomes established.
Another positive sign is that, as of this writing, confirmed Texas cases have involved domestic animals. Wildlife professionals are working aggressively to keep the parasite from becoming established in free-ranging wildlife populations.
Hunters can also play an important role. Summer trail camera surveys, time spent checking feeders or simply observing wildlife in the field can provide opportunities to notice animals with unusual wounds. Any suspicious infestations should be reported immediately to animal health officials rather than ignored.
The return of New World screwworm serves as a reminder that conservation victories are never permanent. Diseases and parasites don’t recognize fences or property lines, and protecting Texas wildlife often requires cooperation between ranchers, hunters, wildlife biologists and veterinarians.
The good news is that Texas has defeated this parasite before. The challenge now is making sure history repeats itself.
By the Numbers
New World Screwworm in the United States (USDA, July 5, 2026)
- 32 confirmed animal cases
- 30 domestic animal cases
- 1 confirmed wildlife case
- 18 active cases
- 12 inactive cases
- 2 states affected: Texas and New Mexico
- Texas counties with confirmed detections: Crockett, Edwards, Gillespie, Jim Hogg, La Salle, Pecos, Uvalde, Zavala, Medina and Terrell
- Species affected: Cattle, sheep, goats and dogs