The U.S. Department of Agriculture is strengthening its defenses against New World screwworm (NWS) by shifting sterile insect dispersal operations closer to the U.S.–Mexico border.
The USDA’s Animal and Plant Health Inspection Service will redirect aircraft and sterile insect releases to reinforce coverage along the border. The new dispersal area extends about 50 miles into southern Texas near Tamaulipas, Mexico. Officials say the move will create a protective buffer if the pest continues to spread north.
“At the Secretary’s direction, protecting the United States from screwworm remains our highest priority,” said Dudley Hoskins, USDA Under Secretary of Marketing and Regulatory Programs. “Although the nearest active case in Mexico is still about 200 miles from the border, cases continue to spread in Tamaulipas. Shifting our operations now reduces risk before the threat moves closer.”
Sterile Fly Releases Target Reproduction
USDA continues to rely on sterile insect technique as a primary defense against screwworm. Female screwworm flies mate only once. When they mate with sterile males, they lay eggs that do not hatch. This process interrupts reproduction and slows the spread.
To stay ahead of the outbreak, USDA will release sterile flies north of current NWS cases in Mexico. The goal is to intercept any flies moving toward the U.S. border. Officials pair this strategy with surveillance, movement controls and producer outreach.
Because surveillance continues during releases, traps in Texas may capture sterile flies. To prevent confusion, USDA marks sterile flies with a fluorescent dye. The dye glows under ultraviolet light, allowing officials to quickly rule out wild screwworm.
Import Inspections Strengthen Protection
USDA officials also highlighted the role of import inspection protocols in protecting U.S. livestock.
Earlier this week, inspectors identified screwworm larvae on a horse presented for routine import at a Florida quarantine facility. Laboratory testing confirmed the larvae as NWS. Veterinarians treated the animal immediately and placed it in quarantine until follow-up exams confirm it is free of infestation.
Officials say the case does not appear linked to the outbreak in Mexico. However, the incident shows how existing protocols detect threats before they spread.
Surveillance Shows No U.S. Detections
USDA continues intensive surveillance along the southern border. Teams monitor 121 screwworm-specific traps across high-risk areas. They also rely on thousands of additional insect traps already in place.
To date, laboratories have tested more than 42,000 flies. None have tested positive for NWS.
APHIS Wildlife Services also inspects wildlife for signs of infestation. Teams have examined more than 9,300 animalsacross 39 species and 131 U.S. counties. So far, inspectors have found no evidence of screwworm.
Producers Asked to Remain Alert
Although USDA has not detected NWS in the United States, officials urge producers and animal owners to remain vigilant.
Signs of infestation include worsening or draining wounds, visible maggots, or eggs near wounds or body openings. These areas include the ears, nose, genital region and the navel of newborn animals.
Adult screwworm flies resemble slightly larger houseflies. They have metallic green or blue bodies, orange eyes and three dark stripes on their backs. The larvae feed on living tissue and can affect livestock, wildlife, pets and, in rare cases, people.
Producers who suspect screwworm should contact their state animal health official or USDA veterinarian immediately. Anyone with suspicious skin lesions should seek medical care.
More information about New World screwworm and USDA response efforts is available at Screwworm.gov.
