US Deploys Sterile Flies and Sniffer Dogs to Counter Flesh‑Eating Screwworms

Fri Jul 10 2026 17:02:57 GMT+0000 (Coordinated Universal Time)

After a 60‑year hiatus, the New World Screwworm has appeared in Texas. Officials are releasing millions of sterilised flies, setting up quarantine zones and stationing dogs at borders in an effort to stop the parasite from spreading to cattle and humans.

The arrival of the New World Screwworm in Texas marks the first outbreak in the United States since 1966. A three‑week‑old calf in La Pryor, Texas, was the first confirmed case when larvae were found in its umbilical cord. The parasite, which lays eggs in wounds of warm‑blooded animals and burrows through flesh, poses a serious risk to livestock and, in rare instances, to humans. To combat the threat, the USDA and USDA‑AP (formerly USAID) have announced a coordinated response that includes releasing hundreds of millions of sterile flies using the Sterile Insect Technique, establishing a 20 km control zone around the infection site, and deploying specialized sniffer dogs (the “Beagle Brigade”) at borders. Criticised for a slow response and for not meeting the required fly‑production capacity, the government is now building new facilities to produce up to 600 million sterile flies weekly – a figure far beyond the current 100 million capacity. While officials say the infestation has not yet reached full establishment in the U.S., farmers in Texas urge vigilance – covering wounds on livestock and reporting any signs of the parasite. Political tensions have flared as Treasury and border officials investigate alleged under‑investment and “open‑border” policies that may have facilitated the flies’ northward migration. Climate change may also be pushing the insect further south than its historic tropical range.

US Deploys Sterile Flies and Sniffer Dogs to Counter Flesh‑Eating Screwworms

The New World Screwworm has re‑appeared in the United States after a 60‑year absence, with the first confirmed case in Texas discovered in a three‑week‑old calf. The parasite is dangerous to cattle and can cause painful infections in humans.

Reuters A larvae with a black background

The USDA announced a multi‑pronged plan to stop the parasite. The strategy relies heavily on the Sterile Insect Technique, in which millions of genetically‑altered, sterilised flies are released to mate with wild females, thereby producing infertile eggs that fail to hatch.

Officials will need to produce about 600 million sterile flies every week to match the projected growth of the New World Screwworm. Current facilities in the U.S. and Mexico can produce only about 100 million per week.

Getty Images A screwworm fly seen in extreme close up

In addition to fly releases, a 20‑kilometre “control zone” around the detection point has been established, with strict movement controls and surveillance. The “Beagle Brigade” – a team of specially trained dogs – has been positioned at U.S. borders to sniff out screwworms and prevent them from crossing into the country.

Getty Images A beagle with a vest sniffs luggage

Despite these efforts, critics – including Texas ranchers – accuse the federal response of being slow and insufficient, pointing out that the current fly‑production can not keep pace with the parasite’s spread. The political debate has highlighted claims that prior administration cut funding for screwworm‑tracking programmes in Latin America and that open‑border policies have facilitated the insect’s entrance into U.S. soil.

With climate change nudging the screwworm further north and a recent surge in cases across Central America, stakeholders are urging vigilance: farmers must cover animal wounds, anyone who notices unusual swellings on pets or themselves should report immediately, and officials are keeping a close eye on the effectiveness of the sterile fly and dog‑scenting tactics.