In most bumblebee species, the queen spends the winter buried in a small cavity about the size of a grape. For six to nine months, they enter a deep sleep-like state called diapause, waiting for spring.
As climate change intensifies rainfall in many regions, overwintering queen bees face an increased risk of unstable underground conditions, including flooding.
Therefore, it is good that these insects can survive underwater for several days without drowning. Remarkably, our new research reveals that they achieve this through the process of continuously breathing while submerged underwater for up to eight days.
It started with a lab accident
We initially discovered that overwintering bumblebee queens can survive accidental submersion.
During an experiment at the University of Guelph, part of the tube in which the queen was overwintering in the laboratory refrigerator accidentally filled with water.
At first we thought the queens were dead. However, once the water was removed, it started moving and quickly recovered. This suggests that bumblebee queens may be able to survive submersion.
(Charles-Antoine Darvaux)
Therefore, we designed a tracking experiment with 143 common bumblebee queens (Impatient bomb statement).
This confirmed that it was no fluke. Queen bees tolerated complete submergence for up to a week.
This raised the interesting question of how this terrestrial insect pollinator is able to survive in water. Answering that required a different approach. We needed to study their physiology.
center of colony
The queen bee is the center of a bumblebee colony and the only chance to produce the next generation. In the summer, we often hear the buzz of worker birds visiting flowers, but we rarely see the queen bee. They spend most of the season in the nest, laying eggs that become worker bees, and in late summer a male and a new queen are born.
When winter comes, most members of the colony die and only the newly born queen survives. After mating, these new queens disperse and go underground, each settling into a small cavity where they enter diapause.
When spring finally arrives, the queens who have survived their long underground sleep emerge from their burrows and begin the important task of establishing a new colony.
(Lucas Borg-Darveau/Minutes B)
Read more: Worker bees sense infection in queen, triggering revolt
breathing underwater
To understand how these queens are able to survive submersion, we studied their respiration and metabolism in our lab at the University of Ottawa.
During dormancy, the queen bee is already in extreme energy-saving mode. The energy needed to stay alive (called metabolic rate) is reduced by more than 99 percent. When submerged, the required energy is further reduced. This low oxygen requirement makes underwater breathing possible.
But how did they determine whether the queen was actually breathing underwater? One way is to measure the gases exchanged with the surrounding water. I did this and the results were amazing. The queen continued to consume oxygen and release carbon dioxide underwater during the eight-day submersion period.
(Sabrina Rondeau)
Many aquatic insects use simple tricks to breathe underwater. A thin layer of air sticks to your body, allowing you to use your normal air breathing system, the tracheal system. Oxygen from the surrounding water slowly diffuses into this air layer. Bumblebee queens probably rely on the same mechanism.
Still, underwater respiration alone cannot fully meet the queen’s energy needs. To fill this gap, the queen also produces energy through anaerobic metabolism, a process that does not require oxygen. This pathway produces lactic acid, which was detected in queen bees during submersion.
These physiological tricks allow queens to survive underwater, but they come at a cost. After the queen emerges, it takes several days to recover and expends far more energy than she would have had she not taken the plunge.
Read more: Stay active even in subzero temperatures: How do salamanders stay active in winter?
unexpected resilience
Queen bumblebees spend the winter alone, buried underground and rely on stored energy to survive until spring. Their ability to withstand several days of submergence and even breathe underwater shows an unexpected resilience to one of the perils of life underground.
This is important because bumblebee colonies are completely dependent on the survival of the overwintering queen. If a queen dies during the winter, the colony she was supposed to establish the following spring no longer exists.
This ability to survive submersion may play an important, hitherto overlooked role in the resilience of endangered bumblebee populations.
Even for well-known and relatively well-studied insects like bumblebees, there is still much to learn about the surprising ways they cope with environmental challenges.
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