Contrary to the popular idea of bee nests as large, elaborate hives hanging from trees, most bee species are about 90% – are actually solitary and build their nests in the ground or among rotting logs and plant stems.
But researchers recently discovered perhaps one of the most unusual nesting sites yet: Inside a limestone cave on the Caribbean island of Hispaniola, a trove of fossilized bones, some of which belonged to now-extinct animals, was found and was home to tiny ancient bee nests built in empty tooth sockets. According to scientists, this is the first time that bees have used bones for nesting and laying eggs. for research published Tuesday in the journal Royal Society Open Science.
“It was very surprising because you'll never find invertebrates there—you'll find snails, but you won't find insects,” said lead author Lazaro Viñola-Lopez, a postdoctoral fellow at the Field Museum of Natural History in Chicago. “Usually in this cave you find rodents, birds and all this fauna. So finding evidence of ancient bees in these cave deposits was very interesting. This is the first time we've encountered this in the Caribbean.”
The findings help fill a gap in the fossil record, since all other bee fossils described in the Caribbean were found in amber and are about 20 million years old, Vignola-Lopez explained.
The hoard of fossilized bones was home to tiny ancient bee nests built in empty tooth sockets. – Courtesy of Lazaro Viñola Lopez
The study authors believe the fossils containing bee nests date back to about 20,000 years ago and could shed light on how bees adapted to their environments even in the ancient past.
“Very little is known about the ecology of many bees on these islands,” Vignola-Lopez said. “This shows that the diversity of bee nesting processes is actually very large and sometimes goes beyond what we consider normal… It also suggests that we need, when we prepare samples, to look carefully for anything that might be preserved within them that might be exhibiting very strange behavior from species that we think we understand relatively well.”
A fossil within a fossil
Paleontologist Juan Almonte Milan first discovered the cave on the island of Hispaniola. – Courtesy of Lazaro Viñola-Lopez
In the summer of 2022, Viñola-Lopez explored the cave with colleagues in search of specimens to study for his doctoral program at the University of Florida and the Florida Museum of Natural History. The cave itself has its own history, as it contains layer upon layer of fossils of more than 50 species, including rodents, birds and reptiles.
The study authors believe that a family of barn owls once lived in the cave and coughed up the bones of their prey, which eventually became fossilized. The owls may have remained in the cave for generations, leading to the accumulation of thousands of fossils. Other species, such as turtles and crocodiles, may have fallen into the cave, which has a drop of about 8 meters at the entrance, and ultimately died when they were unable to climb back out. The environment, protected from external weather, facilitated further preservation of the specimens.
But when Vignola-Lopez took a closer look at the fossils, he noticed something strange: the dirt lining the inside of tooth sockets reminded him of how wasps can build their cocoons.
The research team collected fossils from different vertebrate species. – Courtesy of Lazaro Viñola-Lopez
After performing CT scans and X-ray technology, which creates detailed 3D images, the authors were able to determine that the small nests were made of dirt and belonged to bees. Wasp nests are made from a mixture of saliva and chewed plant fibers, but the nests from the cave were smooth on the inside, indicating a bee nest-building process that uses compacted mud and a secreted waxy substance that coats the inside of the walls.
“This is a very interesting record because bees generally like shaded areas sometimes, some of them can be nocturnal, but nesting in a cave is a very, very strange behavior,” Vignola-Lopez said. According to the Florida Museum of Natural History, there is only one recorded case of a burrowing bee nesting inside a cave. “We also know that more than one specimen did this. Even in one hole in the lower jaw, up to six generations of bees return to the same hole… So it looks like it was probably a large communal nest.”
However, although the steamy cave preserved fossils, the conditions were not ideal for preserving insect bodies. Therefore, the authors were unable to determine what type of bees nested in the cave. It is also unclear whether the nests were built by an extinct species of bee or one that still exists today. So far, their nests are the only named specimens, now known as Osnidum almontei, after Juan Almonte Milan, the scientist who first discovered the cave, according to the study.
“This is remarkable work presented by these researchers and adds to the knowledge of 'hidden biodiversity'. This means that although no fossils of bee bodies were found in the cave, their trace fossils (ichnofossils) allow the diagnosis of soil bees. These bee cells tell us about the environment and ecosystem they lived in,” said Stephen Hasiotis, a geology professor at the University of Kansas at Lawrence whose research focuses on paleontology and ichnology, or the study of trace fossils. Chasiotis was not involved in the new study.
“The bees likely built their nests in the cave soil because the humidity inside the cave and soil was almost constant,” he added in an email. “The area was likely protected from heavy rainfall and flooding, not to mention protected from the many potential predators and omnivores of various sizes living in the soil in which they were hidden.”
Viñola-Lopez said he hopes to return to the area to conduct further research that may help determine whether the bees are still in the area and whether this behavior is observed in other caves and on other islands.
The bees' nests were classified as Osnidum almontei, named after Juan Almonte Milan. – Courtesy of Lazaro Viñola-Lopez
“This discovery is doubly surprising because modern bees are not known to use bones for their nests, and they don't nest in caves. But these fossil bees, incubating chambers in sediment-filled parts of bones, tell us that their creators could have done both, and that's interesting to know,” said Anthony Martin, a professor of environmental science in the department of environmental sciences at Emory University in Atlanta. Martin is the author of the 2023 book Sculpted Life: Tales of the Animals, Plants, and Fungi That Drill, Break, and Scrape to Shape the Earth.
“Insects have been adapting to environmental changes for nearly 400 million years, and ground-dwelling bees have been around for about the last 100 million years of that time,” said Martin, who was not involved in the new study. “So this exciting discovery of fossils of bees nesting in bone cavities and caves serves as a good reminder that when it comes to evolution, bees will continue to be the bees they are meant to be.”
Taylor Nicoli is a freelance journalist based in New York.
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