Bumblebees warm up carrying pollen, raising climate change questions – study

Carrying pollen is a workout that significantly increases the body temperature of bumblebees, researchers have found.

A new study suggests this new understanding of active bumblebee body temperatures raises questions about how they will be impacted by climate change.

The insects carry solid packets of pollen on their back legs, and while it might look like they move from flower to flower with ease, these packets can weigh up to a third of their body weight.

According to the new research, after accounting for environmental temperature and body size, the body temperature of bumblebees carrying pollen was significantly hotter than the temperature of bees that were empty-legged.

Specifically, the North Carolina State University study found that bee body temperatures rose 0.07C for every milligram of pollen they carried.

While fully laden bees were 2C warmer than unladen bees.

Malia Naumchik, a former applied ecology minor undergraduate and lead author of the study, said: “Getting warmer from carrying pollen could put bumblebees in the range of those stressful, critically hot temperatures.

“This has important implications for bumblebees and climate change. As environmental temperatures increase, the bees’ operational range of temperatures could shrink significantly.”

The body temperature of a bumblebee is mostly determined by the environment.

Among bees, bumblebees are exceptionally cold tolerant and will even shiver to warm up during cold days, but not much is known about how they tolerate heat.

Since pollen-laden bumblebees are hotter than unladen ones, this could mean carrying a full load of pollen on a hot day puts bees at greater risk of reaching the potentially lethal end of their temperature tolerance, the researchers suggest.

Pollen is crucial for every stage of a bumblebee’s life history, and experts say that without pollen, or enough pollen, colonies will not thrive – risking future colonies and the species as a whole.

This may also have implications for pollination in general, and could impact agriculture and ecosystems alike.

Elsa Youngsteadt, a professor in applied ecology and supervisor of the research, said: “We need to know how bumblebees may change their behaviour, to better understand how this could affect how much pollen they collect and how much pollination they perform during hot days.

“Whether it’s carrying smaller loads of pollen or foraging for shorter times, it could result in less pollen coming to the colony and fewer plants being pollinated.

“This is particularly important since bumblebees provide critical ecosystem services and are key pollinators for agriculture, especially in the United States and Europe.”

The findings are published in the Biology Letters journal.