The Screwworm Fly is Back!
I just read an article from the National Deer Association and I'll be honest — it stopped me cold. This thing is freaky, it's disgusting, and it's heading straight for Texas deer country.
The screwworm fly is 160 miles from the Texas border. Fawning season is happening right now. If you manage land, run trail cameras, or plan to hunt deer this fall, you need to understand what this is and what to do about it.
What Is the Screwworm Fly?
The New World screwworm fly looks like an ordinary fly. Its life cycle is anything but.
Normal maggots eat dead tissue. These don't. The larvae of the screwworm fly burrow into living flesh and eat from the inside out. They target open wounds, mucous membranes, and body openings of their victims — deer, livestock, dogs, other small mammals, and in rare cases, people.
For deer, there are two especially dangerous windows. Right now — spring and early summer — newborn fawns are vulnerable through their umbilical cords. In fall, bucks carry fresh wounds from fighting that become prime targets. Both windows are wide open.
Once a wound is infected, it attracts more flies. More flies lay more eggs. The wound grows. Without direct human intervention, the animal dies. In a 2016 outbreak on Big Pine Key in Florida, screwworms killed nearly 20 percent of the entire endangered Key deer population. Biologists found living deer with maggot-filled craters on their heads, necks, mouths, and hooves. Go read the full NDA article — the photos are something else.
We Beat This Before — Then Lost It
Senior hunters in Texas remember the screwworm from the 1950s when it devastated deer and livestock across the Southeast. The USDA came up with one of the most creative eradication strategies ever used in wildlife conservation — they sterilized male screwworm flies using radiation and released them by the millions. Female flies mated with sterile males, laid non-viable eggs, and populations crashed.
By 1966, the screwworm fly was eradicated from the United States. By 2001, it had been pushed all the way down to South America.
We thought we won. We almost did.
How It Came Back
The COVID pandemic disrupted sterile fly production at the key facility in Panama. The fly took advantage. In August 2022, it broke through the Darien Gap — the jungle barrier between Panama and Colombia — and started moving north.
The Darien Gap used to be impenetrable forest with no roads and no livestock. In recent years, large sections have been cleared for cattle grazing. With livestock came food. With roads came access. The natural barrier was gone, and the fly moved through.
By November 2024, it reached Mexico. By summer 2025, the USDA and Mexican government tried to stop it at the Isthmus of Tehuantepec — a natural bottleneck 600 miles from the Texas border. They didn't stop it.
As of April 8th, 2026, active screwworm cases have been confirmed in cattle, pigs, horses, and dogs in northeast Mexico. The closest confirmed case is 160 miles from the Texas border in the state of Tamaulipas.
Blaise Korzekwa, White-tailed Deer Program Leader for TPWD, said it plainly: "With the current fly production, unless something changes, it looks like it's likely going to make its way into Texas at some point."
The USDA is currently releasing 100 million sterile flies per week in Mexico and dropping them 50 miles into South Texas as a precaution. It's working in those specific areas. The problem is scale — eradicating the fly in the 1960s required more than 500 million sterile flies per week. A new facility in Mexico is under construction and could be ready this summer. A third facility at Moore Air Base in Texas has been announced but is two years from completion.
The race is to scale up production before the fly crosses the border.
What You Can Do Right Now
Keep your trail cameras running. Spring and summer, when most cameras come down after hunting season, is exactly when you need eyes on deer. Look for animals showing signs of distress or visible wound activity. Maggots actively moving in a wound — that is your signal.
Report anything suspicious immediately. If you see a deer, dog, rabbit, wild turkey, or any animal with live maggots in a wound or body opening, contact TPWD and your local biologist right away. Early detection is the difference between a contained outbreak and an established population.
Talk to your veterinarian if you run livestock. Cattle, horses, goats, and pigs are actually the primary sentinel species for this fly. Cases in livestock will likely show up before deer populations do. Know what to look for before it shows up on your place.
Register for the April 22nd webinar. The USDA and Department of the Interior are hosting a joint webinar specifically for the wildlife and hunting community on screwworm preparedness and response. If you manage land or run a hunting operation in Texas, that webinar is worth your time. Registration link is in the show notes of the podcast episode.
The Bottom Line
This is a real threat moving in real time toward Texas deer country. The agencies are working the problem — TPWD, USDA, the Mexican Department of Agriculture — but the outcome is not guaranteed. Production capacity is still short. The fly is still moving. And fawning season is right now.
Stay informed. Keep cameras up. Report anything suspicious. Share this with every hunter and landowner you know in Texas.
