The Latest on the Screwworm

By NTFR Staff

For many years, most ranchers heard about New World screwworm only from older generations. It belonged to history books, old stories and warnings from veterinarians who remembered what it could do before the U.S. eradicated it.

That changed this summer. On June 3, 2026, the U.S. Department of Agriculture confirmed New World screwworm in a calf in Zavala County, Texas. Officials have reported additional detections in Texas since that first case, and state and federal agencies have responded with surveillance, movement restrictions in affected areas and sterile fly releases.

Common maggots feed on dead tissue. Screwworm larvae feed on the living tissue of warm-blooded animals, including cattle, horses, sheep, goats, dogs, wildlife and, rarely, people. The fly is attracted to open wounds and moist body openings. Even a small wound, such as a tick bite, castration site, dehorning wound, branding wound or newborn’s navel, can draw the female fly.

For North Texas producers, awareness is the key right now. You have no reason to panic, but you do have reason to pay close attention.

Check animals regularly for wounds, especially during fly season, and take any wound that seems to be getting worse instead of healing seriously. Warning signs can include a foul odor, visible larvae, bloody or watery discharge, swelling, pain, restlessness, head shaking, licking or animals separating themselves from the herd.

If you suspect screwworm, contact your veterinarian or animal health officials immediately. Early detection matters for the animal and for controlling the spread.

Ranchers and scientists have beaten this pest before. The sterile insect technique, which uses sterile male flies to interrupt reproduction, was the key to eradicating screwworm from the United States decades ago, and officials are using that same method again.

For now, North Texas livestock owners should inspect animals often, treat wounds promptly, follow any animal movement guidance from officials and report anything suspicious.

Screwworm is an old threat, and producers need to learn to recognize it again.