This idea likely arises from the tropics where true vampire bats feed off blood from small wounds they inflict in cattle. It is the humans that have made bats the victims. Often developers building houses will find a colony of bats, and wipe out the entire group. Insects often carry traces of insecticides that we spray on crops and gardens. When the bat eats the insects, the pesticides collect, the bat's body cannot rid itself of the chemicals.
Bats can die if the levels reach too high.
Three species of bats are now on the endangered list. The insect-eating bats of this area cause no harm, and decrease the insect population. For those who still hesitate to appreciate the little bats that eat insects and occasionally make a wrong turn and explore our houses, consider the larger megabat of Africa and India. This page is best viewed when using Netscape 2.0.