Contrary to popular depictions of bee nests as large, intricate hives hanging from trees, the majority of bee species – around 90% – are actually solitary, building their nests in the ground or in rotting logs and plant stems.
But researchers recently discovered what is perhaps one of the strangest nesting sites: Inside a limestone cave on the Caribbean island of Hispaniola, a trove of fossilized bones – some from now-extinct animals – housed tiny, ancient bee nests built into empty tooth sockets. This is the first time bees have been recorded using bones for nesting and laying eggs, according to a study published Tuesday in the journal Royal Society Open Science.
“It was very surprising, because you never find invertebrates there — you find snails there, but no insects,” said lead author Lázaro Viñola-López, a postdoctoral researcher at the Field Museum of Natural History in Chicago. “Usually what you find in this cave is rodents, birds, like all this wildlife. So finding evidence of ancient bees in these cave deposits was very exciting. The first time we’ve had this in the Caribbean.”
These findings help fill a gap in the fossil record since all other bee fossils described in the Caribbean were found in amber and are much older, dating back about 20 million years, Viñola-López said.
A trove of fossilized bones housed tiny ancient honeycombs built in empty tooth sockets. – Courtesy of Lazaro Viñola López
The study authors believe that fossils housing bee nests date back about 20,000 years 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,” Viñola-López said. “This shows that the diversity of bee nesting processes is actually very great and sometimes extends beyond what we think is normal. … It also indicates that we need, when we prepare specimens, to look more closely at anything that may be preserved inside them, which may show very strange behaviors of 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 Lázaro Viñola-López
Viñola-López was exploring the cave with colleagues in the summer of 2022, looking for specimens to study for her doctoral program at the University of Florida and the Florida Museum of Natural History. The cave itself holds 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 spat out the bones of their prey, which eventually 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, could have fallen into the cave – which has a drop of around 8 meters at the entrance – and ended up dying because they could not get out. The environment, protected from bad weather, made it possible to better preserve the specimens.
But when Viñola-López examined the fossils more closely, he noticed something strange: The dirt covering the inside of the tooth sockets reminded him of the way wasps might build their cocoons.
The research team collected fossils of different vertebrate species. – Courtesy of Lázaro Viñola-López
After performing CT scans, an X-ray technology that creates detailed 3D imaging, the authors were able to determine that the small nests were made of mud and belonged to a bee. While wasp nests are made of a mixture of saliva and chewed plant fibers, the cave nests were smooth on the inside, indicating the process of building a bee’s nest, which uses compacted earth and a secreted waxy substance that lines the inside of the walls.
“It’s a very interesting recording because generally for bees, sometimes they like shady areas, some of them can be nocturnal, but nesting in a cave is a very, very strange behavior,” Viñola-López said. There is only one other recorded case of a burrowing bee nesting in a cave, according to a release from the Florida Museum of Natural History. “We also know that it’s not a single specimen that did this. Even in a single hole in a mandible, there are up to six generations of bees coming back to that same hole. … So it seems like this was probably a large communal nest.”
However, even though the damp cave preserved fossils, the conditions were not ideal for preserving insect bodies. The authors were therefore unable to determine which species of bee nested in the cave. It is also unclear whether the nests were built by an extinct species of bee or by one still present today. For now, their nests are the only named specimen, now known as Osnidum almontei, in homage to Juan Almonte Milan, the scientist who first discovered the cave, according to the study.
“This is great work presented by these researchers which adds to the file of “hidden biodiversity”. This means that even though no bee body fossils have been recovered from the cave, their trace fossils (aka ichnofossils) are diagnostic of soil bees. These bee cells tell us about the environment and ecosystem in which they lived,” said Stephen Hasiotis, a geology professor at the University of Kansas in Lawrence, whose research focuses on paleontology and ichnology, or the study of trace fossils. Hasiotis was not involved in the new study.
“The bees probably built their nests in the floor of the caves, as the humidity in the cave and in the ground would have been almost constant,” he added in an email. “The area was likely protected from heavy rains and flooding, not to mention it was also protected from many potential predators and omnivores of various sizes co-inhabiting the soils in which they burrowed. »
Viñola-López said he hopes to return to the area to conduct further surveys that could help determine whether the bees are still in the area — and whether this behavior is found in other caves and on other islands.
The honeycombs were classified as Osnidum almontei, named after Juan Almonte Milan. – Courtesy of Lázaro Viñola-López
“This discovery is doubly surprising, because modern bees are not known to use bones for nesting, nor are they known to nest in caves. But these fossil bees brooding chambers in sediment-filled parts of bones tell us that their creators could do both, which is exciting to know,” said Anthony Martin, professor of practice in the department of environmental sciences at Emory University in Atlanta. Martin is the author of the 2023 book, “Life Sculpted: Tales of the Animals, Plants, and Fungi that Drill, Break, and Scrape to Shape Earth.”
“Insects have been adapting to changes in their environment for almost 400 million years, and ground-nesting bees have been around for about 100 million years,” said Martin, who was not involved in the new study. “This exciting discovery of bee fossils nesting in bone cavities and caves reminds us that when it comes to evolution, bees will continue to be the bees they need to be.”
Taylor Nicioli is a freelance journalist based in New York.
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