Crimson Forest: A Vampire Tale

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!

But we’re not done yet! Like the safe-cracker who pulls out tool after tool to pull off a heist, the vampire bat isn’t finished.

A vampire bat skeleton, showing distinctive incisors and canines. Photo by Mokele

Drinking between a third and half of their body weight in a single feeding, this sudden weight gain could imperil flight or even ground them if not for their ultra-efficient kidneys and long, thin, and muscular bladder. This combination allows them to rapidly process the blood plasma (which is 90% water), absorbing the protein from the blood and excreting the excess fluid in the form of urine, all while still feeding.

Whereas ingesting a huge volume of liquids represents a physical challenge, the ingestion of large amounts of iron in the form of heme from hemoglobin (the iron-based molecule used to bind and transport oxygen) and nitrogenous proteins forms a chemical challenge, which can lead to toxicity. Laboratory studies have shown that macrophages (white blood cells with important immune functions), have been co-opted to help remove excess iron, whilst an as yet to be understood process appears to afford some form of protection from chronically high blood-nitrogen levels (azotemia) which would be otherwise debilitating and could represent yet another medically valuable avenue, this time for renal disease victims.

Fed and satisfied, the bat returns to its communal roost where it may engage in one of the few known cases of reciprocal altruism, a hotly debated behavior amongst biologists, whereby unrelated individuals share resources at a significant cost to the donor. Due to their high metabolic rates, bats must feed every 48 hours or else they will starve. To hedge against this starvation, bats will share with unsuccessful roost-mates, regurgitating blood with the expectation that their roost-mates will reciprocate in the future.

And so, while the vampire bat has earned a fearful reputation inspiring an entire horror genre, through insight and understanding of its complicated biology, this creature’s astounding natural history is less awful and more awe-inspiring and provides a story we can all really sink our teeth into.

So, if you are asking where do vampire bats live, you can find some in the Amazon Rainforest of Peru.

• Go on a hike in the rainforest with a trained guide: Bats are anywhere in the rainforest. However, to see a bat, hang out with a guide on a night walk around one of our trails.

• Sign up for a Free Trial of the Wired Amazon: even if Amazon Travel is not in your short-term plans you can connect with Amazon wildlife. Sign-up for your free trial of the Wired Amazon and help us identify the Amazon wildlife that is on the photos taken by our 20 square kilometer grid of 78 cameras snapping away in the middle of the Amazon jungle

by Paul Bertner