In the past five years, reports of staggering insect declines have stoked anxiety and debate concerning the fate of the “little things that run the world,” as the late biologist E. O. Wilson once called them. As for the how and why of these declines, the prime culprits are habitat destruction, rampant use of pesticides, and climate change.

But new research published March 30 in Biology Letters adds an unexpected suspect, at least for a large swath of North America: the earthworm. The study looked at 60 plots in an aspen and poplar forest in Alberta, Canada, and found that as the numbers of earthworms wriggling in the soil