Hibernating Bumblebee Queens Can Survive Underwater for Up to a Week, Study Finds

Researchers discovered the insects’ unexpected superpower during an accidental laboratory snafu

a bumblebee in profile on a yellow flower
Hibernating common eastern bumblebee queens survived for a week while submerged underwater in a lab. Rhododendrites via Wikimedia Commons under CC BY-SA 4.0

Bumblebees may be more resilient than previously thought: Hibernating queen bees can survive for up to a week underwater, researchers report Wednesday in the journal Biology Letters.

Researchers learned of the insects’ surprising superpower by accident. The discovery unfolded while ecologist Sabrina Rondeau was investigating the effects of pesticide residue on common eastern bumblebees (Bombus impatiens) in a laboratory at Canada’s University of Guelph in 2021. More specifically, Rondeau was studying hibernating queen bees by keeping them in soil-filled tubes in a refrigerator, which mimics their natural winter hibernation environment.

One day, when she opened the refrigerator, she saw that some of the tubes were filled with water from condensation—and that four of the queens were totally submerged. Rondeau was devastated.

“I kind of freaked out,” she tells New Scientist’s Sofia Quaglia. “I was sure the queens were dead.”

But when she removed the queens from the water, they began moving around again.

“[It was] really surprising,” study co-author Nigel Raine, an environmental scientist at the University of Guelph who also participated in the 2021 pesticide research, tells CNN’s Jack Guy. “These are terrestrial organisms; they’re not really designed to be underwater.”

Rondeau, who is now at the University of Ottawa, suspected the queens’ survival wasn’t a one-off occurrence. She set up an experiment involving 143 common eastern bumblebee queens, placed in individual, soil-filled vials in the refrigerator. Seventeen queens served as the control group and were kept dry during hibernation, while the others were exposed to various levels of water for different amounts of time.

For either eight hours, 24 hours or one week, some of the bees were totally submerged, while others were left floating on top of the water. After the allotted time had passed, the bees were removed from the water and allowed to continue hibernating under normal conditions.

But after just one day back in dry vials, the formerly wet, bedraggled bees were “fluffy again, beautiful, like nothing happened,” Rondeau tells Science News’ Darren Incorvaia.

Of the 21 bees that were submerged for a full week, 17 were still alive eight weeks later—a survival rate of 81 percent. This was not far off from the survival rate of the control group: 15 of the 17 bees that were never submerged, or 88 percent, survived to eight weeks.

Close-up of bee
A common eastern bumblebee Ryan Hodnett via Wikimedia Commons under CC BY-SA 4.0 DEED

Researchers don’t fully understand why the submerged bees didn’t drown, but the findings make sense in the context of bee hibernation. Every fall, as temperatures begin to drop ahead of winter, male and worker bees die off, while queens burrow into the ground and hibernate. They can spend roughly eight months underground, waiting for spring to arrive so they can emerge and start new colonies. During that time, their metabolism plummets and they need very little oxygen.

Hibernating in the ground can be risky, since it leaves bumblebees in the path of flooding from potential extreme weather events. But, it turns out, hibernating queens may have evolved to withstand this possibility. This is “very encouraging news,” especially in the context of human-caused climate change, which may be making extreme weather worse, Rondeau tells the Globe and Mail’s Ivan Semeniuk.

“One-third of all bumblebee species around the world are in decline right now, and so if we are able to discard flooding as being a potential threat to bees, then we can focus our attention on other threats that we know for sure are harming them,” she adds.

Dave Goulson, a biologist at the University of Sussex in England who was not involved with the research, echoed that sentiment, adding that flooding “seems to be one small aspect of climate change that we need not worry about” with these bees, he tells the Guardian’s Nicola Davis.

Still, many questions remain unanswered, for instance, does being submerged during hibernation have any longer-term ripple effects, such as affecting the queens’ ability to start new colonies in the spring? Can other bees survive drowning, too, or just this species? And what’s the upper limit for how long bees can survive underwater?

The findings show “how little we know—and how much there is to learn—about the bumblebee life cycle,” says Elizabeth Crone, a biologist at the University of California, Davis, who was not involved in the research, to Science News.

“Their interactions with flowers are one of the best studied phenomena in ecology,” she adds to the publication. “In contrast, we know very little about their nesting, hibernation and reproduction.”

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