Megachile bees, or leaf cutting bees, are solitary creatures with distinct nesting habits. In contrast to honey bees, which congregate in large hives with queens and workers, members of the megachile family nest alone in small, natural cavities that they line with leaves and petals. But in the fields of Argentina, a team of researchers recently stumbled upon something strange: a megachile nest made entirely of plastic.

Between 2017 and 2018, the researchers set up 63 trap nests on farmland in San Juan. The trap nests, according to Michelle Starr of Science Alert, consisted of long, hollow tubes—similar to the bee hotels that you can buy to entice solitary bee species to your backyard. The scientists checked on the nests monthly to track any building progress, and ultimately recorded just three nests. Two belonged to the species Megachile jenseni Friese; the nests’ brood cells, where the eggs are laid, were made from petals and mud. The cells of the other nest were constructed exclusively from plastic, the team writes in the journal Apidologie.

This unusual nest consisted of three cells, made up of plastic pieces that had been cut into oblong and circular shapes—just as megachile bees typically do with leaves. The first two cells were constructed from a light blue plastic that seemed to come from a shopping bag. The third cell was made from a thicker, white plastic. One cell contained a dead larva, one was left unfinished, and one appeared to have housed a larva that grew to adulthood and left the nest.

The researchers aren’t entirely sure which type of bee built the plastic abode, but they suspect it was Megachile rotundata, a species that had been seen at the study site and has been previously known to use plastic into while constructing its brood cells. Indeed, a 2013 study found that M. rotundata bees in Toronto incorporated cut pieces of plastic bags into their nests, while the species Megachile campanulae, which builds its nests out of plant and tree resins, made brood cells out of building sealant. But the researchers behind the new report say they have documented the first known instance of plastic being used to build an entire bees' nest.

What this means for the buzzing critters is not clear. On the one hand, it suggests that at a time when bees around the world are experiencing a worrying decline, some species are managing to adapt to a changing environment. “The replacement of natural materials by plastic could appear in response to a limitation in the availability of vegetation in the fields, which could be directly linked to the use of herbicides,” the study authors write. Synthetic materials may even confer some advantages over natural ones; sparrows and finches, for instance, have been known to stuff cigarette butts into the lining of their nests as a means of warding off parasitic mites.

But like cigarette butts, plastic pieces could also be causing harm to the animals that use them. There is no evidence that bees are eating the synthetic materials built into their nests, but microplastics—tiny fragments that break off from larger pieces—are known to threaten a wide array of marine animals, even those that don’t ingest the plastics directly. Hollis Woodard, an entomologist at the University of California Riversides Woodard Lab, tells Sarah Gibbens of National Geographic that more research is needed to uncover the impact of bees’ plastic use. But she suspects the effects are not entirely beneficial.

“I think it’s really sad,” Woodard says. “It’s another example of the rampant use of materials that end up in places we don’t intend them to.”