The Screwworm

The United States eradicated the New World screwworm in 1966. The program that achieved this involved releasing hundreds of millions of sterile male flies across the country so they would mate with fertile females and produce no offspring. This is called the Sterile Insect Technique. It took decades. It worked.

On Tuesday, the screwworm returned. The confirmed case is a three-week-old calf in La Pryor, Texas, thirty miles from the Mexican border. The calf is not responsible for the sixty-year setback. The calf is three weeks old.

(The New World screwworm is named for what it does. Its larvae screw. Into wounds. Of warm-blooded animals. The scientists who named it saw no reason to use a different word.)

The eradication in 1966 was considered a significant public health and agricultural achievement. The sterile-fly program cost millions of dollars and required the sustained, coordinated release of flies who could not reproduce. The fertile flies mated with the sterile flies. The offspring did not exist. The screwworm population collapsed. It stayed collapsed for sixty years.

It stayed collapsed for sixty years and approximately six months.

The USDA is now investigating the La Pryor case and considering its options. The most obvious option is more sterile flies. The agency that invented the sterile-fly solution presumably still knows how to make sterile flies. The sterile flies presumably still cannot reproduce. This is expected to continue.

The calf is being treated. Its role in the history of North American pest eradication was not something it pursued. It was three weeks old when this happened and had not yet developed a position on any of it.

This is, overall, a manageable situation. The screwworm was beaten once. It can be beaten again. The main cost is acknowledging that "eradicated" and "gone forever" are different words with different meanings, a distinction that was not relevant for sixty years and is now relevant again.