Livestock-killing pest pushes US to breed billions of flies to combat spread

The US government is preparing an ambitious and unconventional plan to combat a deadly pest: breeding billions of sterilized flies and releasing them from airplanes over southern Texas and Mexico. This effort targets the New World Screwworm fly, a flesh-eating insect whose larvae can severely harm or kill livestock, wildlife, pets, and even humans. The operation aims to protect the beef industry and animal health by preventing the reestablishment of this dangerous parasite.

The New World Screwworm fly is a rare type of maggot that feeds on live tissue, unlike most fly larvae that consume dead flesh. Female screwworm flies lay their eggs in open wounds or mucus membranes of warm-blooded animals. An article published by AP reporting on the government's unusual plan to tackle this problem points out that the larvae burrow into the flesh, often leading to severe infections once the eggs hatch. If left untreated, this can be fatal. “A thousand-pound bovine can be dead from this in two weeks,” said Michael Bailey of the American Veterinary Medicine Association.

To eliminate this threat, the US Department of Agriculture (USDA) is reviving an effective technique first used in the 20th century: the release of sterilized male screwworm flies. These males, irradiated to render them infertile, mate with wild females. Since females only mate once in their lifetime, the resulting unfertilized eggs do not hatch, causing the population to gradually collapse.

This method is both effective and environmentally safe compared to chemical spraying. It was successfully used in the 1960s and 1970s when the US and Mexico released over 94 billion sterile flies to eradicate the pest from North America. However, the screwworm has reemerged in southern Mexico, prompting the USDA to prepare for large-scale intervention once more.

Currently, sterile flies are bred at a facility in Panama, which can produce 117 million per week. The USDA plans to increase production capacity to 400 million per week to ensure sufficient coverage. This includes spending $21 million to upgrade a fruit fly facility in southern Mexico and $8.5 million to establish a new distribution center in Texas. A new factory in Mexico is expected to begin operations by July 2026.

The logistics of fly release have evolved slightly since the 1950s, but the core method remains the same. Planes drop crates of flies over affected areas. However, the operation is not without risks—last month, a plane crashed during a fly-release mission near Guatemala, resulting in three deaths.

Concerns over the fly’s northward spread have already impacted trade. In May, the US temporarily halted live animal imports from Mexico, including cattle, horses, and bison. The border is not expected to fully reopen until at least mid-September.

Despite past success, experts like Edwin Burgess of the University of Florida caution against complacency. He praised the sterile fly technique as one of the USDA’s “crowning achievements,” but warned that “something we think we have complete control over... can always rear its ugly head again.” As such, some officials argue the new fly factories should remain operational indefinitely to ensure the pest doesn’t return.

By Nazrin Sadigova