Throughout winter, bumble bee queens lie buried underground in diapause, in a hibernation-like state, in a form of overwintering. But as snow melts and heavy rains soak the ground each spring those underground chambers fill with water, it was assumed that the bees who hadn't yet awoken from their slumber, drowned. Now new research from the University of Ottawa shows that these queens can survive being submerged for over a week, thanks to a mix of physiological mechanisms.
The study, led by Professor Charles-Antoine Darveau , full professor in Comparative Physiology in the Department of Biology at uOttawa, reveals how these vital pollinators' remarkable flooding-tolerance strategy may be crucial as extreme weather events become more frequent.
Life underground and underwater
Bumble bee queens spend winter in diapause, a hibernation-like state, buried in the soil. When spring flooding occurs, they can become trapped underwater.
"This study started from a discussion with my co-author and postdoctoral researcher, Sabrina Rondeau, whose recent findings showed that these queens can survive submersion for over a week, which is extraordinary for a terrestrial insect," says Professor Darveau. "We wanted to understand how that's even possible."
To find out, the research team, including honours student Skyelar L. Rojas, recreated winter conditions in the lab. Queens were placed in diapause for four to five months before being submerged underwater for eight days. Throughout the experiment, researchers monitored their metabolic rate and physiological changes.
Breathing underwater
What they discovered was striking. Even underwater, the queens continued exchanging gases. In effect, breathing while maintaining an exceptionally low metabolic rate.
"The first key is metabolic depression," explains Professor Darveau. "Their metabolism is already extremely low during diapause. That low energy demand makes survival possible."
But that wasn't the whole story. The team also detected significant accumulation of lactic acid in the bees' bodies, evidence that they were producing energy without oxygen through anaerobic metabolism.
"They're not relying on just one strategy," Darveau says. "They combine underwater gas exchange with anaerobic metabolism. That flexibility is what allows them to survive these extreme conditions."
The cost of survival
Surviving underwater comes at a price. After eight days of submersion, once the queens were removed from the water, their metabolic rate spiked dramatically for two to three days.
"That surge in metabolism coincides with clearing the accumulated lactate," reveals Professor Darveau. "It's essentially a recovery phase. After about a week, their metabolism returns to normal diapause levels."
Weathering climate change
Bumble bee queens are the founders of future colonies. If they don't survive winter and early spring, entire colonies are lost.
"This study shows how resilient these pollinators are," Darveau clarifies. "Understanding these mechanisms helps us predict how bumble bee populations might cope with increasingly frequent spring floods."
As climate change continues to reshape seasonal patterns, the ability of a tiny, hibernating queen to quietly endure days underwater may prove more important than ever.
The study, titled " Diapausing bumble bee queens avoid drowning by using underwater respiration, anaerobic metabolism and profound metabolic depression ", is published in The Royal Society Publishing .
