Ancient Bees Found Nested Inside Fossilized Bone — A Behavior Never Seen Before

When paleontologists examined fossils from a cave in Hispaniola, they discovered much more than the remains of extinct animals. The bones also preserved evidence of unusual behavior: insects nesting inside fossils.

This behavior left behind the first known evidence of bees nesting in pre-existing fossil cavities, according to a new study in Proceedings of the Royal Society B reports. The discovery shows how environmental pressures shaped insect behavior and how these adaptations were preserved alongside the fossils themselves.

Giant barn owls and the creation of fossil archives

The fossils come from a limestone cave in the southern Dominican Republic known as Cueva de Mono. Evidence from the site suggests that it served for many generations as a nesting and feeding ground for giant barn owls, which carried prey into the cave to feed their chicks.

Among the remains are thousands of bones of hutias, large Caribbean rodents that are otherwise rare in the island’s fossil record. Outside the cave, hutia fossils appear only occasionally, often as isolated teeth or jaw fragments. Inside the cave, they are abundant.

By repeatedly hunting in the same areas and returning to the same roost, the owls gradually concentrated the remains of their prey inside the cave. Some animals were probably brought in whole, while others were eaten elsewhere and then regurgitated as compact pellets.

As bees later tunneled through fine, clay-rich sediments, some encountered fossilized remains. Instead of abandoning these sites, the insects appear to have used the hollow spaces in the bones – including empty tooth sockets – as ready-made nesting chambers.

Learn more: Bumblebees and ants fight in violent nectar wars, leading to death and food shortages

How burrowing bees turned fossils into nests

Burrowing bees typically dig narrow tunnels in exposed soil that lead to small underground chambers where eggs develop. Nesting inside caves is rare and the use of pre-existing fossil cavities as nesting sites has never been documented.

Researchers identified smooth-lined cavities inside the jaws and vertebrae of hutia recovered from the cave, as well as in the pulp cavity of a sloth tooth. The interiors lacked the rough texture of bone and instead showed signs of deliberate coating.

Many burrowing bees cover the inside of their nest with a waxy secretion produced by specialized glands. The coating waterproofs the chamber and leaves a smooth interior surface, a characteristic that distinguishes honeycombs from those made by wasps or other insects.

CT scans showed that some cavities had been reused multiple times. In a hutia jaw, a single tooth socket contained six stacked nesting chambers, each placed inside the previous one. This pattern suggests that bees returned to existing cavities rather than digging new tunnels once the first occupants emerged.

There is no evidence that insects drilled into or remodeled the fossils. Instead, they used hollow spaces that already existed and closely matched the size and geometry of their nests. What remains is not the bees themselves, but physical traces of their behavior – an ichnofossil preserved in the remains of much larger animals.

Why environmental pressure has changed bee nesting behavior

Environmental constraints likely shaped the bees’ unusual nesting behavior. Much of Hispaniola is dominated by sharp limestone karst, which contains little of the fine, stable soil that burrowing bees typically need to build their nests.

The caves offered a rare alternative. Sediments accumulated in sheltered pockets and fossilized bones and teeth made up protected cavities that closely matched the size and shape of the bees’ nesting chambers.

The evidence points to a sequence driven by availability rather than preference. Predators concentrated the animal remains in the cave, sediment accumulated around them, and, much later, insects exploited both the soil and the hollow spaces preserved in the fossils.

Learn more: Leeches didn’t always suck blood – ancient fossils reveal they swallowed their prey whole

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