Vampire bats (Desmodontinae) are a marvel of evolution. They represent one of the fastest evolutionary divergences within the vertebrates. Evolved from an insectivorous ancestor some 22 million years ago, the route to ‘vampirism’ was achieved within a mere 5 million years. Fraught with more risks than one might think, the complete, all-inclusive diet afforded by blood-meal provided an irresistible evolutionary incentive. A one-stop, fly-by meal, rich in protein and nutrients. Only getting by without getting caught is harder than one might think, and the unique suite of physiological adaptations, stranger than one can imagine.
Desmodus rotundus, the common vampire bat, is found in colonies with hundreds of individuals mainly females with their offspring; typically found in caves but in the Amazon rainforest is found in hollow trees. Photo by CC BY-SA 3.0
Of course, for a creature that weighs under 100 grams, simply approaching a host entails a perilous undertaking requiring the utmost stealth. Flight can be noisy or create drafts that can wake sleeping prey. Thus, these bats have regained the ability to walk, hop or even run (up to 2 meters/sec) using the combination of powerful legs and wings, enabling them to follow, or approach sleeping prey without alerting them to their presence and to quickly maneuver out of the way of a potentially fatal blow.
Vampire bats…
Once they have reached their intended target, they locate ‘hot spots’ – capillary-dense, thin-skinned areas like the feet which are ideal for feeding. Vampire bats are the only mammals known to be able to detect infrared radiation – heat, and they do so by lowering the activation threshold of a cluster of specialized heat-sensitive neurons – the trigeminal ganglia – present in ‘leaf pits’ surrounding the nose. Once they have selected a spot, they must pierce the skin or tough hide, sometimes first shearing the site to clear it of hair that might otherwise interfere with feeding and all without alerting the host to their presence. They are able to do this through yet another specialized adaptation – razor-sharp incisors kept perpetually sharp through the lack of tooth enamel. Because these incisors are so sharp, less pressure needs to be exerted to break the skin, reducing the chances of waking the host.
Now that the vampire is ready to feed, it uses yet another innovation, a specially grooved tongue. Blood is held within two channels on the underside of the tongue through capillary forces and then drawn up through muscle contraction in a kind of ‘tongue-pump’, all whilst saliva, containing an anticoagulant, Draculin, (a molecule of interest for the treatment of stroke victims) trickles down the topside of the tongue to keep the blood flowing in one of the most morbidly fascinating adaptations I’ve had the pleasure of learning about!
