Researchers believe a sudden shift in weather may have caused the sudden mass death of these Eucera bees.
A strange series of events 3,000 years ago led hundreds of bees to be preserved in sealed cocoons, and now researchers have a theory as to why.
The bees were first discovered in 2019, when a research team was exploring the coastline of southwest Portugal as part of an analysis of how the area’s ecosystem has changed over time. During the analysis, they came across hundreds of bees, which for millenniums had sat in their own cocoons, preserved in layers of sediment.
As paleontologist Carlos Neto de Carvalho told The New York Times, whatever happened 3,000 years ago, it was “an unlucky night for hundreds of adult bees that were ready to leave their cocoons.”
Unlike European honeybees, which live in a hive, these were Eucera bees, which spend most of their lives gestating underground and feeding on pollen left by their mothers. They only live for about one year, and only emerge from their subterranean homes for a few weeks, when their favorite flowers bloom.
“Hundreds of bees preserved in their brood nests just before exiting means that something catastrophic happened for them in what is now the sunny coast of Portugal,” Neto de Carvalho said.
But finding bee, or any insect, exoskeletons preserved for so long is a rarity in its own right. Bee exoskeletons are made of chitin, a fibrous substance that also forms the cell walls of fungi, which decomposes rather quickly after the animal dies.
More often, researchers find trace fossils of bees and other insects — markings that show a record of biological activity in an area, but no remains from the animal itself. These ichnofossils, as they are called, could be footprints embedded in a fossilized rock, for example, or other imprints.
These bees, however, were found wrapped in what Neto de Carvalho called an “organic mortar.” They were still lined and sealed within a silk-like thread created by the mother bee, and over the course of millennia, this waterproof casing protected the bees’ brood cells from the surrounding environment, preventing the decomposition of the chitin that makes up their exoskeletons.
The end result: perfectly intact bees.
Still, although researchers had determined how the bees were preserved for so long, they still had no idea what had led to their untimely demise in the first place.
In a recent study published in the journal Papers in Paleontology, they offered up a few theories.
“Although the cause of mass mortality remains a mystery, oxygen depletion due to sudden flooding of the nesting substrate and consequent or overnight temperature drop, just before emergence, are plausible causes,” they wrote.
There was one major flaw with each of these theories, however: the bees had plenty to eat. Whereas a significant drought or flood would have likely limited the bees’ food supply, the amount of pollen stored inside the brood cells showed that the bees were not starved for food.
The current hypothesis, according to Neto de Carvalho, is a sudden shift in weather.
“We assume that a sudden drop to freezing temperatures in that early spring was responsible for the massive death at the soil level,” he said.
Neto de Carvalho has also adopted an optimistic outlook on the bees’ situation. While it was certainly tragic for hundreds of bees to lose their lives before they really had a chance to live them, it should also be noted that there are more than 25 species of Eucera-like bees living in Portugal today. If anything, this study shows that bees are able to adapt to changing climate conditions and withstand otherwise tumultuous circumstances.
“We expect this discovery will bring us more information about how these animals became resilient to climate change,” Neto de Carvalho said. “The Eucera bee mummies can be considered, therefore, a message of hope in this world of climatic chaos we are living presently.”
After reading about these 3,000-year-old preserved bees, read about when researchers found an immaculately preserved prehistoric baby bird in amber. Or, read about the mummified Ice Age wolf pup and caribou found in Canadian permafrost.