Bumblebee Nests May Be Overheating With Rising Global Temperatures, Study Finds

Bumblebees are disappearing around the world. But so far, scientists can only speculate about what’s causing their demise, probing the effects of habitat loss, pesticides and disease.

Now, new research makes the case for another possible killer: rising global temperatures.

Across many different species of bumblebees and the various regions they inhabit, the insects thrive when their nests are between 82 and 89.6 degrees Fahrenheit, according to a new paper published Friday in the journal Frontiers in Bee Science. When nest temperatures reach 96.8 degrees or higher, however, bees struggle to survive, the findings suggest.

Researchers reached this conclusion after reviewing scientific literature dating back to the 1840s.

“It’s remarkable that all the way from the high Arctic to the tropics, bumblebees seem to have the same sort of nest temperature requirements,” says study co-author Peter Kevan, an environmental scientist at the University of Guelph, to New Scientist’s Corryn Wetzel. “If it gets too hot… it’s quite likely that they will die.”

Past research on honeybees has shown that hotter nest temperatures compromise the queens’ ability to reproduce and lead to smaller, less hardy worker bees. Scientists suspect heat likely has similar effects on bumblebees, which may help explain why they’re declining amid human-caused climate change.

Bees can cool down their nests by beating their wings like fans, but “if the air outside is too hot, that’s not going to help,” says Dave Goulson, a biologist at the University of Sussex in England who was not involved in the research, to the Guardian’s Sophie Kevany.

The findings are not surprising, given that bumblebees thrive in cooler places, including one species, Bombus polaris, that lives in the Arctic. Some bumblebees are already adapting, such as by moving to higher elevations, but that strategy, too, will only work for so long—unless humans halt the progression of climate change.

Some individual bees may be able to tolerate higher temperatures. But the researchers argue that bumblebee colonies should be viewed as “superorganisms,” meaning that they all rely on each other for survival and reproduction. If nests are too warm and larvae die off, that affects the entire colony.

Last year was the hottest on record, with global temperatures more than 2 degrees Fahrenheit higher than the 20th-century average. In addition, the ten hottest years since modern record-keeping began in 1850 have all occurred within the last decade. The United States is also coming off its warmest winter on record, with temperatures 5.4 degrees Fahrenheit above average.

Because so many different bumblebee species seem to thrive within the same temperature window, scientists suspect it will be very difficult for the iconic, black-and-yellow insects to adapt to this new normal.

“Excessively high temperatures are more harmful to most animals and plants than cool temperatures,” says Kevan in a statement. “When conditions are cool, organisms that do not metabolically regulate their body temperatures simply slow down, but when temperatures get too high, metabolic processes start to break down and cease.”

In addition to tackling climate change, the researchers say it’s still important to address other threats to the insects, like pesticides and habitat loss. Bees and many other pollinators play a vital role in the ecosystem by helping plants reproduce. Without pollinators, much of the world’s food supply would suffer.

More than 250 bumblebee species live around the world, including 49 in the United States. Already, some species are disappearing: Franklin’s bumblebee, which has not been seen since 2006, was added to the federal endangered species list in 2021, joining the rusty patched bumblebee, which has been listed as endangered since 2017.

Meanwhile, the American bumblebee population has declined by nearly 90 percent over the last two decades. Federal officials recently began considering whether to add the Southern Plains bumblebee to the endangered species list.

Sarah Kuta | READ MORE

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.