Except in the insectivorous forms, the soft impulses emitted by the members of this family are a complex and changing mixture of high frequencies of short duration. Some species aid in seed dissemination, and those that seek nectar, pollen, or insects from flowers pollinate the flowers. The scientific names of certain genera suggest that they drink blood, but their food habits are actually much like those of most other phyllostomids. The Desmodontinae are the true vampires, feeding, so far as is known, only on fresh blood. Their method is to alight on or near the prospective victim and walk or climb onto it.
Vampires attack in areas without hair or feathers or where the hair is scant.
These include the naked skin around the anus and vagina, the ears and neck of cattle, and the wattles and combs of chickens. When a suitable area is found, the bat makes a quick shallow bite with its very sharp teeth that cuts away a small thin piece of skin. This operation is practically painless and usually does not disturb the sleeping or quiet animal or human being. The bats do not bite deeply or struggle with a victim. The tongue of the bat is then applied to the wound.