UK bumblebee populations experienced significant declines in 2022, a year marked by multiple heatwaves and record-breaking temperatures, according to data from the BeeWalk scheme. The intense heat poses a dual threat to these insects, compromising their ability to regulate body temperature and sustain foraging activities.
Bumblebees native to the UK are well-adapted to the country's historically cooler climate. Their thick, furry bodies and powerful flight muscles, which generate heat, are beneficial in colder conditions. However, during heatwaves, these adaptations become detrimental. The furry coats make it difficult for them to dissipate heat, and their muscles can overheat, leading to a critical rise in internal body temperature. Scientists warn that when air temperatures consistently reach between 28C and 32C, bumblebees can struggle to fly without overheating. If flight becomes impossible, foraging ceases.
"They actually cook themselves from the inside out," explained Dr. Richard Comont, the conservation trust's science manager. "Once their internal body temperature is much above 40C, they literally start dying, they start keeling over."
Data from 2022 illustrates the severity of the impact. During the three official summer heatwaves, with temperatures peaking at 40.3C, common bumblebee species saw substantial population drops. The red-tailed, buff-tailed, and common carder bumblebees recorded population numbers well below their typical peaks, declining by 20%, 25%, and 35% respectively. These numbers continued to fall into the autumn as colonies struggled to survive.
The effects of the heatwaves were not confined to a single summer. BeeWalk data indicated that the number of queen bumblebees remained below average in March, April, and May of 2023, suggesting a lingering impact on reproductive success and colony establishment following the extreme weather events of the previous year.