Screwworm Returns to Texas. Here's What to Know

The moment Texas cattle ranchers have feared for a while is here: The screwworm parasite has moved across the border from Mexico and shown up in South Texas. What to know about the New World screwworm, a type of blowfly:

• In Texas, the parasite turned up in a 3-week-old calf in Zavala County, and health authorities have put a 12-mile quarantine in effect. The USDA has warned that a widespread outbreak could cost Texas ranchers about $730 million and deliver a $1.8 billion loss to the state economy. It would also likely raise already high beef prices, reports NBC News.
• The fly's larvae feed on the living tissue of animals, and the parasite mostly affects cattle, pets, and wildlife, reports the Washington Post. Human infections are rare and typically involve people with untreated wounds or close exposure to infested animals. Maryland logged a case last year, that of a man who had traveled to El Salvador.
• The US eradicated the New World screwworm back in the 1960s, but it survived elsewhere, mostly in South America and in the Caribbean. The US also had a renewed outbreak in the early 1970s, notes the Texas Tribune. Scientists have been tracking its spread in Central America and into Mexico since 2023.

• The female flies are drawn to wounds, even tiny ones, where they lay their eggs, up to 3,000 over a 30-day lifespan. The eggs turn into maggots that burrow into the host's flesh, eventually dropping into the soil before emerging as adult screwworm flies. Even if the animal survives, it usually suffers damage to its hide and overall health, per the Tribune.
• The US previously released millions of sterile flies in Texas in a bid to curb the spread, and it stopped allowing Mexican cattle into the country. But Texas Agriculture Commissioner Sid Miller complained on Wednesday that it hasn't been enough. "For months, the screwworm has advanced rapidly through Mexico in spite of the USDA's existing game plan," he said, adding that "instead of using every available tool, USDA moved too slowly and relied solely on a partial solution that takes years to fully implement." He implored President Trump to get involved and "throw every available federal resource at this threat before it becomes a full-blown agricultural disaster."