Researchers have discovered six ancient bee nests stacked inside a single 20,000-year-old animal tooth socket in a Dominican Republic cave. Published on 17 December 2025 in Royal Society Open Science, the finding marks the first documented instance in paleontological history of solitary bees using fossilized bone cavities as nurseries.
Cueva de Mono and the Accidental Fossil Nursery
The unusual nesting site was uncovered in a limestone sinkhole cave known as Cueva de Mono in the southern Dominican Republic. The cave served for generations as a long-term roost for giant barn owls that repeatedly brought prey back to feed their young. According to reporting from Sciencedaily, owls swallow prey whole and later regurgitate indigestible remains as tightly bound pellets, creating deep deposits of small mammal bones on the floor over centuries.
Among those accumulated remains were the bones of hutias, a family of guinea-pig-like rodents once common across the Caribbean, alongside a smaller number of bones from an extinct sloth species. Over time, those floor deposits slowly turned to stone, preserving remnants from more than fifty species. When an animal’s tooth eventually fell out of a jawbone or was lost after death, it left behind a hollow space known as an alveolus. These empty tooth sockets provided solitary bees with a ready-made, protected cavity featuring a hard structural wall.
Uncovering Osnidum almontei Through Careful Excavation
The discovery emerged from meticulous examination rather than a targeted search for insect behavior. While cleaning and excavating fossil material as a doctoral student at the Florida Museum of Natural History, Lázaro Viñola López noticed that sediment inside the jaw sockets did not match normal random buildup.
Instead of rough soil, the interior surfaces of the sockets were smooth and concave. Recalling similar experiences collecting dinosaur fossils in Montana in 2014, the researcher initially suspected wasp cocoons. Further investigation alongside colleague Mitchell Riegler revealed that the structures lacked the rough walls made of chewed plant material and saliva typical of wasps. Instead, microscopic and structural analysis showed smooth, cup-shaped linings formed by a waxy, waterproof secretion deployed by solitary bees.
Because soft-bodied insects do not preserve well over millennia in humid cave environments, no actual bee remains survived. However, the distinct architecture of the nests allowed scientists to classify them as a new ichnofossil—a trace fossil recording past animal behavior rather than body parts. Researchers named the trace fossil Osnidum almontei, honoring Juan Almonte Milan, the Dominican paleontologist who initially identified the cave as scientifically significant.
Stacked Nests Across Sediment Layers and Evolutionary Implications
Advanced CT scanning enabled the research team to examine the internal structure of the fossils without physically breaking them open. In several specimens across three of the site’s five distinct sediment layers, researchers found multiple nests layered sequentially inside a single tooth socket, with the most extreme example holding six stacked nests. This recurring pattern indicates that generations of bees returned to the same protected cavity after previous occupants emerged or died.
While more than 90 percent of bee species live solitary lives and typically dig nests straight into open soil, none had ever been documented repurposing bone cavities. Beyond hutia jaws, researchers also identified a nest inside the pulp cavity of an extinct tree sloth tooth and another within the spinal cord space of a hutia vertebra.
The study highlights a hidden layer of taphonomy and fossil preservation. Because limestone caves are widespread across Hispaniola and museum collections contain countless fossilized jaws gathered for mammalian research, similar bee nests may already be sitting unnoticed in archives worldwide, awaiting closer inspection by researchers scanning for trace fossil architecture.