Bumblebee Queens Survive Underwater Using a Remarkable Oxygen Strategy

The revelation in 2024 that bumblebee queens could endure more than a week underwater and emerge unharmed astonished scientists.

A new study has now explained how they manage it. The bumblebee survival toolkit includes an exceptional capacity to draw oxygen from the surrounding water – effectively enabling them to breathe underwater for a limited time.

This collection of abilities could help the key individual in a colony survive a disaster such as a flooded burrow, so she can live on and rebuild once conditions settle. The finding also indicates that certain species may possess previously unseen resilience to environmental extremes.

"Our findings," writes a team led by evolutionary physiologist Charles Darveau of the University of Ottawa in Canada, "reveal a remarkable flooding-tolerance strategy and provide a foundation for exploring the limits, mechanisms, and ecological significance of underwater survival in terrestrial insects."

Diapause and the risk of flooded burrows

Each winter, certain insect species enter diapause, a phase of suspended development and metabolic activity. For some bumblebee queens, this involves locating a protected, cosy burrow, settling inside, and effectively pressing the snooze button.

Yet burrows cannot always stay protected and cosy. Underground shelters may be exposed to flooding, while a bumblebee in diapause is too sluggish to react with the speed such a crisis requires.

Severe weather, including heavy rainfall, melting snow, and rising water tables, can all flood a bee burrow. These events may not happen often, but they are unpredictable; the risk appears substantial enough that one North American species, Bombus impatiens, has adapted.

In 2024, scientists reported that B. impatiens queens survived immersion in water for as long as a week at a high rate – around 90 percent.

How bumblebee queens survive underwater

Researchers can now explain how this happened: through a combination of underwater respiration, anaerobic metabolism, and "profound metabolic depression" – a state in which metabolic activity is reduced to an extremely low level.

For laboratory tests, the team placed dozens of queens in winter diapause in cold water, then observed their metabolism and gas exchange.

They measured gas exchange both in the water surrounding the submerged bees and in the air within the chamber above it. By monitoring oxygen and carbon dioxide concentrations, the scientists found a tiny rise in the latter and a fall in the former. That pattern is consistent with respiration: the bees absorbed oxygen from the water and released carbon dioxide.

At the same time, the submerged bees accumulated lactate. When the body does not receive sufficient oxygen, cells change to an energy-producing metabolic process that operates without oxygen. Lactate is produced as a by-product of this anaerobic metabolism.

Metabolism reduced to survival levels

Their metabolism is also cut back to the absolute minimum necessary for survival. Diapause already reduces a queen's metabolism by more than 95 percent, and submersion lowers it still further. Carbon dioxide serves as a proxy for metabolism and reveals this decline.

Before they were submerged, bees in diapause produced around 15.42 microliters of carbon dioxide per hour per gram of body mass. Following eight days underwater, the production rate had fallen to 2.35 microliters, or roughly one-sixth of the initial level.

Combined, these processes let the queens obtain oxygen from the water around them while keeping their energy demands exceptionally low.

It is an impressively neat strategy, although some details remain unresolved. The researchers did not determine how B. impatiens removes oxygen from water. They suspect that queens use a physical gill – a thin layer of trapped air that exchanges gases with the water – but this has not yet been confirmed.

The team also hopes to establish the limits of this remarkable survival capability.

"Future studies manipulating water conditions and the likely physical gill, alongside detailed recovery analyses, will further clarify the adaptations enabling queens to withstand extended submersion," they write.

The research was published in the Proceedings of the Royal Society B: Biological Sciences.