Scientists studying a Caribbean island cave have unearthed something unexpected: ancient bees very much unlike the hive-dwelling insects we’re most familiar with.

For the first time ever, paleontologists have found fossil traces of burrowing bees nesting inside the buried bones of other animals. These fossils, thousands of years old, are the end result of a macabre life cycle that involved ancient rodents and giant barn owls. And they might also teach us a few lessons about bees today, the researchers say.

“I think the most important outcome is to show how diverse the nesting behavior of bees can be,” study researcher Lazaro Viñola Lopez told Gizmodo.

A “fortuitous” discovery

Viñola Lopez was working as a doctoral student for the Florida Museum of Natural History when he helped excavate the fossils from inside the cave on the island of Hispaniola (the cave is located on the eastern half of the island, owned by the Dominican Republic). But neither he nor his colleagues were planning to make such a find.

“The discovery was very fortuitous. We were looking for primates, rodents, lizards, and other vertebrates for our work on late Quaternary extinctions in the islands associated with humans and climatic changes,” he said. “We weren’t looking for any insects because they usually don’t preserve in that kind of environment.”

The cave, named Cueva de Mono, contained thousands of fossils belonging to hutia, rodents related to the guinea pig. This discovery was amazing enough, given how rare hutia fossils were to find in the area. But Viñola Lopez also noticed that one of the fossils, a specimen of hutia mandibles, had an unusual smoothness to it.

Viñola Lopez didn’t immediately dig deeper into his potential finding, and there were some bumps along the way. Based on his earlier work with dinosaur fossils, he initially speculated the hutia remains were used by wasps to build their nests, but the features of such nests didn’t quite match up with what he found.

Eventually though, he realized these remains were likely used by a different insect, an ancient species of burrowing bee, named Osnidum almontei, that lived thousands of years ago. Thanks to later trips inside the cave to recover more fossils, they also found evidence of these nests inside the vertebra of a hutia and the pulp cavity of a sloth tooth (sloths used to live in the Caribbean islands, but were largely wiped out by human activity).

The team’s findings were published Tuesday in the Proceedings of the Royal Society B Biological Sciences.

Unusual bees

Though we most commonly think of bees as social insects that build elaborate nests in plain sight, Viñola Lopez notes that most bee species are solitary and use a wide range of structures and materials for nesting. But while these ancient bees seem to share a lot in common with modern counterparts, they also stand out in important and mysterious ways.

“The bees that created these traces are similar to other bees in that they nested in the ground, but differ from all other known species in that they regularly used chambers in buried bones (such as tooth sockets),” he said. Another key distinction is the cave setting of these fossils. There’s only been one other documented instance of burrowing bees using a cave for their nests, according to the researchers, and that didn’t involve the bees using another animal’s fossil remains.

As best as they can tell, the cave was home to a population of ancient barn owls that also regularly used it as a dumping ground for the hutia they hunted. The owls might have taken the rodents back home for dinner or sometimes just pooped them out from a meal on-the-go; these remains then later proved to be an appealing site for the bees’ nesting. And while much of the surrounding area is unsuitable for these insects, the cave and others like it might have contained enough built-up soil for the bees to rely on for their nests.

Aside from learning more about bees, the team’s research has also taught them to be more cautious.

“It changed how we look at and prepare fossils from these cave deposits in the Dominican Republic. Now we take much more care before cleaning them to make sure we don’t destroy any other interesting behavior of ancient insects hiding in the sediment inside the fossils,” he said.

The ancient cave bees aren’t the only discovery the researchers are hoping to make. They’re already working to describe the many other fossils recovered from the cave, which should include never-before-characterized species of mammals, reptiles, and birds.