In many species of bumblebees, the queens spend their winters buried underground in a small pit the size of a grape. For six to nine months, they enter a deep sleep-like state called diapause, waiting for the season.
As climate change brings heavy rainfall to many areas, these overwintering queens face increasing risks from unstable underground conditions, including flooding.
Well, it’s a good thing that these insects can survive for days underwater without drowning. Amazingly, our new research reveals that they achieve this by breathing continuously while underwater for up to eight days.
It started with a lab accident
Initially we discovered that bumblebee queens can survive accidental submersion.
During experiments at the University of Guelph, some of the tubes that the ladies were spending the winter in the lab’s refrigerator accidentally filled with water.
At first, we thought the ladies were dead. But after they took out the water, they started to move and soon recovered. This suggested that bumblebee queens can survive underwater.
(Charles-Antoine Darveau)
Thus, we conducted a retrospective analysis involving 143 common oriental bumblebee queens (An impatient bomber).
This confirmed that it was not a leak: the ladies endured complete immersion for up to a week.
This raised an interesting question: How can this terrestrial insect pollinator survive underwater? Answering it required a different approach – we needed to study their physiology.
The heart of the colony
The queen is the heart of the bumblebee colony and its only chance to produce the next generation. Although we often hear the noise of the workers visiting the flowers during the summer, the ladies are rarely seen. They spend most of their time in the nest, laying eggs that will become workers, and later in the summer, new males and queens.
When winter comes, most members of the colony die and only the newly produced queens survive. After mating, the young queens disperse and burrow underground, each settling into a small hole where they enter diapause.
When spring returns, the queens that survived their long underground slumber emerge from their burrows and begin the important task of establishing a new colony.
(Lucas Borg-Darveau/Proceedings B)
Read more: Worker honey bees can detect infection in their queen, leading to rebellion
Breathing underwater
To understand how these ladies can survive underwater, we studied their respiration and metabolism in our laboratory at the University of Ottawa.
During diapause, queens are already in an extreme state of energy conservation. The energy they need to stay alive (known as their metabolic rate) drops by more than 99 percent. When submerged, energy needs drop even more. With such small oxygen requirements, underwater breathing is possible.
But how did we know if the ladies breathe underwater? Another way is by measuring the gases exchanged with the surrounding water. We did this and the results were amazing: the queens kept using oxygen and exhaling carbon dioxide underwater throughout the eight days of immersion.
(Sabrina Rondeau)
Many aquatic insects use a simple trick to breathe underwater. Thin air clings to their body, allowing them to use their normal breathing system – the tracheal system. Oxygen from the surrounding water slowly diffuses into this air space. It is possible that Bumblebee queens rely on the same mechanism.
However, underwater breathing alone does not fully meet a queen’s energy needs. To bridge the gap, queens also produce some energy through anaerobic metabolism – a process that does not require oxygen. This process produces lactic acid, which we found in the ladies during the immersion.
These physiological tricks allow queens to survive underwater, but they come at a cost. After reawakening, the ladies spend several days recovering, using more energy than they would have if they hadn’t pushed themselves.
Read more: Below the ice but still moving: How salamanders stay active in winter
Unexpected comfort
Bumblebee Queens spend the winter alone, buried underground and relying on stored energy to survive until spring. Their ability to withstand days of submersion – even breathing underwater – reveals an unexpected resilience in one of the perils of underground life.
This is important because bumblebee colonies are completely dependent on the survival of overwintering queens. If the queen dies during the winter, the colony she would have established during the following spring will no longer exist.
This ability to survive underwater may play an important – and previously overlooked – role in stabilizing threatened bee populations.
Even in the case of common and well-studied insects such as bumblebees, there is still much to be learned about the surprising ways in which they deal with environmental problems.
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