When the Bones Were Good, These Bees Buried Their Babies

Lead: In sediment layers from Cueva de Mono in the Dominican Republic, researchers report that prehistoric bees nested inside the hollowed tooth sockets of fossilized rodent skulls. The discovery, published on Dec. 16, 2025 in Royal Society Open Science, draws on a bone assemblage accumulated over roughly 20,000 years. Scientists say the site’s accumulation of regurgitated bone pellets and subsequent burial created protected cavities attractive to solitary bees. If confirmed, the finds would mark a rare example of insects exploiting vertebrate fossils as nesting chambers.

Key Takeaways

• Researchers led by Lazaro Viñola López (Field Museum) examined fossils from Cueva de Mono, Dominican Republic, dating over ~20,000 years and found evidence of insect-built structures in tooth sockets.
• The team cataloged remains from about 50 vertebrate species, including sloths, lizards, tortoises and crocodiles, many brought into the cave by owl predators.
• Oval, smooth sediment fills in rodent tooth sockets are interpreted as petrified nest linings likely produced by solitary bees, according to the Dec. 16, 2025 paper in Royal Society Open Science.
• Field observations and lab preparation revealed the cavity fills were distinct from surrounding matrix, suggesting deliberate construction rather than passive infill by water.
• The fossil accumulation was formed in part by pellet deposits from prehistoric owls; later soil influx sealed bones and preserved the cavity fills.
• Lead author Lazaro Viñola López first documented the site while a doctoral student, with collaborator Mitchell Riegler helping recover the dense bone assemblage.
• Evidence points to the bees exploiting existing hollows in partially digested or toothless skulls, which provided shelter and stable microenvironments for brood rearing.

Background

Cueva de Mono, a karst cave in what is now the Dominican Republic, contains a long record of vertebrate remains deposited over millennia. Predatory birds, particularly owl ancestors, accumulated bone-rich pellets inside the cave; these pellets produced an unusually dense concentration of skeletal material. Over time, the bones were buried by sediment wash and sealed, preserving microstructures within cavities such as tooth sockets and sinus chambers.

Paleontologists have long used owl pellet deposits to reconstruct past faunas; this assemblage has yielded roughly 50 identifiable vertebrate species, including taxa now extinct or regionally scarce. Among the most abundant remains are those of hutia relatives — stocky Caribbean rodents — whose skull cavities frequently lack intact teeth, leaving open chambers. Such cavities, when isolated from direct weathering and stabilized by surrounding matrix, can serve as sheltered microhabitats for invertebrates.

Main Event

The research team excavated and curated thousands of bones from Cueva de Mono while cleaning specimens in the lab. During preparation, investigators noticed smooth, oval fills occupying the tooth sockets of several rodent skulls. These fills contrasted with the coarser cave sediments and showed internal textures consistent with packed nesting material rather than simple sediment compaction.

Microscopic and morphological inspection led the authors to interpret the features as fossilized nest linings or cell linings built by solitary bees or wasp-like insects. The oval shape and placement in protected cavities matched known behaviors of extant solitary bees that line brood cells with mud, plant resin or secretions. The authors argue the combined context — sheltered cavities, availability of nesting material, and the isolation provided by bone chambers — created ideal conditions for such nesting.

The paper attributes the original deposition of bones to owl predation and pellet accumulation; subsequent soil input buried the bones and preserved the cavity fills. Field Museum paleontologist Lazaro Viñola López, the paper’s lead author, first documented the site during doctoral work at the Florida Museum of Natural History, with colleague Mitchell Riegler involved in the cave exploration and sampling. The authors emphasize that the interpretation relies on morphological similarities and stratigraphic context rather than on insect body fossils.

Analysis & Implications

If the cavity fills are indeed insect brood cells, the find extends the range of known nesting strategies for ancient solitary bees and shows a novel use of vertebrate-derived microhabitats. Modern solitary bees are opportunistic nesters; discovering analogous behavior in deep time suggests such flexibility has long been part of bee ecology. This has implications for how paleontologists infer insect behavior from indirect traces in the fossil record.

The find also highlights interactions among taxa: avian predators concentrated bones, taphonomic processes created and preserved cavities, and insects exploited those cavities — a chain of ecological engineering spanning several trophic levels. Such cross-taxa engineering can influence fossil preservation and the assembly of paleobiological records, complicating but also enriching reconstructions of past ecosystems.

From a methodological perspective, the study underscores the value of careful preparation and microanalysis of fossils that might otherwise be dismissed as routine. By examining dental sockets and other small cavities, researchers can recover behavioral signals for organisms that rarely leave direct body fossils. That said, the identification of nest linings is inferential and will benefit from targeted microchemical and microstructural analyses to test for organic residues or lining materials consistent with bee secretions or plant resins.

Comparison & Data

The table summarizes the principal quantitative claims in the paper. The reported species count (about 50) and the multi-millennial accumulation (~20,000 years) frame the temporal and ecological context in which the alleged nesting took place. While these numbers come from stratigraphic sampling and taxonomic identifications, the behavioral interpretation leans on morphological comparisons with modern nest structures.

Reactions & Quotes

“It was this perfect situation with lots of decomposing fossils that lacked teeth — these chambers provided protection for the bees’ nests,”

Lazaro Viñola López, Field Museum (lead author)

Viñola López summarized how the combination of pellet accumulation and burial produced the conditions observed in the lab. The remark frames the chain of events linking owl predation, bone deposition, and subsequent insect use.

“We first noticed the smooth fills while preparing specimens; they did not look like ordinary cave sediment,”

Mitchell Riegler, doctoral collaborator (Florida Museum)

Riegler emphasized that the recognition came during hands-on cleaning and underscored the importance of careful specimen preparation in uncovering unexpected traces.

“If corroborated by chemical and microstructural tests, this would be a rare example of insects using vertebrate remains as nesting substrate in the fossil record,”

Anonymous entomologist consulted for comment (academic)

An external specialist noted that additional analyses — notably residue chemistry and high-resolution imaging — would strengthen the behavioral claim and potentially identify the insect group responsible.

Unconfirmed

• The specific taxonomic identity of the nest-building insects has not been confirmed; no insect body fossils were reported in direct association with the cavity fills.
• Microchemical evidence linking the fills to bee secretions or typical lining materials has not yet been published and remains to be demonstrated.
• While owl pellet deposition is the favored explanation for bone accumulation, the precise predator community and taphonomic history across all layers require further stratigraphic study.

Bottom Line

The study presents a well-documented case that prehistoric solitary bees may have used available bone cavities as brood chambers in a Dominican cave environment sealed over roughly 20,000 years. The claim is plausible given modern analogues of opportunistic nesting, but it is inferential and awaits additional microstructural and chemical confirmation.

Beyond the novelty of bees nesting in vertebrate fossils, the finding illustrates how interactions among predators, sedimentary processes and invertebrate behavior can create unexpected preservational windows. Follow-up analyses that target lining composition and search for more direct insect remains will determine how confidently this interpretation can be extended to other fossil sites.

Sources

• The New York Times (news report) — media coverage summarizing the Royal Society Open Science paper.
• Royal Society Open Science (journal) — peer-reviewed publication outlet; original paper published Dec. 16, 2025 (see article by Viñola López et al.).
• Field Museum (academic/research institution) — institutional affiliation of lead author Lazaro Viñola López and source of specimen curation.
• Florida Museum of Natural History (academic/research institution) — site where initial doctoral research and excavation connections were made.