In Photos: The World's Most Efficient Pollinators

Bumblebees evolved about 35 million years ago in cooler climates. The buzzing insects are the superstars of the pollinator world, working harder, longer and on a broader variety of species than other bee species. Here, a red-bellied bumblebee cozies up to a lupine. Its body is covered in pollen, which it will spread to other flowers, thereby helping the lupine plant complete its reproductive cycle. (Credit: Jeremy T. Kerr.)

Shrinking range

In the new study, researchers found that bumblebee populations have disappeared from its historic southern edges but have not colonized northern areas that have warmed. The trend tracked with human-caused climate change, but was not caused by exposure to pesticides or land-use practices. (Credit: Ann Sanderson, Sheila Coila.)

Collapsing population

The reason for the decline in hotter areas is clear: the bumblebees did not evolve to tolerate extreme heat, and simply die off during hot weather. Here, a red-tailed bumblebee dines on garden plants in the United Kingdom. (Credit: Jeremy T. Kerr.)

Moving on up

The study also found that bees are moving up mountainsides, residing at higher altitudes than they previously had. Once again, global warming may be the culprit here, as temperatures drop as elevation increases.  (Credit: Ann Sanderson, Sheila Coila.)

Diverse group

Here, a red-tailed bumblebee from Denmark dips its nose into a flower. Bumblebees aren't the only pollinators in the insect world; about 20,000 other bee species also play a critical role. But many of those bees pollinate just two or three plants, or are active for just a few weeks of the growing season, researchers said. (Credit: Jeremy T. Kerr.)

Nectar sipping

Here, a buff-tailed bumblebee is sipping nectar from a catmint flower in Nottingham, United Kingdom. The buff-tailed bumblebee will then move on to other flowers, spreading the plants pollen as it goes. (Credit: Jeremy T. Kerr.)

Resilient holdouts

The buff-tailed bumblebes, like the one shown here, is one species of bee that is doing just fine despite global warming. The hardy, weedy species, called the dandelion of the bumblebee world, seems to be able to adapt to new areas fairly quickly because it lives in large colonies. That, in turn, may help the bees quickly establish new populations in new habitats, researchers speculate. (Credit: Jeremy T. Kerr.)