Scientists studying a cave on a Caribbean island have unearthed something unexpected: ancient bees are very different from the house-dwelling insects we are most familiar with.

For the first time, paleontologists have found fossilized tracks of burrowing bees nesting inside the buried bones of other animals. These fossils, thousands of years old, are the end result of a terrifying life cycle involving ancient rodents and giant barn owls. And they can also teach us some lessons about today’s bees, the researchers say.

“I think the most important result is showing how diverse bees’ behavior is,” study researcher Lazaro Viñola Lopez told Gizmodo.

A “fateful” discovery

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

“The discovery is very exciting. We are looking for primates, rodents, lizards, and other vertebrates for our work on late Quaternary extinctions on islands associated with humans and climate changes,” he said. “We didn’t look for any insects because they usually don’t survive in that kind of environment.”

The cave, named Cueva de Mono, contains thousands of fossils belonging to hutia, rodents related to guinea pigs. This is a very unusual discovery, due to the unique hutia fossils found in the area. But Viñola Lopez also noticed that one of the fossils, a specimen of hutia mandibles, had a remarkable smoothness to it.

Viñola Lopez did not immediately analyze his potential search, and there were some bumps in the road. Based on his previous work on dinosaur fossils, he first speculated that the hutia remains were used by wasps to build their nests, but the parts of those nests didn’t quite match what he found.

But eventually, he realized that these remains were probably used by another insect, an ancient species of burrowing bee, named. Osnidum almontei, who 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 hutia’s vertebrae and the dull tooth cavity of the sloth (sloths used to live on the Caribbean islands, but this mostly erased by human activity).

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

Amazing bees

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

“The bees that create these signs are similar to other bees in that they nest on the ground, but differ from all known species in that they often use chambers of buried bones (like teeth),” he said. Another important difference is the cave placement of these fossils. There is only one other documented example of bees using a cave for their nests, according to the researchers, and that doesn’t involve bees using the fossil remains of another animal.

As far as they know, the cave is home to a population of ancient barn owls who also often use it as a den for the hutia they hunt. The owls may have brought the mice home for dinner or sometimes just thrown them out of the meal on-the-go; these remains then later proved to be an attractive place for bees to nest. And while most of the surrounding area is unsuitable for these insects, the cave and others like it may have enough built-up land for the bees to build their nests.

Besides learning more about bees, the group’s research also taught them to be more careful.

“This has changed how we see and prepare the fossils from these cave deposits in the Dominican Republic. Now we are very careful before cleaning them to make sure we don’t destroy any other interesting behavior of the ancient insects hiding in the sediment inside the fossils,” he said.

Ancient cave bees aren’t the only discovery researchers hope to make. They are already working to describe the many other fossils recovered from the cave, which should include undescribed species of mammals, reptiles, and birds.