Ancient bees laid eggs inside bones
Bees are frequently associated with large queen colonies comprising hundreds or even thousands of insects. In reality, this is usually not the case.
“Most bees are solitary. They lay their eggs in small cavities and leave pollen for the larvae,” explained paleontologist Lazasro Viñola López. “Some species of bees dig holes in wood or ground, or use empty structures to make their nests.”
Viñola López, a researcher at the Field Museum in Chicago, added that some European and African species even build nests inside vacant snail shells. That said, a hive inside a bone is new, even to seasoned researchers. Estimated to be around 20,000 years old, this newly discovered specimen is also the first known example of such a dwelling, past or present. The results are detailed in a study published on December 16 in the journal Royal Society Open Science.
Researchers discovered this unique discovery while exploring the numerous limestone caves that dot the southern Dominican Republic. Sinkholes are common on the Caribbean island of Hispaniola and are often so well protected from the elements that they function like underground time capsules.
These windows into the past are largely thanks to the work of the island’s owls. Predatory birds often make their nests inside these caves, where they regularly spit out owl pellets filled with the undigested bones of their prey. Over thousands of years, these layers of bone fossilize on top of each other in the carbonate layers created by rainy periods. However, getting a first-hand look at these remains is not for the faint of heart.
“The initial descent into the cave is not too deep: we attach a rope to the side and then rappel down,” explained Viñola López. “If you go in at night, you see the eyes of the tarantulas that live inside.”
After passing the large spiders through about 33 feet of underground tunnel, paleontologists began finding various fossils. Many belonged to rodents, but there were also bones from birds, reptiles and even sloths, making a total of more than 50 different animal species.
“We think this was a cave where owls lived for many generations, perhaps for hundreds or thousands of years,” Viñola López said. “The owls would go out to hunt, then come back to the cave and vomit pellets. [found] fossils of the animals they ate, fossils of the owls themselves and even turtles and crocodiles that may have fallen into the cave.
While cleaning her finds, Viñola López noticed a smooth, almost concave sediment in one of the tooth sockets of a mammalian jaw fossil. Dirt doesn’t normally accumulate this way in fossils, but then Viñola López started finding other examples.
“I thought, ‘Okay, there’s something weird here,'” he recalls.
The mysterious fillings reminded Viñola López of some fossilized wasp cocoons he had examined during a student dig in Montana. After scanning the specimens with CT, his team noticed that the sediment structures appeared almost identical to the fossils from his college days. Some even still contained grains of pollen that mother bees probably locked away in individual nests as food for their larvae.
Although the nests did not contain any fossilized insects, this was to be expected. The caves, although protected from the outside world, remain extremely humid and hot, conditions not conducive to the preservation of delicate exoskeletons.
“As we did not find any bee bodies, it is possible that they belong to a species still alive today. Very little is known about the ecology of most of the bees on these islands,” Viñola López said.
The fossilized bone nests are the first of their kind ever discovered, even in present-day ecosystems. There may be other examples, but it is also possible that caves provide a unique environment for bees. Without much soil on the area’s limestone, the insects may have resorted to caves for nesting. There, bones discarded by owls provided a convenient alternative habitat for bee larvae.
“This discovery shows how strange bees can be: they can surprise you,” said Viñola López. “But it also shows that when you look at fossils, you have to be very careful.”
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