The tiny Galapagos Islands are a treasure trove of biodiversity, perhaps the best place on Earth to observe evolution in action. It also happens to be a war zone. All land birds, including two endangered species of Darwin’s finches, are fighting a losing battle to a species of parasitic flies likely introduced to the island from the mainland in the 1990s. To give the endangered birds an edge, scientists from the University of Utah are breaking with the Geneva Conventions and deploying chemical weaponry – namely, pesticide-soaked cotton balls.

When scientists distribute cotton balls soaked in permethrin – the same chemical found in de-lousing shampoo that’s also safe for the birds – finches collect and use them to build their nests. The chemicals kill off the fly larvae, which would otherwise infest and eventually kill newborns too weak to ward them off. Because the flies are an invasive species, there’s presently no way for the natives to repel them without outside assistance.

“Self-fumigation is important because there currently are no other methods to control this parasite,” blood-sucking maggots of the nest fly Philornis downsi, says University of Utah biology doctoral student Sarah Knutie, the study’s first author.

Knutie got the idea for the new study four years ago at her dorm in the Galapagos when she noticed Darwin’s finches “were coming to my laundry line, grabbing frayed fibers from the line and taking it away, presumably back to their nests,” she recalls. The birds also collect toilet paper, string and fibers from towels.

Since scientists knew that spraying nesting sites with a 1% permethrin solution destroyed virtually all maggots, Knutie wondered if the birds couldn’t be encouraged to do it themselves. They dispersed cotton balls soaked in the solution alongside untreated balls as a control. They found that the birds displayed no preference for either ball, giving them the green light to spread the treated cotton all around the island.

The scientists wonder if the same method might be useful in helping other protected species solve their parasite problems. Other birds may benefit, but they’re also interested in the still-declining black-tailed prairie dog: Though spraying their burrows would be labor-intensive, spraying the vegetation they often drag below ground might have the same results.

“There are other species of birds that are hurt by parasites, and so if the birds can be encouraged to incorporate fumigated cotton into their nests, then they may be able to lessen the effects of the parasites,” Knutie says. The findings were published online May 5, 2014, in the journal Current Biology.

Photo Credit: Sarah Knutie, University of Utah