Rows of horses in individual stalls at a stable, with hay and feeding buckets, and a person in the background handling hay.

NEW WORLD SCREWWORM

Go Behind the Scenes

Inside NWS Inspections: A Veterinarian’s Perspective

See how Texas Racing Commission Veterinarians are working to detect, prevent, and respond to New World Screwworm at Texas Racetracks.

Know the Threat

Three larvae with segmented bodies on a white surface.

Closeup of three New World Screwworm larvae (maggots)

Source: Sohath Yusseff-Vanegas, USDA Agricultural Research Service

NWS Information & Resources

Close-up of a fly on a green leaf

Adult New World Screwworm Fly

Source: USDA-APHIS

  • New World screwworms (NWS) are parasitic flies (Cochliomyia hominivorax) that lay eggs in open wounds, genitalia or mucous membranes such as the nostrils, eyes or mouths of live warm-blooded animals.

    These eggs hatch into parasitic larvae (maggots) that only feed on living tissue, unlike other fly larvae that prefer dead or necrotic tissue. NWS larvae burrow or “screw” into living tissue with sharp mouth hooks, giving them a screw-like appearance. Infested wounds quickly become infected and, if left untreated, will kill infested animals.

    Common Areas of Infestation:

    ·       Newborn animals’ umbilical stump/navel

    ·       Mucous membranes- genitalia, eyes, nose, mouth

    ·       Wounds- cuts, scrapes, tick bites

    ·       Other Areas- castration, branding

    What an NWS Infestation Might Look Like:

    ·       Open wounds or sores with live maggots

    ·       Visible irritation/shaking heads

    ·       Foul, rotted flesh odor

  • “The most effective thing you can do is have eyes on your animal.”

    Monitor:

    ·       Check for flies, maggots, larvae, or eggs.

    ·       Check for foul smells or drainage in and around body openings.

    Isolate:

    ·       Animals with suspicious wounds or signs should not be moved from the current location Avoid moving animals from a pasture or premises, only pen or corral to prevent further spread Keep suspect animals in one area while you wait for collection to occur.

  • If you see live animals with maggots, report immediately. Early detection is imperative. Do not delay if you suspect an NWS infestation. Reporting is crucial to managing and eradicating an NWS infestation.

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    Livestock or Exotic Species

    Texas Animal Health Commission

    Contact a local TAHC Region Office:

    • Amarillo (806) 641-7000

    • Beeville (361) 358-3234

    • Giddings (979) 212-5440

    • Laredo (956) 568-5741

    • Stephenville (512) 556-6277

    • Sulphur Springs (903) 919-3748

    Operating Hours
    Monday-Friday: 8 a.m. - 5 p.m.

    On weekends, contact TAHC or the Veterinarian on Call 1-800-550-8242.

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    Humans

    Texas Department of State Health Services

    For suspected human cases, contact your regional zoonosis control veterinarian.


    NWS and Humans
    Zoonosis Control Contact Information

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    Domestic Pets

    Contact your local veterinarian.

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  • U.S. Department of Agriculture (USDA)

    Texas Animal Health Commission (TAHC)

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Diagram showing the life cycle of a fly, starting with an adult female laying eggs on open wounds of hosts like horses, cattle, sheep, goats, and dogs. The larvae hatch and burrow, feeding on flesh, then drop to the ground to pupate. Adult flies emerge and restart the cycle.

Current NWS Activity in Texas

The New World Screwworm Life Cycle