New World Screwworm in Horses: What the 2026 Texas and New Mexico Cases Mean for Your Barn

New World screwworm in horses: what just happened

New World screwworm in horses is an infestation of flesh-eating fly larvae in a wound, and in September 2026 it was confirmed in two U.S. horses: a working ranch horse in Presidio County, Texas, and a ranch horse near Mimbres in Grant County, New Mexico. The risk is concentrated in parts of West and South Texas and southwest New Mexico, but anyone who hauls through the region, or buys horses from it, should know the signs.

The Texas case was found on Sept. 9 in a wound on one hind leg, and US Equestrian called it the first equine screwworm case in the United States this century. The New Mexico horse was identified on Sept. 17 with a leg wound. It is New Mexico's second case of this outbreak, after a dog in Lea County in June.

For scale, Houston Public Media's case tracker counted 50 confirmed U.S. cases as of Sept. 21, all since June: 48 in Texas and 2 in New Mexico. Texas alone has counted 39 affected premises across 17 counties.

What is New World screwworm?

Despite the name, it isn't a worm. New World screwworm (Cochliomyia hominivorax) is the maggot of a fly, and unlike most maggots it eats living tissue, not dead tissue.

The life cycle explains why owners need to move fast:

1. A female fly lays a cluster of eggs, up to several hundred at a time, at the edge of a wound or on moist membranes like the eyes and nostrils.
2. The eggs hatch within 10 to 12 hours.
3. The larvae feed for about a week, tearing deeper into the flesh with hooked mouthparts. Rings of tiny spines give them their screw-like look.
4. They drop to the ground, pupate and become new flies, ready to find the next wound.

A small cut that looked fine on Monday can be an active infestation by midweek. The flies don't pick a species, either: cattle, horses, dogs, wildlife and people can all be infested.

The United States wiped out screwworm decades ago by releasing sterile flies, and the same method is in use now. Agriculture Secretary Brooke Rollins has said USDA has put more than $1.3 billion into the response, including the release of more than 1 billion sterile flies.

Screwworm symptoms in horses: where and what to check

Both 2026 horse cases involved leg wounds, but flies go after any wound or moist opening. Build a quick daily check into feeding time or grooming.

Where to look

• Legs: cuts, scrapes, wire wounds and rubs, including the small ones you'd normally ignore
• Surgical sites: castration incisions and any stitched or healing wound
• Foals: the navel (umbilical area), every day
• Moist areas: eyes, nostrils, lips, sheath or udder, and under the tail

Warning signs

• A wound that gets bigger, deeper or wetter instead of healing
• A foul smell, or fluid draining from the wound
• Visible maggots in or around the wound
• Swelling around a wound
• The horse licking, biting or rubbing at one spot, or acting unusual around it

You can't reliably tell screwworm from ordinary blowfly maggots by eye. Lab confirmation relies on features you'd need a microscope to see, so treat any maggots in a living horse's wound as a vet call.

The 2-minute wound check

1. Check at the same time every day, so a change jumps out.
2. Run your hands down every leg, feeling for heat, swelling or wet, sticky spots.
3. Look at the eyes, nostrils and lips.
4. Check the belly, sheath or udder, and under the tail.
5. Take a dated phone photo of any wound so you can compare tomorrow.

Our health basics page covers normal vital signs, which help when you describe a problem to your vet.

Found maggots in a wound? Who to call

1. Call your veterinarian right away. Don't wait a day to see if it improves. Your vet reports suspected cases to state animal health officials.
2. Keep the horse where it is. Don't haul it anywhere until your vet or state officials say so.
3. Don't treat the wound yourself. Screwworm treatment uses products authorized for it, chosen by your vet. If officials ask you to collect larvae for testing, follow their instructions exactly.
4. Photograph the wound and check your other animals, including dogs, the same day.

