By Glenda Dvorak
What is New World Screwworm?
The New World screwworm (Cochliomyia hominivorax) is not actually a worm but a fly whose larvae (maggots) feed on the living tissue of warm-blooded animals. Cattle, sheep, goats, horses, swine, pets, wildlife, and even humans can be affected. Unlike most fly larvae, which feed on dead tissue or decaying organic matter, NWS larvae attack healthy living tissue.
Female NWS flies lay eggs in wounds, scratches, or natural body openings. A single female can lay up to 300 eggs at one time and as many as 3,000 eggs during her lifetime. Common sites include branding, dehorning, and castration wounds, as well as the umbilical cord of newborn animals. Even minor wounds, such as tick bites, can attract egg-laying flies.
The eggs hatch into larvae within 12-24 hours, and the larvae immediately begin feeding on the animal’s tissue. Over the next five to seven days, the infestation expands, causing severe tissue damage that can lead to secondary infections, debilitation, and even death if untreated. Mature larvae then drop to the ground, pupate in the soil, and emerge as adult flies. Under favorable conditions, the entire life cycle can be completed in about three weeks.
NWS was eradicated from the United States in 1966, but remained present in parts of Central and South America and Mexico. In June 2026, the pest spread northward and was detected again in the United States; as of July 10, 2026, the U.S. has recorded more than 30 infestations in Texas and New Mexico. Federal and state agencies are working to control, contain, and eradicate the pest.
How to Protect Your Animals
Early detection is critical! Routinely inspect animals for wounds and carefully check body openings such as the eyes, ears, nose, mouth, and genital areas. Pay particular attention to newborn animals and animals recovering from injury or surgery.
Source : iastate.edu