The new world screwworm once caused widespread devastation to livestock in the United States, prompting a decades-long eradication effort. Today, scientists in California are taking proactive steps to make sure history doesn’t repeat itself.
Despite its name, the screwworm isn’t a worm at all. It’s the larval stage of a metallic blowfly that behaves differently from most related species. While many blowflies help break down dead animals, this one feeds on living flesh. It lays eggs in open wounds. When the larvae hatch, they burrow into tissue, enlarging injuries and potentially causing fatal infections.
The screwworm was once widespread across California and much of the southern United States. It was eliminated about 60 years ago through the release of millions of sterile male flies. Because females mate only once, the population collapsed, driving the species far south, where a control barrier has long been maintained in Panama.
But in recent years, the fly has reappeared in parts of Central America and Mexico, likely spread through the movement of infested animals. Climate change may also be a factor, as warmer temperatures and milder winters expand the regions where it can survive. Although it has not yet returned to the United States, it has been found in northern Mexico within 70 miles of the Texas border.
To prepare, scientists at the University of California Riverside are deploying monitoring traps across the state using specialized lures designed to attract the screwworm. Awareness, early detection, and proven control methods remain the best tools to protect agriculture and prevent another costly outbreak.
