US Faces Renewed Screwworm Threat to Livestock Amid Historical Lessons

WHO:

The Texas Tribune - Edward F. Knipling, lead entomologist; Raymond Bushland, scientist; B.A. Bitter, veterinarian; U.S. Secretary of Agriculture Earl Butz; Mexican Secretary of Agriculture Manuel Bernardo Aguirre.

Bloomberg - Department of Government Efficiency (DOGE); USDA (United States Department of Agriculture).

WHAT:

The Texas Tribune - The New World screwworm has entered the U.S., with cases continuing to increase.

The Texas Tribune - The USDA estimates that the industry saved more than $900 million a year due to past eradication efforts.

The Texas Tribune - In 1935, 180,000 livestock deaths from the screwworm were reported in under half of Texas’ counties.

The Texas Tribune - In 1976, producers spent $132.1 million in response to the screwworm, with total economic loss for Texas that year nearing $330 million.

The Texas Tribune - By 1972, Texas confirmed 90,000 cases of screwworm, a significant increase from 444 the previous year.

WHERE:

The Texas Tribune - The outbreak has affected livestock in the U.S., particularly in Texas and Florida.

The Texas Tribune - The sterile fly production plant was located at the Former Moore Air Force Base near Mission, Texas.

The Texas Tribune - Curacao, an island 40 miles from Venezuela, was used as a testing area for the Sterile Insect Technique.

WHEN:

The Texas Tribune - The USDA declared the U.S. free of indigenous screwworms in 1966.

The Texas Tribune - By 1980, northern Mexico states were free of screwworms, and the last case in the U.S. was reported two years later.

The Texas Tribune - In 1967, Texas recorded 835 cases of screwworm in 67 counties.

WHY:

The Texas Tribune - The re-emergence of the screwworm followed years of warnings from Central America and Mexico officials about an impending outbreak.

The Texas Tribune - The financial impact of the current outbreak is still unknown, but historical outbreaks have shown significant economic consequences.

HOW:

The Texas Tribune - The Sterile Insect Technique was developed by Knipling and Bushland, involving the release of sterilized flies to control screwworm populations.

The Texas Tribune - Smear 62, a treatment developed by Knipling, could kill all screwworms in a wound up to the size of half a dollar and protect against reinfestation.

(UPDATED June 26, 2026 04:25 UTC)

The New World screwworm has made its way into the U.S., with increasing cases reported, particularly affecting livestock in Texas and Florida. The USDA estimates that the industry previously saved over $900 million annually due to past eradication efforts, but the financial impact of the current outbreak remains unknown. Developed by Edward F. Knipling and Raymond Bushland, the Sterile Insect Technique involves releasing sterilized flies to control screwworm populations, while a treatment called Smear 62 can kill screwworms in wounds and prevent reinfestation.