Reporting contacts

• Texas: your Texas Animal Health Commission (TAHC) region office, or TAHC's reporting line at 1-800-550-8242
• New Mexico: the New Mexico Livestock Board, state veterinarian's office (505) 841-6161, or ScrewwormNM.org
• Other states: your veterinarian, who contacts your state veterinarian and USDA APHIS
• People: if you find maggots in your own wound, see a healthcare provider

Horse travel restrictions: screwworm rules for hauling and shows

Zones are drawn, redrawn and released often. Check the rules the day before you haul, not the week before.

Texas

All warm-blooded animals in a Texas infested zone need TAHC authorization before leaving. Expect an inspection and an NWS movement and treatment certificate listing the product used and the animal's official ID; inspection requests go to 512-714-1936. As of Sept. 23, zones covered parts of Brewster, Crockett, Edwards, Jeff Davis, Pecos, Presidio, Schleicher, Starr, Sutton, Terrell, Val Verde and Zapata counties.

New Mexico

Around the Grant County horse, officials are setting an infested zone of at least 12.4 miles (20 km), plus a wider surveillance zone. Animals inside the infested zone must be inspected, and treated if needed, before moving within or out of it. Beyond that, officials say routine trips to the vet, fairs, sales or recreational rides generally aren't restricted unless an inspector flags a higher-risk situation, such as an open wound.

Other states and the border

Georgia re-imposed enhanced entry requirements for all warm-blooded animals from Catron, Hidalgo, Luna and Sierra counties and parts of Grant County, and it applies the same rules to animals from Texas: a certificate of veterinary inspection, issued within 7 days of travel, stating the animal was inspected and found free of screwworm. Animals coming from an infested zone also need a Georgia entry permit, requested at least 48 hours ahead. Other states can add rules quickly, so call the destination state veterinarian's office before you go. The American Horse Council says horses still can't cross the U.S.-Mexico land border in either direction. Cattle imports from Mexico are restarting port by port: USDA reopened Douglas, Arizona, to Mexican cattle on Aug. 24, and the Santa Teresa reopening scheduled for Sept. 24 is for cattle too. USDA says it may later consider horses at Santa Teresa and Columbus, New Mexico, but hasn't set a date.

Shows and events

At US Equestrian-licensed competitions, horses coming from a state with confirmed screwworm must be checked for wounds on arrival before they can enter the stabling area, and that includes horses hauling in for the day. Depending on the states involved, you may also need a documented veterinary inspection before you leave, on arrival, or both. If your horse has a wound, or a surgical incision a week old or less, bring vet records or a note on the health certificate showing it was treated with an FDA-authorized screwworm product.

Hauling checklist

• Current entry rules for your destination state
• Health certificate, current Coggins and any screwworm inspection paperwork
• Wound check before loading and again on arrival
• Fly mask and fly sheet for the trip
• Your vet's number and the state veterinarian's number saved in your phone

More on getting ready for events is in our show prep guide.

How to lower the risk in your barn

• Treat every wound promptly with your vet's guidance, and keep it clean and covered.
• Use vet-directed fly control plus physical barriers such as fly masks and fly sheets.
• Pick up manure often and get rid of standing water where flies breed.
• Fix what causes cuts: loose wire, protruding nails, broken boards. Our barn safety page has a walk-through.
• Ask about timing of elective procedures like castration if you're in or near a zone.
• Inspect new arrivals from Texas or New Mexico the day they unload.

For the bigger daily routine, see our horse care guide.

What to watch next

• Zone changes. Texas has been releasing some zones while adding others, like the Presidio and Jeff Davis area. Check TAHC's map and ScrewwormNM.org before any trip.
• More state entry rules. Georgia's quick move shows destination rules can change within days of a new case.
• Santa Teresa on Sept. 24. USDA plans to reopen the port to Mexican cattle, with pre-inspection in Chihuahua and inspection on arrival. Horses are not included.
• Fall show season. If your horse comes from an affected state, expect a wound check on arrival, and build extra time into check-in.
• Warm days. Flies stay active while the weather is warm, so keep up daily checks until your vet says local risk has dropped.

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