Bumblebees: Climate change may be 'overheating' wild bee nests - driving them closer to extinction

Climate change may be heating up bumblebee nests, a new study has warned, cooking the important pollinators’ larvae before they have the change to grow up.

In a new study by researchers from Canada’s University of Guelph, published in the journal Frontiers in Bee Science on Friday (3 May), scientists have identified rising heat as a potential culprit for the decline in bumblebee populations worldwide. This comes after the world has just experienced its hottest year on record - with experts already warning 2024 may be even hotter.

Wild bumblebees can be found in diverse habitats all over the world. Many species are unfortunately in decline, with scientists believing this was linked to the changing climate. However until now, the exact cause for this decline had been difficult to pinpoint.

By reviewing more than 180 years of research, lead author Dr Peter Kevan and his colleagues have discovered that all bumblebees appear to have an optimal temperature range for their nests, which allows their larvae to grow up healthy. This is about 28C to 32C. Bumblebees have a remarkable ability to regulate their temperatures, but Dr Kevan told SWNS that if the nest temperature rose above 35C, it could quickly prove lethal to their brood.

Because the characteristic appears to be common between so many species, it may mean the bumblebees will find it hard to adapt to rising temperatures, he said. “Excessively high temperatures are more harmful to most animals and plants than cool temperatures. 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. Death ensues quickly.

“The effect of high nest temperatures has not been studied very much, which is surprising,” he continued. “We can surmise that nest temperatures above the mid-30s Celsius would likely be highly detrimental and that above about 35C death would occur, probably quite quickly.”

Previous research has shown that higher nest temperatures compromise queen bee’s strength and reproductive ability, and lead to smaller worker bees, in poorer condition. Dr Kevan said that if heat was having a similar effect on bumblebees, then warming global temperatures could be directly leading to their decline.

Bumblebees do have some behavioural adaptations which allow them to thermoregulate, but he warned it may not be enough to deal with climate change. This was, in part, because bee colonies were “superorganisms”, where success depended on the colony as a whole surviving rather than it coming down to individual bees - even if that individual was more tolerant of heat.

The team is calling for more research into what they say is an understudied aspect of bumblebee ecology - nests and their shapes, the materials they’re made from, and how they cope with different temperatures. Dr Kevan added: “We hope that future scientists may take the ideas we present and apply them to their own research on bumblebee health and conversation.”

There are around 250 bumblebee species worldwide, and about 26 of them can be found in the UK. Unfortunately many of our local bees are now in trouble, and conservation charity Buglife believes two species to be extinct - while six have fallen in numbers by more than 80% in recent years.

Bumblebees are vital in pollinating crops like apples and raspberries, experts say, and as native insects they are important parts of their ecosystems. Besides climate change, other threats they face include pesticide use, and our changing landscapes and countryside - as the diverse wildflower meadows they depend on turn into apartment blocks or intensive farms.