Bumblebee numbers in Great Britain declined by almost a quarter in 2024 compared with the 2010-23 average, making it the worst year for the genus Bombus since records began, according to the latest “BeeWalk” report.
BeeWalk, run by the Bumblebee Conservation Trust, is an annual standardized monitoring program, in which volunteers and partner organizations record the abundance of different bumblebee species across Great Britain between March and October.
In 2024, BeeWalk records showed that only about nine bumblebees on average were seen per kilometer (0.6 miles) walked as opposed to some 12 in 2023 and a peak of around 14 in 2015.
The report cited wet and cold weather from April to June as one of the factors impacting many iconic British bumblebee species, which are important pollinators of crops and wildflowers. The late spring to early summer period is critical for the colony establishment stage, when queen bumblebees create new nests.
Richard Comont, Bumblebee Conservation Trust’s science manager, told Mongabay by email that queens at this stage act as “single parents” that forage to feed the whole nest.
However, in cold, wet weather, many flowers close, fall off or don’t produce as much nectar or pollen, Comont said. Flying in rain is also much harder for the queen and takes up more energy, while the brood needs more incubation so the larvae don’t die of cold, he added.
“When there is cold, wet weather while the queen is a single parent to the developing brood, it increases the chance of nests failing in the same way that it does for birds,” Comont said.
While weather has a role to play, it’s difficult to pinpoint climate change as a main driver or “smoking gun” of bumblebee population trends in the past 15 years because of its complexity, Comont said. “But it’s pretty clear that the effects of climate change — increased flooding, more & hotter heatwaves, more unstable weather patterns, etc — will be increasing the pressure on bumblebee populations.”
Although overall bumblebee numbers were lower in 2024, the report noted the situation was nuanced for each bumblebee species, depending on the season.
Species that recorded the biggest decline in England, Scotland and Wales during June or July, when their colony size should be at their peak, were the white-tailed (Bombus lucorum s.l.) and red-tailed (B. lapidarius) bumblebees, with declines of 60% and 74%, respectively.
For late-peaking species in August, trends were mixed: The heath bumblebee (B. jonellus) saw a 63% increase but both the common carder bumblebee (B. pascuorum) and the moss carder bumblebee (B. muscorum) recorded declines.
The rarest bumblebee in England and Wales, the shrill carder bumblebee (B. sylvarum), was up by 74%, although the species was not recorded in two of its five remaining populations.
Comont said it’s important to improve the resilience of existing populations through ensuring enough nesting sites and flowering plants.
Banner image of a bumblebee in the U.K. by Flappy Pigeon via Wikimedia Commons (CC BY-SA 4.0).
