The document discusses white-nose syndrome, a fungal disease that has led to the extinction of many bat species. It is caused by a white fungus, Geomyces destructans, that grows on bats' skin during hibernation and causes them to use up their fat reserves and die before spring. The disease kills bats by depleting their energy, compromising their immune systems, damaging their wings, and altering their behavior. Its impact is significant because bats control insect populations and help ecosystems and agriculture.