Lead
Researchers have identified tiny mud nests built by bees inside fossilized skulls and jaw bones recovered from a limestone cave on Hispaniola, a discovery published 17 December 2025 in Royal Society Open Science. The finds, dated to roughly 20,000 years ago, represent the first recorded use of bones as nesting substrate by bees and expand the known range of bee nesting behaviours in the Caribbean. Field and museum scientists say the nests were constructed within empty tooth sockets and other cavities preserved in a multi‑species fossil deposit. The result suggests complex, repeated nesting activity — likely over multiple generations — in a protected cave environment.
Key Takeaways
- Researchers reported the nests in a study published 17 December 2025 in Royal Society Open Science; the material comes from a limestone cave on Hispaniola and was examined using CT scans and 3D X‑ray imaging.
- The bone nests are estimated to be about 20,000 years old, filling a temporal gap between older Caribbean bee fossils found in amber (circa 20 million years) and modern records.
- Up to six successive generations of brood cells were identified within a single tooth socket, suggesting repeated reuse of the same cavities.
- The nests’ internal texture and composition—compact mud lined with a waxy coating—match soil‑nesting bee construction rather than wasp paper nests.
- No bee body fossils were preserved in the cave deposits; the named trace fossil, Osnidum almontei, identifies the nesting structure, not a preserved species body.
- Investigators hypothesize barn-owl accumulation and an 8‑meter sink into the cave as factors in the mass fossil deposit that preserved the nesting traces.
- The discovery suggests that some bees used shaded, humid cave soils and bone cavities as secure nesting sites, a behaviour not previously documented in the Caribbean fossil record.
Background
Most people picture bees as social, tree‑hanging hive builders, but about 90% of bee species are solitary and nest in soils, rotten wood or plant stems. Fossil evidence for these solitary behaviors is sparse in island contexts because body fossils are rare and amber records represent much older time slices. The Hispaniola cave contains layered deposits from more than 50 vertebrate species, accumulated over generations by predators such as barn owls and by animals falling into the cave’s steep entrance.
Bone preservation in the cave—protected from storms and flood events—created an unusual archive. Over time some bone cavities became filled with sediment that later hardened and fossilized, offering an opportunity for small organisms to leave trace fossils. Trace fossils (ichnofossils) like brood cells, tunnels and borings record behaviour rather than anatomy and can reveal activities that body fossils alone do not capture. Until now, Caribbean bee trace fossils had not been reported from cave deposits.
Main Event
The discovery began during a 2022 field survey when researchers from the Field Museum and collaborators retrieved fossil bones for study. In the lab, a team led by postdoctoral researcher Lázaro Viñola‑López noticed unusual, soil‑filled cavities within jaws and tooth sockets. High‑resolution CT scanning revealed discrete, mud‑lined cells consistent with bee brood chambers rather than animal burrows or detritus.
Comparative analysis of internal morphology showed smooth, compacted walls coated with a waxy lining—characteristic of ground‑nesting bees that seal cells for larvae. The architecture differed from wasp mud nests, which incorporate chewed plant fibers and saliva and present a fibrous internal texture. Multiple stacked cells within single sockets indicated repeated reuse over time.
Age estimates based on the cave stratigraphy and associated vertebrate fossils place the nests at about 20,000 years old. Because the cave did not preserve insect bodies, the authors could not assign the nests to a living species; instead they described the trace fossil as Osnidum almontei, honoring the scientist who first reported the cave. The team notes that the behaviour could represent either an extinct lineage or an undocumented nesting habit in extant bees.
Analysis & Implications
The bone‑nesting record expands the behavioural repertoire known for bees and highlights the role of trace fossils in reconstructing paleoecology. If ground‑nesting bees repeatedly used bone cavities in a cave, it implies local ecological conditions—stable humidity, shelter from rain and predators—that made such sites advantageous. These microhabitats would have buffered brood from temperature and moisture extremes while concentrating resources for nesting across generations.
On an island biogeography level, the find underscores how limited sampling and preservation bias can obscure behavioural diversity. Amber captures older lineages and preserves body parts; cave and sedimentary contexts may better record ephemeral behaviours such as nesting site choice. For conservation and evolutionary studies, recognizing such behaviours in the past helps frame how insular pollinator communities adapted to fluctuating environments.
Practically, the discovery affects how curators and paleontologists inspect museum specimens. The authors stress that bones and other substrates can retain small‑scale structures that illuminate interactions between invertebrates and vertebrate remains. Future surveys that combine micro‑CT scanning and targeted sampling of cave sediments could reveal similar traces on other islands or mainland sites.
Comparison & Data
| Record type | Approx. age | Preservation | Typical context |
|---|---|---|---|
| Bone brood cells (this study) | ~20,000 years | Mineralized sediment in tooth sockets | Limestone cave deposits, protected microclimate |
| Caribbean bee body fossils (amber) | ~20 million years | Insect bodies in amber | Forest resin deposits |
| Modern ground‑nesting bees | Present | Soil burrows, plant stems | Open ground, shaded soils |
The table places the new bone‑nest record between older amber fossils and modern observations, illustrating how different preservational pathways capture different aspects of bee history. The cave context yields behavioural evidence absent from amber, while amber provides anatomical detail that the cave deposit lacks. Together these datasets offer a more complete picture of past pollinator diversity.
Reactions & Quotes
“It was very surprising to find invertebrate nesting traces in that cave,”
Lázaro Viñola‑López (Field Museum postdoctoral researcher, lead author)
Viñola‑López emphasized the unexpected nature of the find and the value of close inspection of fossil material. He noted that what looked like simple sediment fills turned out to be structured brood cells once scanned.
“This adds to the record of ‘hidden biodiversity,’”
Stephen Hasiotis (University of Kansas, geology and ichnology expert, commentary)
Hasiotis, not involved in the study, pointed out that trace fossils can reveal ecological roles and behaviours that body fossils miss, and that cave microclimates likely promoted repeated nesting.
“Insects have been adapting for hundreds of millions of years; this is another reminder of their behavioural flexibility,”
Anthony Martin (Emory University, environmental sciences)
Martin highlighted the evolutionary perspective: ground‑nesting lineages have long demonstrated adaptability, and unexpected nesting sites provide new data points for understanding that history.
Unconfirmed
- Which exact bee species made the nests remains unknown because no insect bodies were preserved in the cave deposits.
- Whether bone‑nesting and cave‑nesting behaviours persist among modern island bee populations on Hispaniola or nearby islands has not been established.
- The precise climatic or ecological triggers that led bees to select bone cavities over more typical substrates remain inferred rather than directly demonstrated.
Bottom Line
The discovery of mud‑lined bee brood cells within fossilized bone cavities on Hispaniola broadens our understanding of bee behavioural diversity and the types of evidence that preserve in the fossil record. The trace fossil Osnidum almontei documents repeated, multi‑generational nesting in protected cave microhabitats about 20,000 years ago, a behaviour not previously recorded in Caribbean cave deposits.
Beyond the specific find, this study is a methodological reminder: careful micro‑examination of existing museum specimens and targeted imaging techniques can reveal unexpected interactions between organisms. Follow‑up field surveys and targeted sampling on Hispaniola and neighboring islands could determine whether similar nesting strategies existed elsewhere or persist today.
Sources
- CNN (news report summarizing the study and interviews with researchers)
- Royal Society Open Science (peer‑reviewed journal; study published 17 December 2025)
- Field Museum of Natural History (museum; affiliated researchers and specimen curation)
- Florida Museum of Natural History (museum/press releases related to Caribbean fossil research)