Red-tailed bumblebee. Photo: Jeremy T. Kerr/PA WireRed-tailed bumblebee. Photo: Jeremy T. Kerr/PA Wire

Global warming could silence the summer buzz of the bumblebee forever unless urgent action is taken to save the insects, scientists have warned.

Evidence shows that warmer temperatures are having a devastating effect on the heavyweight bees that play a vital role as wild pollinators.

Unlike other insects, such as butterflies, they are not migrating further north in search of cooler places to live, say experts.

Instead, their range areas are being squeezed and their populations are dwindling.

The study of 67 species shows that over the past 110 years bumblebees have lost about 295 kilometres from the southern edge of their living space in Europe and North America.

Southern bee populations are disappearing as conditions become too warm for them, but there is no corresponding shift northwards. The northern boundary of the bees’ territory is not moving, the study shows.

The scariest parts of the work is just realising how quickly the situation is changing

A strong correlation was found between what was happening to the bees and climate change.

Lead scientist Jeremy Kerr, from the University of Ottawa in Canada, said: “Global warming has trapped bumblebees in a kind of climate vice.

“The result is dramatic losses of bumblebee species from the hottest areas across two of the continents.

“For species that evolved under cool conditions, like bumblebees, global warming might be the kind of threat that causes many of them to disappear for good.”

It may be necessary to help bumblebees establish new colonies further north by physically moving them, say the researchers.

So called ‘assisted migration’ is controversial among conservationists but gaining support in a warming world.

Bumblebees may be unusually vulnerable to climate change because, unlike many other insects with tropical origins, they evolved in the ‘Palearctic’ ecozone that encompasses Europe, northern Asia and northern Africa.

For this reason they may not be so able to adapt to warmer temperatures, according to the experts whose findings are reported in the journal Science.

British co-author Sheila Colla, from the University of York, said bumblebee species that once were quite common were now becoming rare. A third of North American species were in decline and some populations had crashed by more than 90 per cent.

One, the rusty-patched bumblebee, was the fourth most common species in southern Ontario, Canada, in the 1970s and 1980s. Colla said she had only seen two of the insects in the last 10 years despite extensive searching throughout their habitat range in both Canada and the US.

She added: “One of the scariest parts of the work that I’ve done is just realising how quickly the situation is changing. The bumblebees that are in decline were doing fine 50 years ago. We’re talking about large changes in community composition of essential pollinators over just a few decades.”

The scientists looked at factors besides climate change that might have had an impact on the bees, including land use and pesticides.

None were found to be relevant to the bumblebee range losses.

“Bumblebee disappearances from warm, southern areas are just as likely when there is no pesticide use and little agriculture,” said Kerr. “But we know that increasingly frequent weather extremes, like heat waves, can hit bumblebee species hard, and climate change poses threats that are already felt.”

The study found that while bumblebees were not extending the northern end of their range, some were heading for the hills and cooler, higher altitudes.

Expert Stuart Roberts, from the University of Reading, who was one of the study authors, said: “Climate change is altering habitats quickly, but the dispersal range of most bumblebees is not great.

“Bumblebees might be able to live in climatically suitable habitats further north, but many of them just can’t get there.

“Large swathes of land in some parts have become so degraded and inhospitable that bees can’t travel across them to find the more suitable homes that are opening up further north. Other natural barriers to movement, such as mountain ranges or seas, have the same effect.

“In addition, bees which rely on mountainous habitats are moving higher up as the lower reaches of mountains warm up to uncomfortable levels. If they can now only find the habitat they need at the very tops of mountains, they will be left stranded with nowhere else to go as the climate warms further.”

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