Scientists say wild bumblebee species are being squeezed into extinction by climate change in North America and Europe — so much so that some of them might need help from us humans to find safe havens.
Their conclusion, published in this week's issue of the journal Science, is based on an analysis of more than 423,000 archived observations of 67 bee species, going back to 1901.
The scientists expected to find that the species have moved northward in response to rising temperatures, as other species ranging from flowers to foxes have done.
That's not what they found. Yes, the bumblebee species dwindled or disappeared in warmer southern climes, retreating an average of about 190 miles (300 kilometers). And in mountainous regions the bees moved up to higher elevations — about 1,000 feet (300 meters) higher, on average. But they didn't move into cooler, higher-latitude regions.
For some reason, bumblebees are being caught in a "climate vise," said University of Ottawa biologist Jeremy Kerr, the lead author of the Science study.
Kerr and his colleagues tried to account for other factors that have been cited as bad for bees, ranging from neonicotinoids and other pesticides to changes in land use — but they said those factors don't explain the losses in the range of the species.
The scientists emphasized that the scenario for wild bumblebees is different from the problems faced by European honeybees.
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The concern about honeybees focuses on colony collapse disorder, which has been linked to a host of factors including pathogens, pesticides and diversity loss. But the concern about bumblebees is just as serious, said study co-author Leif Richardson, a bee researcher from the University of Vermont.
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Richardson pointed out that bumblebees play a key role in pollinating crops ranging from apples and blueberries to soybeans. "If we see declines in the diversity or abundance of bumblebees, we should expect to see lower crop yields, higher food costs, and perhaps lower food diversity," he told NBC News.
Why bumblebees are bummed
The researchers suggested that bumblebees aren't as capable of coping with warmer temperatures as, say, butterflies, because bumblebees evolved in temperate regions of the world rather than tropical regions.
"You imagine a car that starts running out of coolant and starts blowing steam out the front of the hood. That’s kind of like an analogy for what bumblebee species do when it gets too hot," Kerr told reporters.
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So why aren't bumblebee species pushing farther northward into Canada, or showing up in more northerly regions of Europe? The reasons for that aren't fully clear: It may be that the plants on which the bumblebee species feed are lacking, Or it may be that the bee colonies have to be of a certain size to take root in new regions. Kerr noted that bumblebee species with larger colony sizes seemed to handle moving into new areas better.
About a third to a quarter of the bumblebee species are in decline, but some species "seem to be expanding their range," said York University's Sheila Colla, another co-author of the study. These include the common Eastern bumblebee in the United States — as well as the buff-tailed bumblebee in Europe, which Kerr called the "dandelion of the bumblebee world."
What is to be done?
The researchers said regular folks could help out the bumblebees by planting bee-friendly crops in their gardens and backyards — native wildflowers, bee balm and milkweed, for example, or even raspberries. Another way to boost the bees is to participate in BumbleBeeWatch.org, a citizen science project that keeps track of bee sightings in North America.
The study touches on the strategy of "assisted migration" — that is, transporting bumblebee colonies to cooler refuges. Kerr said conservation groups and government agencies will have to have a "thoughtful and quick conversation" about when and how to use such a strategy.
"We're playing with fire, and we are now going to begin paying some of those consequences," Kerr said. "If we’re interested in conserving species like bumblebees for the future, it is possible that we will need to intervene in a significant and extensive way to help them adapt."
Related: Honeybee Diseases May Spread to Bumblebees
Richardson said assisted migration should be employed with extreme caution.
"We may have to do that, but if recent experience serves, there are perils that we engage in when we start moving species around," he told NBC News. Richardson pointed to the example of the European buff-tailed bumblebee, which was exported to Chile and Argentina to boost pollination but is now considered an extremely invasive species.
He said it would do no good to try saving species after species without doing something about our own species' greenhouse-gas emissions and the effect on global climate.
"To address the root cause of what's happening to the bumblebees, the answer is clear," Richardson said. "And it's as intractable as ever."
In addition to Kerr, Colla and Richardson, the authors of "Climate Change Impacts on Bumblebees Converge Across Continents" include Alana Pindar, Paul Galpern, Laurence Packer, Simon Potts, Stuart Roberts, Pierre Rasmont, Oliver Schweiger, David Wagner, Lawrence Gall, Derek Sikes and Alberto Pantoja.