Texas government confirms case, reviving ranchers’ old fears of New World screwworm

The return of the New World screwworm has revived an old fear among ranchers and rural communities in southern Texas. Texas Parks and Wildlife confirmed the parasite in a three-week-old calf with an umbilical lesion in Zavala County on June 3, 2026.

The screwworm is the larval stage of a fly that lays eggs in open wounds or body openings of living animals. Once they hatch, the larvae feed on living tissue, causing severe injury or death. The Texas Animal Health Commission said the parasite mainly affects livestock, but can also infest mammals, birds and, in rare cases, humans.

The danger has particular resonance in the region. Veterinarian Gaylon Wilmeth-Burleson of Dilley told Texas Public Radio that older generations still remember the damage caused by earlier infestations. “My father can tell me stories from when he was a child: we didn’t have many deer down here anymore because of screwworm infestations,” he said.

The concern comes during southern Texas’s deer-breeding season. Wilmeth-Burleson said fawns can become infected through the umbilical area, much like newborn calves.

Authorities are asking the public to watch warm-blooded animals and report possible infestations. Texas Parks and Wildlife Executive Director David Yoskowitz warned that screwworm could have devastating effects on free-ranging wildlife and rural communities. The first case is considered inactive, while state and federal partners conduct surveillance and epidemiological research, restrict animal movement and respond in infested areas. The United States last eradicated screwworm in 1966 using sterile insects, a method now being used again in affected areas.

The Texas Department of State Health Services said human cases are rare, but urged people to seek immediate attention for painful, foul-smelling wounds or visible larvae. It also said the parasite does not spread from person to person and that Texas’s food supply is safe.

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My father can tell me stories from when he was a child: we didn’t have many deer down here anymore because of screwworm infestations.