Blood Thirsty: Vampires, From Myth to Reality (part I).
The biology behind real vampires
∘ Vampires myth
∘ Feed to survive
∘ Vampires already exist
∘ How can vampires eat blood?
Vampires myth
Vampires have been the inspiration for a thousand captivating stories in every kind of media throughout history. They continue to be popular for the romantic mysticism represented in their mythology.
Probably the most classy and famous conception of a “vampire” comes from Dracula (1897), the renowned novel by Irish author Bram Stoker. This was possibly inspired by the Romanian Prince of Wallachia, Vlad Tepes Dracul, better known as “The Impaler’’, named for his brutal actions in the crusades against the Turks [1, 2].
However, beyond collective fantasy and copious stories in literature and contemporary films, there are organisms that indeed evolved their diet to feed on blood. This weird and creepy behaviour is called “hematophagy”, from the Greek etymologies háimatos (blood) and phagos (eat). Here, I will tell you how the fiction conception of vampires meets reality [3, 4].
Feed to survive
We all know that surviving is far from being an easy task and it is a continuous challenge for living things. One of the most basic ways to do that is to accomplish the energetic demands that the body needs for its optimal functioning. For many animals this requires ingesting from other beings.
Because of this need of eating, the way animals acquire its food is the target of something we call “natural selection”. Biologists understand it as the evolutionary mechanism that advantages certain characteristics suitable for its environment and what entails higher reproduction or survival compared to other individuals.
Feeding is an attribute that reaches an abundant variability of strategies, some of them are simple and others are tricky. We call these behaviours “foraging”, referring to methods for searching and obtaining food [5].
There is also a huge diversity of diets between animals, even for those closely related. As a feeding resource, one of the most curious and intriguing is blood. It is not just the spooky idea of sucking blood from an unsuspecting victim at night, but it also has many peculiarities; for instance, blood is composed of high doses of proteins (~20%) and water (~80%), and it lacks sugar and fats [6].
Vampires already exist
There are many animals that suck blood to feed on their victims, such as: leeches, lice, fleas, bed bugs, ticks, mosquitoes, lampreys, horseflies and bats [3]. It is to notice that between mammals, bats are unique having a diet like this [3, 9, 11].
Vampires or hematophagous bats are the most biologically specialized of the 925 species of living bats that we know (6, 8). Apparently, blood-base feeding appeared just once in the evolution of bats, and is currently preserved in only three species. Each of these species are medium to small in size from the Desmodontinae subfamily, and belong to the New World [6, 7].
Vampires have existed for a long time before they became the inspiration of legends. Fossil records of the first creatures like this are from different outcrops from the Pleistocene (around 10,000 years ago) in the Americas, many of which coincide with the current distribution of tropical zones [10].
Besides Dracula, the most famous hematophagous bat is the common vampire bat (Desmodus rotundus). Its distribution extends from central Mexico to northern Chile, Argentina and Uruguay [ 7, 9]. It’s by far the best known vampire species in terms of their biology. This was caused by an outbreak of rabies in the 30´s in Panama and Trinidad & Tobago. Populations of this species have grown up thanks to the increased availability of livestock that they feed on and their ability for nesting on sites beyond caves, different to many other bat species [7, 11, 12, 13, 14].
The other two species, hairy-legged (Diphylla ecaudata) and the white-winged vampire bat (Diaemus youngi) are less common and abundant. These species also share a similar distribution on the Neotropics, but prefer temperatures between 10 to 35 °C. Hairy-legged and white-winged bats also choose another kind of prey, being birds their favourites. Indeed, Diaemus also has specific metabolic adaptations for consuming bird´s blood (composed with more fats and less proteins compared to mammals) [15, 17].
How can vampires eat blood?
Just like fictional vampires that possess unnatural abilities, real vampires depend on a diverse list of morphological, physiological and behavioural adaptations [6, 9]. Hematophagous bats, like other bats, use echolocation for navigating through the environment and for locating potential prey.
They use their teeth without enamel and their sharp incisor fangs that help to cut skin like needles [6, 15, 18]. Its saliva contains a glycoprotein called “draculin” that promotes bleeding and prevents clotting, allowing bats to use its tongue lacking of taste buds for drinking blood like using a straw on a milkshake [6, 15, 18, 19]. In the particular case of the Desmodus r. (for short) , it has a leaf-nosed thermal sensor with the capacity to detect the warmth of superficial veins under the skin, which facilitates making an accurate bite [6, 7].
Their internal organs are different too, having a stomach and kidneys highly specialized for consuming blood; the rest of their digestive system has an accelerated rate for processing and eliminating the excess of water and urea from their prey [16, 20]. Even for movement, they have elongated thumbs that permit a proper hanging to their prey and also for easily moving in four legs to climb on its victims [16, 21].
All these special characteristics allow blood-sucking bats to eat blood as its fantasy counterparts. But there are intriguing questions left: how did bats adquire blood as food? Why do real vampires only exist in the American continent? These questions will be answered on another occasion. Nevertheless, either for classic stories or for mere scientific curiosity, vampires live “undead” in our culture, between us, as a story more ancient and mysterious than they ever could tell.
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