Hibernating bumblebee queens have a superpower: Surviving for days underwater

It’s not easy being a queen — a bumblebee queen, that is. To start her colony in the spring, an expectant queen must first survive the winter by hibernating alone in the soil, where she’s vulnerable to hazards like floods.

It turns out these bee queens are royally up to the task. In a serendipitous discovery, researchers have found that hibernating bumblebee queens can survive being submerged in water for up to a week.

Bee biologists Sabrina Rondeau and Nigel Raine were studying how hibernating queens respond to pesticide exposure (SN: 3/29/12). Condensation in the refrigerator storing the dormant bees in Raine’s lab at the University of Guelph in Canada accidentally caused four of the vials housing queens to flood, the pair describe April 17 in Biology Letters.

“I was very concerned at first,” says Rondeau, now at the University of Ottawa. “I thought, of course, they were dead.” But to her great surprise, when she picked the queens up with forceps they started fidgeting — undeniably alive.

Rondeau and Raine decided to test more rigorously just how waterproof bumblebee queens are. They gathered 143 common eastern bumblebee queens (Bombus impatiens) left over from another experiment (these bees are available commercially, and weren’t collected from the wild). Seventeen queens served as controls and weren’t submerged underwater, while the others were either submerged or left floating on the water’s surface for either eight hours, 24 hours or one week. All the bees were housed in individual vials and stored at cold hibernation temperatures.

This was meant to mimic possible real-world flooding scenarios, where a queen’s hibernation chamber could potentially be filled with water or only partially submerged. How often that happens is unknown. Observations of bumblebees overwintering in the wild are scarce, but queens have been found to generally prefer sloped ground and sandy soils that would not be prone to flooding. Even so, it seems the insects are prepared for disaster.

It turned out that the four queens who survived accidental fridge flooding were hardly outliers. Of the 21 queens that were submerged for seven days and then allowed to resume hibernating, 17 were still alive eight weeks after their aquatic ordeal. This rate of survival was not statistically different from that of the 17 bees that were never submerged — 15 of them survived to eight weeks.  

When first pulling the queens out of the water, Rondeau says they looked like a bee that you’d fish out of a swimming pool. But after a day back in the refrigerator, “they are fluffy again, beautiful, like nothing happened,” she says. “Extremely surprising.”

The finding raises many more questions, Raine says. “Does it affect their ability to found colonies? Does it affect reproductive success of the colony?”

There’s also the question of how the queens manage to survive being underwater for so long. Many adult insects have adaptations to help them avoid drowning, like closing their spiracles — the body openings they breathe through — to prevent water from getting in. Rondeau suspects that the lowered metabolism of hibernating queens also helps, as they can go longer with their spiracles closed than they could if they were fully awake and active.

“What it really shows is 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. “Their interactions with flowers are one of the best studied phenomena in ecology. In contrast, we know very little about their nesting, hibernation and reproduction.”