Flitting from flower to flower, the world’s many bumblebee species (Bombus) are some of our most important pollinators. These fuzzy yellow insects will deploy their signature buzz to literally vibrate the pollen off plants. By supporting countless ecosystems, bumblebees bolster biodiversity, anchor food chains and help ensure humans’ agricultural security.

When bumblebees are in trouble, so, too is the rest of the globe—and we’ve apparently arrived at that sobering reality, according to a new study published last week in Science.

A new analysis of a massive, international dataset has found that, in the span of just a few decades, the number of places populated by bumblebees have declined by 46 percent in North America and by 17 percent across Europe. Climate change appears to be a major culprit, driving temperature spikes and extreme heat waves that—combined with pesticide use, disease, and habitat loss—may threaten the insects with imminent extinction.

“These declines are linked to species being pushed beyond temperatures they haven’t previously had to tolerate,” University of Ottawa biologist and study author Peter Soroye tells Douglas Main at National Geographic.

While bumblebees comprise just a fraction of the world’s insect pollinators, they’ve carved out a substantial niche for themselves in the agricultural sector, aiding the fertilization of crops like tomatoes, blueberries and cranberries. In total, some 250-plus species of bumblebee roam the Earth.

But the fuzzy buzzers are fragile, too. Decked out with thick coats of yellow hair and wings that generate heat when the bugs are aloft, bumblebees are best suited to cooler weather. When temperatures skyrocket outside their typical range, the bees are quick to overheat.

“They’re effectively sewn into their winter underwear, as it were, so it’s a challenge for them to adjust behaviorally or physiologically to warming temperatures,” explains May Berenbaum, an entomologist at the University of Illinois at Urbana-Champaign who wasn’t involved in the study, in an interview with Chris Mooney at the Washington Post.

Compounding the issue is the sensitivity of plants, which can wither in high heat, starving the bees of a crucial food source. The past two decades have been the hottest on record—and the bees have certainly felt the heat.

Soroye and his colleagues analyzed observations of 66 bumblebee species over the past century, comparing the period spanning 1901 to 1974 to another between 2000 and 2014. Of the regions in North America that bumblebees once called home, nearly half no longer housed the insects by the start of the 21st century. These geographic changes could mean the insects have either migrated away or died; either way, the region is left bumblebee-free.

As Soroye tells Kendra Pierre-Louis and Nadja Popvich at the New York Times, the bees’ disappearance tracked specifically with regions that were experiencing more temperature extremes, rather than only increases in average temperatures.

Heather Hines, an entomologist at Pennsylvania State University who wasn’t involved in the study, stresses that while climate change “can explain declines to a large degree,” the study’s findings shouldn’t diminish the focus on other factors known to imperil bumblebees, National Geographic reports. Pesticides, habitat destruction, invasive species and deadly pathogens contribute as well and will need to be addressed as pressing issues if the world’s bees are to be saved, explains Jamie Strange, an entomologist at Ohio State University who wasn’t involved in the story, in an interview with National Geographic.

The study’s findings, which centered on North America and Europe, will also need to be replicated in other parts of the world to keep perspectives from being too “Western-centric,” as bee expert Sydney Cameron of the University of Illinois at Urbana-Champaign, who was not involved in the study, tells the Washington Post.

In the meantime, a few of the results may offer hope as well: The analysis also pinpointed places where bee populations had remained stable, or even increased. “We can go to these bright spots where things are going well,” Soroye tells the New York Times. “We can see what it is about those regions and those areas that’s allowing species to persist under climate change.”