The discovery that bumblebee queens could shake it off and emerge unscathed after more than a week submerged in water stunned scientists back in 2024.
Now, a new paper reveals how they do it. Included in the bumblebee survival toolkit is the remarkable ability to extract oxygen from the water around them – literally allowing them to breathe underwater temporarily.
It's a skill set that can help the heart of a colony weather a crisis such as a flooded burrow, allowing her to survive and rebuild when conditions are more stable. And its discovery suggests that some species may have hidden reserves of resilience against environmental extremes.
"Our findings," writes a team led by evolutionary physiologist Charles Darveau of the University of Ottawa in Canada, "reveal a remarkable flooding-tolerance strategy and provide a foundation for exploring the limits, mechanisms, and ecological significance of underwater survival in terrestrial insects."
Every winter, some insect species hibernate in a period of suspended development and metabolism known as a diapause. For some bumblebee queens, that means finding a safe, snug burrow, nestling in, and hitting the snooze button.
Burrows do not always remain safe and snug, though. Underground resting places can be vulnerable to flooding, and a bumblebee in diapause is too sluggish to respond with the alacrity that such an emergency would demand.
Weather events such as heavy rain, snowmelt, and rising water tables can all inundate a bee burrow, not necessarily regularly, but unpredictably, and with enough risk that at least one North American species, Bombus impatiens, appears to have adapted.
In 2024, scientists revealed that B. impatiens queens have a high rate of survival after up to a week submerged in water – around 90 percent.
Now, we finally get to find out how they did it: through a combination of underwater respiration, anaerobic metabolism, and "profound metabolic depression" – a state of extremely minimal metabolic function.
In laboratory experiments on dozens of queens in winter diapause, the researchers submerged the bumblebees in cold water and monitored their metabolism and gas exchange.
Gas exchange was measured in the water in which the bees were submerged, and in the air in the chamber above the water. The researchers tracked carbon dioxide and oxygen levels, and found that the former rose minutely, while the latter fell. This is consistent with respiration – the bees were taking in oxygen from the water and expelling carbon dioxide.
Meanwhile, submerged bees displayed a buildup of lactate. When the body can't get enough oxygen, cells switch to a metabolic process that generates energy without oxygen. Lactate is a byproduct of this anaerobic metabolism.
Finally, that metabolism is pushed to the bare minimum required for survival. Diapause already slashes a queen's metabolism by more than 95 percent. Submersion slashes it even further. Using carbon dioxide as a proxy for metabolism, we can see the drop.
Before submersion, diapausing bees were producing around 15.42 microliters of carbon dioxide per hour per gram of body mass. After eight days underwater, this production rate had dropped to 2.35 microliters, or about one-sixth of its original value.
Together, these processes allow the queens to take in oxygen from the water around them while keeping their energy needs extremely low.
Related: This Is The First Animal Ever Found That Doesn't Need Oxygen to Survive
It's a very tidy trick, although some things still aren't clear. The researchers did not ascertain how B. impatiens extracts oxygen from the water; they believe the queens make use of a physical gill, a thin layer of trapped air that exchanges gases with the water, but have yet to confirm this.
They also want to know the limitations of this extraordinary survival power.
"Future studies manipulating water conditions and the likely physical gill, alongside detailed recovery analyses, will further clarify the adaptations enabling queens to withstand extended submersion," they write.
The research has been published in the Proceedings of the Royal Society B: Biological Sciences.