Every spring, fertilized bumblebee queens emerge from hibernation and establish new colonies. During the winter, their underground shelters are often flooded by meltwater or rain. Research conducted in 2024 has shown that bumblebees can survive underwater for up to a week. Recent experiments have helped uncover the physiological mechanisms behind this remarkable ability.

Adaptation to Winter Conditions

Winter in temperate regions poses a serious challenge for many animals. To survive the cold and food shortages, insects have developed special mechanisms for seasonal adaptation. One such mechanism is diapause—a dormant phase during which metabolism slows down, allowing them to go without food for extended periods. In this state, their bodies require minimal energy, they do not reproduce, and growth nearly stops, but vital functions are maintained at the lowest possible level.

Hibernation of Bumblebee Queens

After mating, the future queen digs a small chamber in the ground, up to 15 centimeters deep, and enters a dormant state for six to nine months. She is the only member of the colony to survive the winter; worker bees and males die before the onset of cold weather. The underground shelter protects her from frost but not from other threats such as parasites, mold, pesticides, or flooding from meltwater or groundwater.

Experimental Studies

To study the impact of harsh climatic conditions on insects capable of diapause, a series of experiments was conducted with Bombus impatiens queens. In the laboratory, winter conditions were simulated: queens were placed in test tubes with soil and kept in a refrigerator. Due to condensation, some of the tubes filled with water, and four queens were completely submerged. All of them survived.

Further experiments with more than a hundred queens confirmed that bumblebees can survive underwater for up to seven days.

Physiological Mechanisms of Survival

To understand how bumblebees survive underwater, researchers used special laboratory chambers and sensors to measure the respiration of Bombus impatiens queens. It was found that even underwater, the insects continued to consume oxygen and release carbon dioxide. The instruments recorded a small but steady production of carbon dioxide, and the level of dissolved oxygen in the water decreased, indicating underwater respiration.

The secret lies in diapause: during this period, metabolism drops by 99%, and the organism uses minimal energy. Underwater, metabolism slows even further, so even a small amount of oxygen absorbed from the water is enough to sustain life. Any energy deficit is compensated by anaerobic metabolism.

In the tissues of submerged queens, lactate (lactic acid)—a byproduct of metabolism when oxygen is scarce—accumulates. A similar process occurs in humans during intense physical activity.

Recovery After Flooding

After being removed from the water, the lactate level in the bumblebees’ bodies gradually decreased and returned to normal in about seven days. In the first days after emerging from the water, their metabolism spiked to restore strength, then returned to typical diapause levels. Within two or three days, the queens began to move, but full metabolic recovery took up to a week.

Underwater Respiration Mechanism

It is still unclear exactly how bumblebees obtain oxygen underwater. Some insects use breathing tubes or carry an air bubble with them. It is believed that bumblebees have so-called physical gills—a thin layer of air held on the body surface by numerous hairs. This air layer forms a boundary between the body and the water.

Oxygen dissolved in the water gradually diffuses through the air layer into the respiratory openings (spiracles), and then into the tracheae, which deliver air to the tissues. In the opposite direction, carbon dioxide is expelled from the body into the water.

Evolutionary Aspect

The underwater respiration mechanism in bumblebees is explained by their evolutionary history. The ancestors of modern bumblebees appeared 25–40 million years ago, during a period of dramatic climate change, and adapted to cold arctic and alpine regions where meltwater is common. This created the need to adapt to new environmental conditions.

It is believed that the ability to breathe underwater is widespread among most of the 250 bumblebee species found on Earth.

The scientific study was published in the journal Proceedings of the Royal Society B.