It’s official: A systematic test with initially healthy little brown bats shows that a fungus is the primary cause of white-nose syndrome. The lethal disease has devastated bats hibernating in 16 U.S. states and four Canadian provinces (infected bat pictured). In addition, tests show that the fungus, Geomyces destructans, can spread by contact in shared hibernation spots, David Blehert of the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis., and his colleagues report online October 26 in Nature. The causal fungus is widespread in Europe but doesn’t cause big dieoffs there, possibly because the bats had a long time to develop ways to cope. Pinpointing the exact cause of the syndrome will help wildlife experts focus research on what to do about the scourge.