Vampire Bats: Drinking Blood Is in Their Genes

vampire bat

Story at-a-glance -

  • There are three types of mammals that survive solely on the blood of their prey, and all three are vampire bats; drinking blood, scientists report, is literally part of their DNA
  • Although the blood-borne pathogens found in vampire bats’ guts include around 280 pathogenic bacterial species, it doesn’t seem to make them get sick and die as it would other animal species
  • Vampire bats weigh around 2 ounces, and when they need to feed, they creep along the ground among sleeping livestock looking for a “target” to climb onto, making use of heat sensors around their noses
  • An area of vampire bats’ brains processes in a way that helps them detect the deep and even breathing patterns of a potential victim that indicates their prey is sleeping before they climb on and look for a place to bite
  • The bite sites of vampire bats are so small the animals who’ve been bitten rarely wake up, not only because the bats’ saliva contains a painkiller, but also because it prevents clotting so that the blood flow is constant until the bats have eaten their fill

By Dr. Karen Shaw Becker

You may already be aware that bats are mammals, but did you know they make up fully a quarter of the mammals in the world? And perhaps you were aware that bats are voracious insect eaters, especially attracted to mosquitoes (which is ironic, since mosquitoes are blood-suckers, too). But maybe if you knew that vampire bats survive solely on the blood of their prey, it was a fact you quickly scrubbed from your brain.

Yes, bats do a lot of good, ridding the planet of mosquitoes to the incredible degree that they do, but one factoid scientists have discovered recently is that some bats are able to survive exclusively on blood because it’s literally in their genes.

In fact, the complete genome of the vampire bat has been “mapped,” revealing a number of fascinatingly unique facts regarding the detriments of what Reuters called the flying mammal’s “exotic food source,” most significantly because it exposes them to blood-borne pathogens.

The Desmodus rotundus, also known as the common vampire bat, as well as white-winged vampire bats (Diaemus youngi) and the hairy-legged vampire bat (Diphylla ecaudata), are the only mammals in the world that survive on nothing but blood; however, the latter two mainly feed on the blood of birds.

Vampire bats’ genome compared to that of their cousins whose diets include fruit, nectar, insects and meat (which makes them omnivores), and microbial DNA from their droppings, were scrutinized. According to NASA Space Radiation Lab (NSRL), there are a minimum of 160 known bat species in this group, known as the phyllostomid family.

Hailing from areas hugging the western coast of South America, Central America, Mexico and Costa Rica, as well as Trinidad in the West Indies, the common vampire bat is a nocturnal cave-dweller that feeds on the blood of livestock such as cattle and horses. Keep in mind that these bats only weigh around 2 ounces and have a wingspan that generally measures 7 to 15 inches.

Bat Science

University of Copenhagen doctoral student and lead study author Lisandra Zepeda Mendoza, whose research was published in the journal Nature Ecology & Evolution,1 explained that genome elements from bats’ immune response and viral defenses are designed to help them stave off harmful microorganisms that might be stored in the blood.

In addition, the researchers looked for genes involved in helping the bats metabolize fats and vitamins needed to assimilate the proteins and other nutritional attributes of their plasma diet. As Zepeda Mendoza noted:

“We decided to study this species because it has an ‘extreme’ diet, in the sense that it requires many adaptations in the organism to live on that. Blood is a challenging dietary source since it provides very low levels of vitamins and carbs, and a lot of proteins, salts and waste products.”2

Oddly, the researchers found that the gut microbiomes of vampire bats contained more than 280 pathogenic bacterial species. Many of them had been transmitted by ticks and fleas, which are also blood suckers that often cause diseases in other mammals. Why weren’t vampire bats susceptible, as well?

Michelle Baker, a bat immunologist at the Commonwealth Science and Industrial Research Organisation (CSIRO) Australian Animal Health Laboratory, says that when humans are exposed to pathogens, proteins called interferons are automatically “switched on,” which in turn results in the switching on of hundreds of other genes to activate “anti-viral players” to deal with the infection.

When no longer infected, your interferons switch off. But too much interferon activity can trigger autoimmunity in humans. These bats, however, don’t have interferons that switch off, which is what keeps them from succumbing to disease. For humans, she explains:

“The reason we don't want it switched on all the time is it can be quite toxic. It’s an inflammatory response so you only want to switch it on when you need to deal with something.”3

It’s a fact that vampire bats deserve their designation as sanguivores, or organisms that make their living, so to speak, on the blood of other animals. But ABC News maintains that one reason vampire bats survive to thrive is likely due to transposons — aka stretches of DNA — that can multiply and shift around the genome.

