Pseudogymnoascus destructans was first recorded in a cave near Albany, New York, in the winter of 2006 to 2007. It thrives between roughly 4 and 15 degrees Celsius, the range that hibernating bats seek out, and colonises exposed skin on the muzzle, ears and wing membranes.
The mechanism is metabolic rather than directly toxic. Infected bats rouse from torpor far more often than healthy ones. Each arousal costs a disproportionate share of a fat budget calculated to the gram, and infected animals leave the hibernaculum early, in midwinter, to search for insects that are not there. Damage to the wing membrane also disrupts water balance.
Declines at affected northeastern hibernacula have exceeded 90 per cent for Myotis lucifugus, and the species has been listed as Endangered. What is not settled is whether the surviving remnant carries heritable resistance or has simply shifted to cooler, drier roosts where the fungus grows less well.