A giant barn owl, a type of rodent called a hutia, and a burrowing bee entered the cave. Only two people remained. Which one is left? The answer is impossible.
This unusual series of events likely occurred on the Caribbean island of Hispaniola thousands of years ago. The owl brought Huthia back to the cave to feed the chicks. The meal was quickly over, and the bodies of the unfortunate rodents littered the cave floor. Much later, bees came looking for a place to nest in the rubble left behind.
How did bees turn into fossils and become nests?
The bees began digging through the fine clay-rich silt that had accumulated in the dark parts of the cave. Before reaching the required depth, we encountered the remains of Khthia.
This was helpful. Phthia’s teeth were once held in small holes in the jaw known as alveoli. Although the teeth themselves were gone, these cavities remained intact and empty. Its size roughly corresponded to what bees need for their hives.
Over time, more bees took advantage of the natural cavities inside the fossilized bones as ready-made nest sites. Long after owls, hutia, and perhaps even bees disappeared, paleontologists discovered this unusual record preserved in stone.
Careful observation leads to discovery
Without careful attention during excavation, the discovery might have been missed.
“Normally, when we collect fossils, we remove all the sediment from the alveoli while cleaning the specimen,” said Lázaro Vignola López, who excavated the fossil while working as a doctoral student at the Florida Museum of Natural History.
Vignola López was particularly interested in this type of hutia, which is rarely found elsewhere on the island. At Cueva de Mono in the southern Dominican Republic, he discovered thousands of fossils that appeared to be of the same species. The cave may have served as a long-term feeding ground for giant barn owls, which repeatedly brought prey back to the same location over generations.
Rather than cleaning the fossils right away, he examined them closely. One cavity stood out. The reason was that its inner surface was smooth, not rough like bone.
Wrong identity: wasp or bee?
“I had seen something similar in Montana when I was collecting dinosaur fossils in 2014,” he said. At the time, he and his colleagues discovered wasp cocoons mixed in with the fossil material. He initially thought the same explanation applied here. He remembers thinking, “It would be nice to write a short paper reporting this wasp nest in the mandible.”
He shared the idea with colleague Mitchell Riegler, another doctoral student at the museum. Mr. Riegler was not immediately convinced. “I thought, Lazarus, it’s a niche project, there’s so much else to do.”
The idea was put on hold until Riegler was challenged by a former advisor to write a scientific paper within a week.
“He and I played a game back and forth where we had to write a paper in a week.”
Initially, the research team believed they were recording a wasp nest. But after studying fossil fish, which are traces of past activity such as footprints, droppings, and nests, they realized something didn’t add up.
Wasp nests usually have rough walls made of chewed plant material and saliva. The structure of the fossil was smooth. However, bees often coat their nests with a waxy secretion, creating a waterproof polished interior. This detail revealed the identity of the nest builder.
They were studying honey bees, not wasps.
rare and unprecedented action
This modification makes this finding even more significant. There is only one other known case of burrowing bees building a nest in a cave, and there is no example of bees using existing fossil structures without modification. Previous reports have described bees boring into human bones, but they don’t simply occupy these natural cavities.
Recognizing the importance of their discovery, the researchers slowed down and expanded their research. They consulted modern bee experts and reviewed the scientific literature in detail. Vignola López returned to the cave to examine the geological formations.
At some point, the cave faced a potential threat when someone tried to develop the land and turn the cave into a septic tank. Although the project was ultimately abandoned, the team moved quickly to recover as many fossils as possible.
“We had to participate in the rescue operation and extract as many fossils as possible, and we were able to get a lot of fossils,” Vignola López said.
Nest found with multiple types of fossils
The final study looked in detail at the history of the cave and the unusual nesting behavior of these bees. The nest was not limited to Futiajo.
In one case, a nest was discovered within the pulp cavity of a sloth tooth. Sloths once lived in the Caribbean, but they disappeared after humans arrived. Another nest was discovered inside Phthia’s vertebrae, in the space that once housed the spinal cord.
A CT scan revealed the presence of multiple layers of nests in some cavities. Rather than digging new tunnels, certain bees reused existing tunnels if they were empty. In one case, six nests were stacked inside one alveolus, placed one inside the other like a Russian doll.
Why bees moved to caves
This study also provides an explanation for this unusual behavior. The surrounding terrain is made up of karst, a type of sharp limestone landform with no stable soil.
“The area we were sampling from is karst, so it’s made of sharp limestone and all the natural soil has been lost,” Riegler said. “I actually fell into it once too, so I’ll tell you all about it.”
Soil that accumulates on the surface is often washed into caves, where it precipitates and forms pockets of suitable material. These deposits may have provided some of the only viable nesting conditions for burrowing bees in this area.
A cave full of stories still to be told
Researchers are continuing to study other fossils recovered from the cave, and expect more discoveries in future publications.
Their works are Proceedings of the Royal Society Breveals remarkable examples of how life can adapt in unexpected ways. In this case, the cave, filled with the remains of past meals, became a refuge for a completely different kind of inhabitants.
Important points
- Scientists studying a cave on the Caribbean island of Hispaniola have discovered the first known evidence that ancient honeybees nested in natural cavities in fossilized bones, a behavior that had never been previously recorded.
- Burrowing bees typically nest in open soil rather than in caves. There is only one other record of cave nesting. In this case, the researchers believe the bees adapted because there was little soil available outdoors, and the fine sediment inside the cave provided a suitable alternative.
- The cave itself was formed by generations of giant barn owls, which carried prey inside, leaving behind bones, eggshells, and other debris. These accumulated over time, creating a unique environment that supported both the owls and the subsequent nesting bees.
