There's a newly-determined "major factor" in declining bumblebee populations – and it's attacking their nests.

New research from the University of Guelph said on Friday that temperatures are becoming too hot for bumblebees, threatening their role as plant pollinators and the food supply for humans and other animals.

The global bumblebee population has declined since the 1950s, sparking speculation on the causes – researchers have suggested everything from pesticides to habitat loss. Because bumblebees are vulnerable to temperature swings, some have proposed another culprit: climate change.