Vampire bats are a certain species of bat that are known to have preyed on certain animals by biting into them & lamping or sucking blood out of them (e.x.: cows, livestock, humans). There are different subspecies of vampire bats, one in particular evolved to prey on human blood, this subspecies only exists on the planet of Chiron.
Vampire bats that live on Chiron had existed for thousands of years, evolving from wingless rodents into furry bats with leather wings & killer fangs. Unlike other vampire bats, they were trained by certain evil people to hunt their enemys & these bats evolved into the present-day subspecies that can be trained to hurt certain people & prey on their blood & flesh.
A vampire bat's most fatal weapon is a technique dubbed the Bat's Kiss. A bat will bite into the victim & release a toxic substance that will cause unconsciousness. The bat will then clamp it's jaws onto & over the wound & it would start to suck out the blood. A vampire bat performing the Bat's Kiss can lower the blood levels to the point that the victim will not have enough to survive. If the victim was swarmed by bats, several of them could attempt a "Group Kiss", where they'd attack in different places & "Kiss" the wounds & suck out the blood, killing the victim in minutes.
During the second attempt to destroy the Pure Ones in the Battle of the St. Aegolius Academy for Orphans, Bart Sampson, Lyze of Kiel, Lowak of Iks & Brian of Yore all attempted a dangerous flight towards the St. Aegolius Academy throne room. Somewhere between the pillar they lifted off from & the throne room, they were surrounded by a horde of vampire bats. A few bats began to encircle the four & attacked. Bart Sampson attempted to swat it away with his wings & missed. The bat then flew straight around & bit him right in the leg, forcing the venom into him. Bart lost consciousness & plummeted as bats began to feast on him, biting him & attempting the Kiss. Lowak of Iks removed the bats from Bart & was surprised to find that one had almost killed him by lodging itself in his mouth & sucking his tongue.