A parasitic fly that burrows into living flesh has been detected in the United States (US) for the first time in 60 years, prompting a quarantine zone along the Texas-Mexico border and plans to release millions of sterile insects.
The US Department of Agriculture (USDA) confirmed on Wednesday, 3 June 2026, that New World Screwworm was found in a three-week-old calf in La Pryor, Texas, about 48km from the southern border.
It is the first confirmed case in the US since 1966, with larvae discovered in the calf’s umbilical area.
Screwworm flies lay eggs in open wounds and mucous membranes of warm-blooded animals.
When the eggs hatch, hundreds of larvae feed on living tissue and can kill the host without treatment.
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Cattle ranchers have warned an outbreak could reduce herd sizes, cut beef production and push consumer prices higher.
On that note, the USDA and Texas authorities have established a 20km detection and quarantine zone around La Pryor to limit animal movement, the main way the parasite spreads.
The agency also said preparations are under way to release millions of sterile male screwworm flies.
Females mate only once, so unfertilised eggs will not hatch, a method previously used to eradicate the pest.
New World Screwworm has been advancing north through Mexico for the past year as cases rose in Central America.
US officials said containment efforts have delayed its arrival by about 12 months.
Agriculture Secretary Brooke Rollins said USDA personnel had arrived in South Texas to support operations and urged livestock producers to remain vigilant.
The agency stressed the fly poses no food safety risk and human infections remain rare, though the parasite can infest people and pets.
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