Experts sound alarm on screwworm in cattle

Cattle ranchers and wildlife experts are sounding the alarm on a parasitic fly that lays eggs in the wounds of animals and humans, causing severe and sometimes fatal infections.

The fly called screwworm can eat a full-grown steer in 10 days.

The US eradicated the screwworm in 1966 by releasing sterile male flies, but the parasite still exists in Central and South America, posing a risk of spreading north.

US officials warn farmers and pet owners near the southern border to watch for symptoms in animals, including loss of appetite, odd behavior, head shaking, decay smells and isolation.

In November 2024, the US temporarily stopped importing Mexican livestock after an infected cow was found near Mexico’s border with Guatemala. Imports resumed in February after increased sterile fly releases and monitoring.

Tensions rose this April, when Mexico restricted American flights, dispersing sterile flies and imposed duties on equipment.

However, by the end of April, both countries reached an agreement to allow more flights and waive the duties, avoiding another livestock import ban.

According to the USDA, an infestation could cost the Texas economy $1.8 billion.