Screwworm and Your Pets: A Texas Owner's Guide to Wounds, Flies, and Reporting

A yard dog in Crockett County was confirmed with New World screwworm on August 31 — the twelfth infestation in the county USDA calls this outbreak's epicenter, and the third Texas dog diagnosed since June. That detail matters more than the feedlot headlines if you keep animals at home, because the fly does not care whether the warm body in front of it belongs to a ranch horse or to the heeler on your porch.

The parasite has been back in Texas since June 3, when a three-week-old calf near La Pryor became the first confirmed U.S. case in roughly 60 years. By late September, USDA had logged 50 Texas infestations across 17 counties, in cattle, sheep, goats, horses and dogs. Every one of them started as an open wound that a fly found before it healed.

Our live Texas screwworm tracker carries the county-by-county map and the current quarantine picture. What follows is the part that applies to the dog in your truck and the cat on the back porch.

What makes a pet a target

The New World screwworm is not a filth fly. It does not want your garbage, and it is not looking for a carcass. A gravid female lays her eggs at the edge of living tissue — a fresh cut, a scraped knee, a hot spot a dog has licked raw, a torn dewclaw, a surgical incision that has not closed. The Texas A&M AgriLife Extension overview is the clearest short account of how the fly works. The larvae that hatch do not graze across the surface; they screw head-down into the wound and feed on flesh that is still attached and still bleeding, which is why an untreated infestation gets worse instead of crusting over.

Two consequences follow. Risk is highest for animals with a reason to have broken skin — working dogs, outdoor cats that fight, seniors with skin infections, pets fresh out of surgery. And timing matters: warm weather is what put this fly on the Texas landscape in the first place, and South Texas rarely gets cold enough to shut it down, so an untreated wound in Laredo in December deserves the same attention as one in July.

The check takes five minutes

You are not looking for a fly. You are looking for a wound that has stopped behaving like a wound. Work through your animals once a week while the weather is warm, and after any outing into brush or any scuffle that ends with a limp.

Start where the skin is thin and the hair is short: inside the ears, between the pads and up the back of the paws, the tail base, under the collar or harness line, and anywhere the animal has been licking. A screwworm wound is small at the start and unmistakably wrong within a day or two. It grows. The edges look undermined and matted rather than scabbed, and there is often a sweetish, rotting smell out of proportion to the size of the injury. The larvae appear to be sinking into the tissue rather than sitting on top of it. The animal may go off feed, pace, or hide.

A mangled, enlarging, foul-smelling wound is not a wait-and-see situation — and neither is a tick bite the dog has chewed into a crater, which is exactly the broken skin the fly is built to find. Staying ahead of fleas and ticks on Texas pets keeps a lot of that broken skin from existing in the first place.

If you find larvae, stop before you dig

The instinct is to pull them out with tweezers. Do not. Screwworm larvae anchor into living tissue, so crude removal tears the wound, leaves fragments behind and can drive the infestation deeper — and old ranch remedies like oil, kerosene or petroleum jelly smeared over broken skin are worse than useless. Call a veterinarian, keep the animal quiet, and let the phone calls happen in this order.

1. Vet first. Say plainly that you suspect screwworm so the clinic can prepare. Deep wound cleaning and any approved treatment product are a job for someone with the right tools; FDA emergency use authorizations issued during this outbreak cover topical options a veterinarian can apply.
2. Then report. The Texas Animal Health Commission takes suspected cases at 1-800-550-8242, and a suspicion is worth the call before any lab confirmation. Every case in this outbreak started with somebody noticing and picking up the phone.
3. Cover, don't seal. A loose gauze wrap protects the wound while you travel. Do not pack it airtight.
4. Limit movement. Livestock inside a TAHC infested zone are under movement restrictions, and several states tightened their rules on dogs and cats leaving affected Texas counties this summer — shelters felt the delays first. If you are traveling out of state with an animal, check the current zone map and your destination's requirements, and carry a recent veterinary certificate.

Cutting fly pressure around the house

You cannot inspect your way out of this alone, because the fly arrives from beyond your fence line. What you can do is make the property less interesting to flies and keep broken skin out of the equation.

Remove what actually breeds flies: uncovered garbage, dog waste left in the yard, wet compost, fallen fruit, and any dead animal on the property — including the armadillo under the deck. Repair screens. If a pet has an open wound, keep it indoors through the brightest part of the day, when flies are most active, and treat hot spots and lick granulomas promptly rather than letting a small skin problem become an open invitation.

If you are already fighting heavy fly, tick or flea pressure around a yard full of animals, it makes sense to bring in help. A licensed technician can knock the population back with targeted treatment rather than fogging the whole property; in South Texas the same quarterly visit takes in the mosquitoes and ants waiting on your return, which is how pest control in San Antonio and pest control in Laredo are typically structured. For what that service covers, see our pest control service overview.

Winter is an opening, not an all-clear

Cold is the response's best ally. Sustained freezes slow screwworm fly activity sharply and kill it outright across most of Texas, which is why the parasite never established itself north of the border during the decades it was endemic in Mexico, and why the sterile-fly campaign now has a window to work with. Texas went from 31 new cases in June to two in September, and the quarantine map has been shrinking since late August as zones are released.

None of that changes the routine at home, because the Rio Grande Valley rarely freezes hard enough to stop fly activity, and horses, cattle and wildlife keep moving all winter. Treat these months as the season to build the habit: a weekly wound check, prompt treatment of anything broken, a phone call when something looks wrong. That habit is the difference between an animal that heals and one that becomes part of next year's count.

Frequently Asked Questions

Can an indoor-only cat get screwworm?

The risk is low but not zero. A fly needs a minute and an open wound, and screens fail. If your cat has a scratch or a hot spot and a fly gets inside, inspect it daily and call a vet if the wound deepens instead of closing.

How do I tell screwworm larvae from ordinary maggots?

Blow-fly maggots work on dead or dying tissue, usually in a wound that was already dirty. Screwworm larvae feed on healthy flesh, so the wound gets deeper and more foul over a day or two instead of improving. Either way, call a vet; the worsening wound is the urgent one.

Do I need to worry about this in Dallas, Austin or Houston?

Confirmed cases this season have stayed in western and southern Texas counties, from the Rio Grande Valley to the Big Bend, and the sterile-fly barrier plus winter cold are meant to keep them there. Pay attention anyway: an untreated wound anywhere in the state is all a screwworm fly needs.

Is screwworm contagious between pets?

No. It does not pass from animal to animal; it spreads when flies lay eggs on a wound. An actively infested animal does attract more flies, so isolate it, cover the wound and get it to a vet rather than waiting to see what happens.

When to call a professional

Most screwworm prevention is wound management, and no pest control company can inspect your dog for you. What a licensed provider can do is reduce the fly, flea and tick pressure around the property — a big part of why a wound gets found at all. If you would rather hand that to someone who knows Gulf Coast and Hill Country insect pressure, find a licensed pest control company in Texas through our directory: 2,200-plus verified operators, searchable by county and service.