The Smell of Trouble: Scientists Decode Wound Odors to Build a Better Screwworm Trap

Jessica Metcalf's work stinks. Literally. And in the fight against the New World screwworm now established in Texas, that may turn out to be exactly what the livestock industry needs.

The Colorado State University professor is leading a USDA-funded project to decode the foul-smelling chemistry of open wounds — the bacterial byproducts that tell a screwworm fly it has found the perfect place to lay its eggs. The goal is a new generation of trap lures tuned specifically to Cochliomyia hominivorax, the flesh-eating parasite that has turned up in Texas cattle, sheep, goats and dogs since early June.

The project tackles a quiet weakness in the surveillance system the entire containment effort depends on. One of the most widely used lures relies on the smell of rotting meat — which happens to be irresistible to the secondary screwworm, a close relative that prefers dead flesh and does no harm to living animals. Traps fill up with the wrong fly, and the dangerous one can slip past unnoticed. Metcalf's team wants to separate the two by their noses: identifying the volatile organic compounds, produced by wound bacteria, that attract the New World screwworm to living tissue rather than carrion.

"The insects are using them for a different reason," Metcalf said of the same bacterial odors that make humans recoil. "They're like, 'Yes, bring it, that smells like a great place to lay eggs.'"

The work grows out of fifteen years of decomposition research at the team's main field site in Huntsville, Texas, where Metcalf and her collaborators have mapped the microbial ecology of decaying animals — science with forensic applications, since the microbes on a body can pin down time of death. The New World screwworm, which evolved from a carrion-feeding ancestor, turned out to be a natural extension of that expertise. The team, including CSU faculty Kayla Borton and Kelly Wrighton, will run genomic and chemical analyses through the Colorado State Microbiome Network, comparing bacteria and odors from wounds against samples from dead animals. Blowflies also carry their own bacterial partners, which signal suitable hosts to other flies — another layer the researchers hope to exploit, potentially even to redirect the pest away from live animals.

Science this specialized still needs boots on the ground. The project is recruiting livestock producers, veterinarians and wildlife biologists to swab animal wounds and ship samples to the lab, with collaborators in Texas, Arizona and New Mexico running parallel outreach. Tracey Goldstein, director of CSU's One Health Institute, is coordinating the network — and she argues it cannot be wide enough. "This particular fly doesn't care if you're a person, a deer, a pig or a chicken. It will infest everything, which is a little scary," she said. "We really need all eyes and ears out there on the ground."

That message resonates in the cattle industry, where movement restrictions in infested Texas counties require every animal to be inspected and every wound healed before transport. "We can't treat our way out of this problem," said Julia Herman, a beef cattle specialist veterinarian with the National Cattlemen's Beef Association, who will connect producers nationwide with the research. "We have to have other ways to manage this fly, and this project provides a critical piece."

Metcalf's grant is one of 40 projects funded under USDA's $105 million NWS Grand Challenge, the same initiative backing electron-beam sterilization work at Texas A&M and the agency's new male-only NovoFly strain. Detection may lack the drama of aerial sterile fly drops, but every eradication milestone in the program depends on it: you cannot flood a zone with sterile flies, or lift a quarantine, until you know precisely where the enemy is. A lure that ignores the harmless cousin and calls in only the killer would make that map far sharper — for Texas first, and for every state watching the outbreak nervously from north of the quarantine line.