Climate change is threatening the habitats of bumblebees, a critical pollinating species that is needed to preserve ecosystems, researchers said Thursday. A Canadian-led team of scientists found that bumblebees are suffering from drastically reduced populations.

"The rates of loss are very rapid and are nearly the same across continents," Jeremy Kerr, an ecologist at the University of Ottawa and the study's lead author, said at a press conference on Thursday, CBC reported. Bees are considered to be a "keystone species" necessary for the health of ecosystems they inhabit. The researchers warned that their disappearance would have a knock-on effect on other species.

The insects are also critical for agriculture, with farmers relying on them in spring, summer and autumn to pollinate crops. Their numbers have been falling precipitously in the past two decades, with many species disappearing entirely.

The researchers found that bumblebees were squeezed out of about 5.6 miles a year since 1975, and that they were extinct in almost 180 miles in the southern part of their ranges. The southern species were moving upward, increasing their elevation by almost 1,000 feet over the same period, they said. The results of their research were published Friday in the journal Science.

The researchers thought that the bumblebees would migrate north with time, as other insect species like butterflies have done. Kerr said he was "shocked" to find out that this was not the case. "Our results show very clearly that that generally is not what they're doing at all, they're not expanding their range, unlike butterflies," he said, according to the Guardian.

The scientists examined around 423,000 records for 67 bumblebee species across Europe and North America, dating back 110 years. They mapped changes in the bees' territories and noted the coldest and warmest places that they inhabited. Using statistical methods, they isolated the effect of climate change on their population and range shifts.

By isolating the effects of various factors, they found that climate change had a bigger impact in shrinking their range than pesticides or land cover. They believe that the bees' retreat to higher elevations indicates that they evolved to favor colder climes than other insects, making them especially sensitive to temperature increases.

However, they could not account for their failure to move north. "There is a mystery here that we need to solve quickly," Kerr reportedly said. He hopes his research would help add urgency to the immediacy of climate change. "Bees capture the public's imagination, and maybe that will help governments to act," he said.