Bees increasingly unable to fly as climate crisis raises frequency of extreme weather

Increasing rate and severity of weather including cold snaps and soaring temperatures could impact insect pollination, scientists warn

While rising average global temperatures could help some species of bee living in northern latitudes fly better, increasingly extreme weather events could “push them past their limits”, scientists have warned.

The research team, from Imperial College London, measured the relationship between bumblebee flight performance and surrounding temperature.

They measured both the bees’ motivation to fly, and their flight endurance, and found performance rose rapidly from the lower tested limit of 12C and peaked between 25-27C.

Beyond this, however, they found performance started to decline.

The results are concerning as temperatures across parts of Europe, the US, Canada and even Siberia have soared well above this upper limit in recent weeks amid extreme weather events.

The team said their results show that while bumblebees found in more northern latitudes may see benefits to flight performance under future climate warming, populations in southern latitudes, where temperatures above 27C are more readily exceeded, may be adversely affected.

Separate research has warned that heatwaves are becoming hotter and more frequent due to the impacts of the worsening climate crisis.

First author Daniel Kenna from Imperial College London said: “Climate change is often thought of as being negative for bumblebee species, but depending on where in the world they are, our work suggests it is possible bumblebees will see benefits to aspects of an important behaviour.

“However, more extreme weather events, such as cold snaps and the unprecedented heatwaves experienced in recent years, could consistently push temperatures beyond the comfortable flight range for certain species of bumblebees.”

He added: “These risks are particularly pertinent for ‘fixed colony’ pollinators like bumblebees, which cannot shift their position within a season if conditions become unfavourable, and potentially provide a further explanation as to why losses have been observed at species’ southern range limits.”

Temperature is a very important factor in determining how well many insects fly. Too cold and the bees’ flight muscles can’t function fast enough to support flight. Too warm and they could overheat.

To measure how the quality of the bees’ flight is impacted by air temperature, the team temporarily attached bumblebees to “flight mills”, which allowed them to fly in circles like a carousel, capturing the distance and speed of flight.

They tested bees ranging in body size at temperatures from 12-30C and used their results to construct a thermal performance curve.

The curve predicts that while bumblebees can fly around 3km (1.8 miles) at their thermal optimum, this average flight distance could be reduced to under 1km when temperatures rise to 35C, and could plummet to just a few hundred metres at a chilly 10C.

At temperatures of 15C and below, the team said their bees weren’t motivated to fly and frequently would not fly more than 100 metres. Moreover, it was only the bigger sized bees that successfully flew at these low temperatures, suggesting smaller individuals dislike cold days but may benefit more from climate warming.

Lead researcher Dr Richard Gill, from Imperial, said: “While we still need to understand how these findings translate to factors like foraging return to colonies and pollination provision, as well as applicability to other bumblebee species, the results can help us understand how smaller versus larger flying insects will respond to future climate change.”

He added: “It’s not just pollination: how different flying insects respond to warming temperatures could also affect the spread of insect-borne diseases and agricultural pest outbreaks that threaten food systems. Applying our experimental setup and findings to other species can help us to understand future insect trends important for managing service delivery or pest control methods.”

The research is published in the journal Functional Ecology.