New World screwworm (NWS) is a fly whose maggots eat living flesh. Ordinary blowfly maggots feed on dead tissue. The female lays her eggs in an open wound or a body opening. The maggots burrow in and make the wound bigger. Left untreated, an animal can die within about a week.
It can strike any warm-blooded animal: cattle, sheep, goats, horses, dogs, wildlife and, rarely, people. USDA says it is not a food safety issue.
Where things stand (as of Oct. 18, 2026)
This section changes. Check the state links below for today's status.
- Texas: First confirmed June 3, 2026, in a calf in Zavala County. TAHC reports 17 counties with confirmed detections and 43 premises. Movement restrictions remain in infested zones in parts of Brewster, Crockett, Edwards, Jeff Davis, Pecos, Presidio, Schleicher, Starr, Sutton, Terrell, Val Verde and Zapata counties. Several zones have since been released.
- New Mexico: First confirmed June 7, 2026, in a dog in Lea County. On Oct. 16, 2026, officials reported two new cases (a calf and a horse) in Grant County.
- Oklahoma: ODAFF reports no confirmed case.
- Kansas: KDA lists cases in Texas and New Mexico. Its page does not report a Kansas case.
Sterile-fly releases, the method that wiped out screwworm in the U.S. in 1966, are under way in affected areas.
Signs to look for
- A wound that won't heal or keeps getting worse
- Maggots in a wound, often cream-colored, packed in deep
- A foul smell, bloody or draining discharge, swelling
- An animal licking or biting at a spot, shaking its head, going off by itself, or going off feed
- In newborns: a wet, swollen or smelly navel
High-risk wounds include fresh navels, castration and dehorning cuts, branding, tick bites, barbed-wire cuts, shearing nicks and deer antler velvet.
Prevention on the place
- Check animals often, especially after calving and working cattle.
- Keep wounds clean and covered. Treat working wounds the same day.
- Work with your veterinarian. The FDA has approved or authorized several products to prevent or treat screwworm in livestock. Follow the label and the withdrawal times before anything goes to slaughter or milk.
- Think about timing. If you can, do castration and other cutting in cooler, low-fly weeks. Keep an eye on the wounds afterward.
- Inspect animals before you haul them, and check pets and trailers if you've been in an infested area.
Oklahoma's agriculture department advises not to self-treat a suspected case before talking to a veterinarian or state official. They need a larva sample to confirm it.
Who to call if you suspect it
Screwworm is reportable. Report it right away. Texas asks for reports within 24 hours of suspicion.
| State | Livestock and pets | Notes |
|---|---|---|
| Texas | TAHC, 1-800-550-8242 (veterinarian on call) or your TAHC region office | Wildlife: Texas Parks and Wildlife, 512-389-4505 |
| Oklahoma | ODAFF State Veterinarian, 405-522-6141 | Online report form at ag.ok.gov/nws. Your OSU Extension office has sampling kits. |
| Kansas | KDA Division of Animal Health, 785-564-6601 | Or call your local veterinarian |
| New Mexico | New Mexico Livestock Board, 505-841-6161 | After hours: AgroGuard Hotline, 1-800-525-2782. NMSU Extension offices have sampling kits. |
Other states: see USDA's "Report Suspected Cases" page. General questions: [email protected].
Moving animals
- Out of a Texas infested zone: warm-blooded animals need prior approval from TAHC. That means an inspection, and a movement/treatment certificate from TAHC or a NWS Certified Inspector. To schedule TAHC inspectors in the zones, call 512-714-1936.
- Into Oklahoma or Kansas from an infested zone: you must meet the origin state's rules, get a permit from the receiving state's animal health official, and carry a certificate of veterinary inspection (CVI). The CVI must state that all animals listed were individually inspected and found free of wounds.
- Into Oklahoma from a surveillance zone: you need a CVI issued within 5 days of the move, with the same "free of wounds" statement.
Rules change as zones open and close. Call the receiving state before you haul.
If you lose animals
Ask your county FSA (Farm Service Agency) office whether your death losses qualify under the Livestock Indemnity Program (LIP). Keep vet records, dated photos and death records.
Cownty can text you when screwworm zones or movement rules change near your county.
Cownty is an independent service and is not affiliated with USDA, TAHC or any state agency. This is general information. Follow your veterinarian's and state animal health officials' directions.
See it for your county
Check your county
Every county, by state: Texas · Oklahoma · Kansas · New Mexico
Official sources
- Texas Animal Health Commission (TAHC) – New World Screwworm
- USDA APHIS – Screwworm.gov
- USDA APHIS – Report Suspected Cases of Screwworm
- Oklahoma Dept. of Agriculture, Food and Forestry (ODAFF) – New World Screwworm
- Kansas Department of Agriculture – New World Screwworm
- ScrewwormNM.org (New Mexico Livestock Board / NMDA partners)
- NMDA – State confirms first New World screwworm case in Lea County (June 9, 2026)
Rules and dates checked against these pages on Oct 18, 2026. Information only, not legal, tax, insurance or financial advice: the agency decides. Not affiliated with USDA or any government agency.