A novel fungus may be devastating bats in the northeastern U.S. In the past two years several species have displayed unusual behavior such as flying during the winter when they should be hibernating. Census counts in Connecticut, Massachusetts, New York and Vermont have revealed that populations have thinned by at least 75 percent.

A clue has been a white, powdery organism on the muzzles, ears and wings of the dead and dying bats, creating what is called white nose syndrome. In a report published online October 30 in Science, microbiologist David S. Blehert of the U.S. Geological Survey and his colleagues identify the white stuff as a type of Geomyces fungus, one of a group of ubiquitous organisms that reproduce at refrigerator temperatures of four degrees Celsius—and a typical bat-cave reading.

Researchers remain unaware of the source of the fungus or even its exact role in the deaths. The pathogen may attack torpid bats and keep them awake, so that the mammals burn too much of their stored fat—most victims have been rail-thin, and some have been found outside their caves, perhaps after a futile attempt to catch insects to eat in winter. Or the fungus may simply be an opportunistic infection following a more profound sickness sweeping the animals. The researchers plan to study the effect of this fungus on healthy bats in the lab this winter.