“It’s why they’re dubbed jumping genes. Human DNA is rife with transposons. For instance, the ‘Alu element’ is a DNA sequence about 300 letters long, but is repeated so often, it comprises around 10 per cent of our total genome. The phenomenon was first spotted in the 1940s by American geneticist Barbara McClintock, when she noticed some maize genes seemed to be mobile.”4

The Bloody Truth About Vampire Bats

Incredibly, bats land near prey in the dark (being nocturnal) and walk on the ground to reach sleeping animals. Then they use their razor-sharp teeth to puncture the animals’ skin, and then use their long tongues to lap up the blood. But where and when did such bat blood-letting begin? NSRL tackles that question, hypothesizing that it all took place around 4 million years ago:

“Recent genetic studies have determined that the vampires diverged from the remainder of the Phyllostomid family about 26 million years ago. Blood-feeding is thought to have evolved only once, in a common ancestor that is shared by the three vampire bat species of today.

Some researchers suspect that the first vampire bats may have evolved from insect-eating bats that were feeding on the parasites of birds and mammals. Thus, the bats were consuming a partial diet of blood (the blood that the parasites had eaten), and when they pulled the parasites off the bird or mammal, they were further exposed to blood at the attachment site.”5

Research indicates there’s an area of the bats’ brains that can process the deep, even breathing patterns that indicate their prey is sleeping before they climb on and look for a place to bite, making use of heat sensors around their noses.

The bite site is only 3 to 5 millimeters deep and the same width, and the victim rarely even feels it. In fact, some of the proteins that researchers discovered in bat saliva also function as painkillers. Rather than sucking blood, they lap it up with the help of lateral grooves on their tongues’ undersides.

Blood-Eating Bat Processes and Genetic Changes

It’s interesting to note that leeches and vampire bats, which are said to be “evolutionarily separate,” share a common but modified gene. This, scientists say, took place through a process called “gene recruitment,” which resulted in properties allowing for anticoagulant leech saliva and vampire bat saliva, which prevents blood from clotting at a victim’s wound site.

Gene recruitment is descried as a phenomenon that involves genes “originally evolved for one function for a purpose in a new biological function.”6 In 2015, Robert J. Baker, Ph.D., and Caleb D. Phillips, Ph.D., used cutting-edge technology at Texas Tech University to study the evolution of blood eating in bats.

Anticoagulant (anti-clotting) elements keep the blood flowing. In this way they can consume about 2 tablespoons in about 20 minutes, which is all they need in a day to survive. Further, they don’t require another feeding for two or three days. In case you’re curious about the following aspects of the digestion process, NSRL explains:

“The digestive tract, circulatory system, and kidneys of the vampire bat are especially developed for rapid processing and digestion of blood. The stomach lining rapidly absorbs the blood plasma, and the plasma is transported quickly to the kidneys and then the bladder for excretion.

A common vampire bat begins to excrete very dilute urine within two minutes of feeding. This shedding of much of the water-weight from a meal is necessary to allow the bat to fly and return to its roost.”7

Vampire Bats: A Blood-Sucking Reputation

People who are slightly squeamish may not be able to keep themselves from associating bats with Bram Stoker’s 1897 horror classic, Dracula. Zepeda Mendoza doesn’t judge. While she does characterize them as either “messed up or amazing creatures, whichever you want to call them,” she continues:

“My personal feelings about them is that it’s too bad people demonize them like that. We should be amazed by them, not scared. They’re actually quite cute: abstract beauty. Sure, you don’t want them to bite your cows if you’re a farmer, but they were there way before you.”8

That may be true, but while there’s quite a leap between all the hype about the fictional “undead” vampire and vampire bats, sadly there are other negative connotations with the concept. NSRL notes that stories of blood-feasting human-like beasts targeting humans may have been spawned as early as the mid-1300s. Such a creature was the only way the head-scratching enigma that such horrific diseases as the Black Plague could be explained, not to mention anemia. The NSRL site observes:

“After early reports by New World explorers of blood-feeding bats, folklore surrounding vampires rapidly incorporated ‘winged creatures of the night’ into these myths. The elusiveness, mystery, and nocturnal habits of both bats and these mythological creatures contribute to this folklore connection.”9

Blood is, at the very least, an “extreme” type of diet, and it’s very, very rare that a species should live on it, Zepeda Mendoza asserts. According to ABC News, what scientists have learned from their latest research on bats might be helpful in treating viral infections in humans.

Bat saliva, it turns out, has such unique properties that scientists have even tapped it for use in medical applications. A genetically engineered medication known as desmoteplase takes advantage of the anticoagulant properties that’s been looked at in clinical trials for use in ischemic stroke patients, or people with blood clots in their brains.

Scientists also believe it may help break up blood clots better than traditional drugs and possibly increase the treatment time frame for stroke victims. Such a unique structure has proved useful, which seems to suggest that there are more than a few positives connected to the “dreaded” vampire bat.