Inside a single fossilised tooth socket in a Dominican Republic cave, researchers found not one bee nest but six, stacked one after another across what was likely thousands of years of intermittent use. It is a nesting behaviour with no prior record anywhere in the fossil literature: bees, building inside animal bone.
The findings are described in a paper titled “Trace fossils within mammal remains reveal novel bee nesting behaviour”, published on 17 December 2025 in Royal Society Open Science. The lead author is Lazaro W. Viñola López, a postdoctoral researcher at the Field Museum in Chicago. The paper’s authors describe the discovery as the first known instance of bees using bone cavities as nesting sites, a claim that has held up across the subsequent reporting on the study rather than being softened or qualified by outside palaeontologists.
How bone ended up as a bee nursery
The bones in question did not start out as a nesting opportunity. They are the remains of hutias, a family of guinea-pig-like rodents that were common across the Caribbean, along with a smaller number of bones from an extinct sloth species. According to the paper’s account, the bones were originally deposited in the cave as prey remains, most likely dropped by owls, and accumulated in cave sediment over time. Once a tooth fell out of a jawbone, or was never replaced after the animal’s death, the socket left behind was a small, self contained cavity with a hard, protective wall already built in, which is more than a solitary bee usually gets for free.
The nests themselves date to around 20,000 years ago, based on the age of the surrounding sediment layers. Researchers identified them using CT scanning, which let them examine the internal structure of the fossils without physically breaking them open. The nest walls are a smooth, cup shaped lining, the product of a waterproof secretion solitary bees apply before laying an egg and provisioning it with food. The formal trace fossil name given to this nest architecture is Osnidum almontei, a designation for the structure itself rather than for a bee species, since no bee remains were preserved alongside the nests.
What the six stacked nests actually show
The site’s tooth sockets did not all contain a single nest. In several specimens, researchers found multiple nests layered inside one socket, with the most extreme example holding six. The team found this pattern across three of the site’s five distinct sediment layers, indicating the behaviour was not a one off but recurred at the site over what was likely an extended span of time, generation after generation of bees returning to reuse the same protected cavity once each previous occupant had emerged or died.
Viñola López described the discovery in terms that avoided treating it as more settled than it is: “This discovery shows how weird bees can be—they can surprise you. But it also shows that when you’re looking at fossils, you have to be very careful,”
a line quoted in the Field Museum’s own account of the research. That second half of the quote is doing real work. The nests were not found by anyone looking for bee behaviour. They turned up inside fossils that were being examined for entirely different reasons, as part of a broader survey of the cave’s mammal, bird, and reptile remains.
Why this had not been documented before
Solitary bees are known to nest in a wide range of pre-existing cavities: hollow plant stems, abandoned snail shells, cracks in rock, holes left by wood boring insects. Bone is a less obvious substrate, but not an implausible one once a tooth socket is empty and protected inside sediment. The absence of prior documentation is more plausibly a matter of what researchers have been looking for than a sign that the behaviour itself is new. Bee nests inside bone leave a subtle trace, easy to miss unless someone is scanning fossils with that specific possibility in mind, and there is no obvious reason to expect this cave’s bees behaved differently from bees anywhere else with access to bone.
That caution cuts against reading this as evidence of some novel evolutionary adaptation. What the paper documents is a previously uncatalogued nesting substrate in the trace fossil record — evidence of where bees nested, which says nothing about when that nesting behaviour evolved.
The distinction matters for how the finding should be used: it expands what palaeontologists know to look for in old museum collections and future excavations, more than it tells us anything new about bee biology itself.
What else the cave preserved
The Dominican Republic site is, on its own terms, a substantial fossil deposit. Reporting on the research describes tens of thousands of fossils recovered from the cave system, including rare rodent species, sloth remains, and bird, mammal, and reptile material the paper’s authors say will be formally described in future publications, alongside the more mundane rodent and reptile material that makes up the bulk of most cave deposits. The bee nests are a small part of that total picture, and the paper’s authors have been explicit that they were not what the excavation set out to find.
Some of the nest chambers preserved traces of pollen and fungal spores. The paper uses these to reconstruct the bees’ immediate nesting environment: fungal palynomorphs from the genera Canalisporium and Acrodictys point to a damp, wood-decay-rich setting, and the absence of anaerobic indicators suggests the nests formed in oxygenated sediment. Pollen made up less than one percent of the material recovered, which the researchers interpret as a sign that the larvae had already eaten their provisions before leaving the nest.
What else might be sitting in a drawer somewhere
Natural history museums hold fossil collections that were catalogued for one purpose decades ago and have not been looked at closely since. Bee nests inside bone leave a specific, recognisable trace once someone knows to look for it, which means the more interesting test of this finding may not require a new excavation at all. It may just require someone reopening a drawer of bones filed under a different animal entirely, and checking the empty sockets as carefully as the teeth themselves.
