Bumbling Toward Extinction

Global warming is forcing many species to migrate away from the poles. Butterflies, several bird species, marine invertebrates, and even trees (not the most mobile creatures) are shifting their ranges, trying to stick to safe temperatures. A 2011 study found that the average species is moving to higher latitudes at a rate of more than 10 miles per decade.

Ecologists are most concerned about creatures that could become stranded by climate change—those that have reached the edges of a continent or the top of a mountain and can go no farther. But what about species that seem capable of moving but don’t? A new study in Science reveals that bumblebees are one such species, stubbornly refusing to acknowledge climate change. Call them the Jim Inhofes of the animal kingdom.

An international team of ecologists and biologists analyzed more than 400,000 mentions of bumblebees in academic and scientific literature with reference to location between 1901 and 2010. These references were used to determine changes in the creatures’ habitat. (You can undertake your own sleuthing using one of the authors’ open-source databases.) The researchers found that bumblebees, unlike most other observed species, aren’t shifting into higher latitudes in North America and Europe. And they are suffering for their intransigence.

The bumblebee’s habitable range is shrinking rapidly. Increasing temperatures have closed off the southern parts of the insect's range, in many areas forcing the southernmost bees northward by more than 185 miles. Some of the bees compensated for the increasing heat by moving into higher elevations at the same latitudes, but there simply isn’t enough mountain landscape to make this compensatory move sustainable over the long term. Bumblebees are in trouble.

The surprising thing about this study is the source of the trouble. Most people thought chemicals were the primary threat to bees—insecticides like neonicotinoids that farmers spray on and around their fields. Those are still a problem, but they do not explain the bumblebee’s shrinking range.

“Picture a vice. Now picture the bumblebee habitat in the middle of the vice," says Jeremy Kerr, the University of Ottawa ecologist who led the study. "As the climate warms, bumblebee species are being crushed as the ‘climate vice’ compresses their geographical ranges. The result is widespread, rapid declines of pollinators across continents, effects that are not due to pesticide use or habitat loss. It looks like it's just too hot."

You probably already know that bumblebees are important pollinators, but bear with me while I tell you just how important they are. Using their tongues, called proboscides, bumblebees lick the nectar out of flowers. Since the 49 species of North American bumblebee have tongues of varying length, they can pollinate flowers of many shapes and sizes. They’re also clever little devils: The ones with the short tongues have figured out how to gnaw through the backs of flowers to get at the nectar, in a process known as “nectar robbing.”

You know that pesky buzzing sound bees make? It’s a crucial pollination tool as well. By rapidly vibrating their wing muscles, the bees create a wave of sound that shakes pollen grains out of plants (such as tomatoes) whose pollen is very difficult for other pollinators to access.

The shrinking range may already have had irreparable consequences. Within the past decade, two species of bumblebee with already small ranges have gone extinct. It’s not clear that climate change was solely responsible—disease and destruction of their habitat by humans probably contributed—but it’s likely to have played a role.

It’s not yet clear why bumblebees are failing to head toward the poles like so many other species. That’s a great topic for the next set of ecologists to address. In the meantime, this study is yet another reminder that we’re thoughtlessly risking the existence of some extremely important farmhands.