Smell of death could help trap invasive, cow-killing screwworms
Popular Science...
Humans are evolutionarily wired to despise certain smells for a good reason. Some distinctly disgusting odors like rotting flesh are often a byproduct of bacterial infection, something we generally hope to avoid as a species. But while these unappealing scents may revolt people, other creatures are irresistibly drawn to them.
“We use these bacterial cues to stay away from certain things—to not eat spoiled meat, for example,” Jessica Metcalf, a microbial ecologist at the University of Colorado, recently explained. “The insects are using them for a different reason. They’re like, ‘Yes, bring it, that smells like a great place to lay eggs.’”
Metcalf is currently focused on an insect whose fondness for stinky, unhygienic hotspots is once again causing problems in the United States: the New World screwworm blowfly (Cochliomyia hominivorax). The screwworm is attracted to open wounds in any warm-blooded animal, and this is particularly a problem for livestock including cattle, sheep, and goats. Eggs laid in these injuries will spawn maggots that feed on living tissue, often turning deadly for their hosts.
Ecologists effectively eradicated screwworm populations from the continental U.S. by 1966 using sterilization techniques developed during the mid-20th century. Unfortunately, the pests resurfaced in southern Mexico in 2024, and funding cuts overseen by the Department of Government Efficiency (DOGE) eliminated plans to combat the fly’s return. Texas confirmed the first new cases of screwworm infestation in the U.S. in over 50 years in June. Within weeks, observers confirmed additional examples in livestock and dogs elsewhere in the state, as well as in New Mexico.
The initial step in fighting the screwworm is monitoring for new outbreaks, and the easiest way to keep tabs on the insects is through baited lures. Many popular setups rely on scents produced by the bacteria in rotting meat. Unfortunately, screwworms are not the only organism drawn to the odor. A closely related, less dangerous, and more common blowfly called the secondary screwworm will also find their way into the traps, making it difficult for conservationists to accurately keep an eye on their targets.
Unlike the New World screwworm, its blowfly cousin prefers to dine on dead meat. Knowing this, Metcalf’s team is designing improved traps packed with tailored bait that mirrors bacterial odors only emitted in living tissues. To do this, they are identifying the specific volatile organic compounds that only entice New World screwworms.
It’s not only a host’s bacteria that attracts the bugs. Screwworms carry bacteria that infects their hosts and then signals fellow screwworms to join in on the meal. By pinpointing those microscopic organisms, Metcalf and her colleagues are further customizing their lures to not only draw screwworms, but divert even more of them away from livestock. The strategy hinges on the same science used by forensic investigators to determine a person’s time of death.
“It turns out we can also leverage decomposition ecology, which relies heavily on blowflies and their bacterial partners, to improve surveillance and control of the New World screwworm,” said Metcalf.
Although not yet nearly as widespread an issue as it once was, these and other methods are needed to keep the screwworm’s resurgence not only limited, but brief.
“Because we had been working on the relationship among insects, bacteria and animal decomposition for the last 15 years…we were well set up to tackle this problem,” she added.
The post Smell of death could help trap invasive, cow-killing screwworms appeared first on Popular Science.