The United States has confirmed 50 New World screwworm detections since the first one turned up in a Zavala County calf on June 3, 2026. Forty-eight are in Texas, two are in New Mexico, and as of September 21 only three are listed as active. The most recent is a horse in Grant County, New Mexico. Not one of those 50 is a free-ranging white-tailed deer — and that is the number Texas hunters should be watching, because the state's deer herd runs north of five million animals and archery season is already open.
Here is what screwworm actually is, what has changed on the ground, and the four things a hunter is being asked to do about it.
Why this parasite is different
Most fly larvae eat dead tissue. Cochliomyia hominivorax does not. Screwworm larvae feed on living flesh, which is the entire reason this insect gets a federal eradication program and a blowfly does not. A female lays a few hundred eggs at the edge of a wound — a fresh cut, a tick bite, a navel, a castration site, the raw pedicle where a buck just dropped an antler — and the larvae burrow inward, widening the wound and drawing more flies to it. An untreated animal can die in a week to two.
The US eradicated screwworm by 1966 and pushed the barrier down to the Darién Gap in Panama. Before that, it was one of the largest sources of wildlife mortality in South Texas. Texas Parks and Wildlife has put the pre-eradication figure at roughly 80 percent of newborn fawns killed in affected country. That is not a modeled projection. That is what the record says happened.
What is actually restricted right now
The Texas Animal Health Commission counts cases across 17 Texas counties and 39 premises, and maintains active NWS Infested Zones in 14 of them: Brewster, Crockett, Edwards, Jeff Davis, Jim Hogg, Pecos, Presidio, Schleicher, Starr, Sutton, Terrell, Uvalde, Val Verde and Zapata.
Inside a zone, any warm-blooded animal moving out has to be inspected by TAHC or a certified inspector and travel with a movement and treatment certificate. That sweeps in deer breeder facilities and any live animal transport, and it is the only binding restriction on the hunting side. Two zones — La Salle and Webb, and Gillespie, Kerr and Kimble — were released on August 31, so the county list moves in both directions.
No state has changed a hunting season, a bag limit, or a carcass-movement rule because of screwworm. If you read otherwise this fall, check the agency page before you rearrange a trip. The rules that did change are livestock movement rules and a set of FDA emergency authorizations issued August 31, one of which — a Zoetis doramectin injectable — is the first such listing to name deer, and is veterinarian-administered only.
The sterile-fly program, in numbers
The control strategy is the same one that worked sixty years ago: flood the landscape with sterilized males so that wild females, which mate once, mate with a dead end.
| Facility | Role | Capacity |
|---|---|---|
| Pacora, Panama | Production | ~100 million flies/week |
| Metapa, Mexico | Production (completed June 2026) | 100 million/week |
| Moore Air Base, Texas | Production plant under construction | 300 million/week projected |
| Moore Air Base, Texas | Dispersal (operational) | up to 100 million/week |
More than a billion sterile flies have been released over Texas since February 2026, with a stated goal of 500 million a week by summer 2027. Figures are USDA APHIS's, from its production and dispersal facility page. Whether that cadence holds the line is the open question, and nobody serious is claiming certainty about it.
What you are being asked to look for
USDA launched a wildlife-facing screwworm page with a hunter factsheet and a wallet card this month, and it is short enough to read at a feeder. The signs, per APHIS and TPWD:
- In a live deer: an open wound with live maggots in it. Head shaking, obvious irritation, isolation from the group. A foul, rotted-flesh smell you can catch downwind.
- In an animal you just killed: maggots present on a fresh carcass — not one that has laid out for a day — plus bloody discharge and that same odor.
- The fly itself: housefly-sized, metallic blue-green, three dark stripes down the back, and orange-red eyes. The eyes are the tell.
Where it lands on a deer is worth knowing: the navel on a fawn, the genitals, any injury, and the antler pedicle wound after a shed. Early season in Texas is warm and buggy, which is the same reason you are already layering light and covering skin in October.
What to do, in order
- Do not handle or move the animal. Photograph it, mark the GPS point, back off.
- Report it. In Texas, call your TPWD wildlife biologist at (512) 389-4505. Anywhere else, USDA Wildlife Services at 866-487-3297. Agencies have said repeatedly that early detection is the whole ballgame, and a hunter in a blind is a better detection network than any survey they can fund.
- Protect yourself while you work. Cover open cuts, use an EPA-registered repellent, and treat field clothes with 0.5 percent permethrin. Check yourself afterward the same way you check for ticks.
- Work clean. This is ordinary field-care discipline and it is worth more than it sounds like: gloves on, a knife sharp enough that you are not sawing and tearing, and a carcass cooled fast. A sharp blade makes clean cuts and fewer of them — we walked through field sharpening earlier this year, and the knife and field-care shelf is stocked around exactly that. A small, fixed-blade caping knife like the Mora Eldris is the one most people are missing.
The two questions everybody asks, answered honestly
Can I get it? There has been one confirmed US human case — August 2025, travel-associated, acquired in El Salvador. No locally acquired human infestation has been reported. CDC describes the risk to people as very low. Myiasis in humans is treatable and it starts with a wound that will not heal, so if you have one, see a doctor rather than a forum.
Is the venison safe? This is where I have to stop short of what you probably want. Neither APHIS nor TPWD has published guidance on eating meat from a screwworm-infested deer. Secondary sources say it is fine; I am not going to launder that into an agency position it does not hold. The defensible answer is the one that covers every disease: do not eat an animal that was visibly sick when you killed it, and if you find live maggots in a fresh carcass, report it and call your biologist before you process it.
What to watch between now and the general opener
Three things will move. The case count and the active-case number, which have changed twice in September alone. The Texas infested-zone county list, which gained and shed counties in the same month. And the answer to the one question the program has not had to face yet: whether a free-ranging Texas whitetail turns up positive once a few hundred thousand hunters start putting hands on deer in November.
That is not a prediction. It is an observation about detection effort. A parasite that has been confirmed 48 times in Texas livestock and horses has been searched for by ranchers and veterinarians. Deer season is about to add several million more sets of eyes, in the same country, at the same time. If you are heading out for the October 3 archery opener or planning around the general season zones, put the reporting number in your phone. It costs nothing, and it is the single most useful thing a hunter can do about this one.
We are tracking the same way we track CWD by state — as a page that gets updated, not a story that gets filed.