UK heatwaves threaten bumblebees as population declines each year due to intense heat

Britain's bumblebee populations could experience dramatic declines as heatwaves grow in both frequency and severity, fresh analysis from the Bumblebee Conservation Trust has warned.

The research, based on the Trust's long-established BeeWalk national monitoring programme, reveals that numbers fell markedly following the unprecedented temperatures recorded in 2022.

The findings arrive as the country recovers from its third heatwave in three months, with conditions reaching levels at which bumblebees risk overheating during flight.

Beyond being among the most cherished features of a British summer, bumblebees serve as essential pollinators, underpinning the survival of wildflowers and contributing to the production of key food crops.

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British bumblebee species have evolved for the UK's traditionally cool climate, possessing thick, furry bodies designed to retain warmth and muscular flight systems that generate heat during activity.

During scorching conditions, however, those same adaptations become a liability, their powerful muscles produce excess heat while their dense coats and rotund frames prevent effective cooling.

Dr Richard Comont, the Trust's science manager, explains that air temperatures between 28C and 32C can leave UK bumblebees unable to fly without overheating, cutting them off from foraging.

Dr Comont said: "They actually cook themselves from the inside out. Once their internal body temperature is much above 40C, they literally start dying, they start keeling over."

According to BeeWalk data, the 2022 season - during which the UK endured three official summer heatwaves and a record temperature of 40.3C - saw significant population falls.

Red-tailed bumblebees peaked 20 per cent below typical levels, buff-tailed species were down 25%, and common carder bumblebees dropped by 35 per cent, with numbers sliding further into autumn as colonies faltered.

The damage extended well beyond that single summer, with queen counts remaining below average throughout March, April and May 2023.

Drought compounds the crisis. Colonies rely on workers delivering a constant supply of nectar and pollen, but parched flowering plants yield less of both.

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Dr Paul Williams, a bumblebee specialist at the Natural History Museum, describes foraging as an energy equation.

He said bees need to "make a profit" from each trip, and cannot squander effort visiting dried-out blooms.

When food becomes scarce, larvae grow more slowly, colonies weaken, and fewer new queens emerge to establish populations the following year.

Conservationists argue that establishing flower-rich habitats offers the most effective defence, ensuring bumblebees can locate sustenance even as conditions worsen.

Dr Sarah Beynon, an entomologist who manages her west Wales farm for both agriculture and wildlife, has transformed barren land through meadows, hedgerows and late-flowering crops.

She said: "Your flowerpot is a service station. It's somewhere to rest, refuel and carry on."

Dr Comont recommends adding ponds and dense shrubs.

Plants near water produce more moisture-rich nectar, crucial since bumblebees obtain most liquid from nectar rather than drinking directly, while shaded corridors let them navigate between flowers through cooler air.

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