Flesh-Eating Maggots

 WHAT?

US to Release Billions of Radiation-Treated Flies to Stop Flesh-Eating Maggots

Screwworm larva with tusk-like mandibles visible
Screwworm larva with tusk-like mandibles visible. Credit: Animal and Plant Health Inspection Service / USDA

The US government is preparing a large-scale effort to combat a dangerous parasite by releasing billions of radiation-treated flies over southern Texas and parts of Mexico. The mission aims to stop the spread of flesh-eating maggots that threaten livestock, wildlife, and pets – and, in rare cases, humans.

The target is the New World screwworm fly, whose larvae burrow into the flesh of living animals, causing serious and often fatal injuries. The pest was eradicated from North and Central America decades ago, but it reappeared in southern Mexico late last year, raising fresh alarms.

Sterile flies to stop reproduction in the wild

To prevent the spread of the screwworm fly north, the U.S. Department of Agriculture (USDA) will breed male screwworm flies in secure facilities, sterilize them using radiation, and release them from aircraft. Sterile males mate with wild females but produce no offspring. Over time, the population declines and collapses. “It’s an exceptionally good technology,” said Edwin Burgess, a professor at the University of Florida. “It’s an all-time great in terms of translating science to solve some kind of large problem.”

Historic method gets renewed urgency

The method is not new. Between 1962 and 1975, the U.S. and Mexico released over 94 billion sterile flies to eliminate the pest. A facility in Panama has since maintained production, releasing up to 117 million sterile flies weekly to keep the fly in check. But with the recent resurgence, the USDA plans to raise that capacity to 400 million per week. The agency will invest $8.5 million to build a fly distribution center in southern Texas by the end of this year and another $21 million to convert a facility in southern Mexico to focus on screwworm flies. A full breeding facility is expected to be operational there by July 2026.

Flies pose a severe risk to animals, and sometimes people

The screwworm fly, known scientifically as Cochliomyia hominivorax, roughly translates to “man-eater,” according to the USDA. Unlike most fly species that feed on dead tissue, this one targets live flesh. Female flies lay eggs in open wounds or on moist tissue. “A thousand-pound bovine can be dead from this in two weeks,” said Michael Bailey, president-elect of the American Veterinary Medical Association.

Although veterinarians can treat infected animals, the condition causes severe pain. Don Hineman, a retired Kansas rancher, remembers the impact from his youth. “It smelled nasty,” he said. “Like rotting meat.”

Feeding, security, and safety pose challenges

Breeding the flies is complex. Females must be prompted to lay eggs, and larvae need nutrient-rich diets. In the past, horse meat and honey were used; however, today’s labs use blends of egg powder and cattle blood.

In nature, larvae drop to the ground to develop into adults. In the lab, workers replicate this with sawdust trays. Strict precautions are taken to prevent any fertile flies from escaping. Aerial release, while effective, carries risks. Last month, a plane dropping sterile flies crashed near the Guatemala border, killing three people.

Despite the challenges, experts stress that preparedness is key. “Something we think we have complete control over – can always rear its ugly head again” Burgess said. 

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