While famous vampires, such as Count Dracula and Mr. Sparkles himself, Edward, from Stephenie Meyer’s Twilight saga, may be the stuff of fantasy, mammalian bloodsuckers aren’t an entirely fictional concept. Indeed, real-life vampires haunt the moonlit nights of Central and South America. While these creatures are not particularly humanoid, they are more closely related to us than you might think. Like all mammals, they are covered in body hair, produce milk to nurse their young, and give birth to live infants—just like us. But, they fly… I’m talking about vampire bats! Read on to learn about the fascinating and slightly unsavory habits of our bloodsucking relatives.
Vampire bats roosting together in caves. Left: common vampire bats (Desmodus rotundus) [Photo by: Tomás Carranza Perales]. Right: hairy-legged vampire bats (Diphylla ecuadata) [Photo by: Sebastian K. Herzog].
There are three genera of vampire bats that each contain a single extant species: the common vampire bat (Desmodus rotundus), the hairy-legged vampire bat (Diphylla ecuadata), and the white-winged vampire bat (Diaemus youngi). All three extant species currently exist in wide overlapping ranges of Central and South America. (Sorry to disappoint fans of Indiana Jones and The Temple of Doom, which includes a scene where Dr. Jones warns his companions of giant vampire bats flying above them, but these are actually flying foxes, also known as fruit bats. No species of vampire bat exists in India, where the film takes place.) Nevertheless, some extinct vampire bat species had wider homeranges. For example, the Stock’s vampire bat (Desmodus stocki) lived 2.5 million years ago years ago during the Pleistocene and ranged across broad swaths of the southern region of North America, including present day Arizona, West Virginia, and Florida [1,2]. Unlike in Indiana Jones, giant vampire bats are long gone. However, extinct species of giant vampire bats (Desmodus draculae) did patrol the night skies in Central and South America during the Pleistocene and early Holocene [3]. They likely vanished with their prey, megafauna such as the giant ground sloth (Megatherium americanus), which was hunted to extinction upon early human settlement of South America [4]. Luckily, for those who venture into the jungles of Central and South America today, you won’t encounter a vampire bat with a wingspan of more than 12 inches. If you were to travel to the same regions 2.5 million years ago, however, you could have encountered a vampire with a wingspan of up to 6 feet [5]!
Vampire bats are the only mammals known to be obligate hematophages, which means they subsist entirely on blood. The preferred prey type for the common vampire bat (D. rotundus) are European cattle species and other large domesticated mammals used in agriculture, while the other two species of vampire prefer to feed on large birds and small mammals [6]. They primarily hunt and feed at night, which facilitates the stealthy movements required to extract blood from unsuspecting animals. During the day, they tend to congregate in roosts to rest and socialize.
Vampire bats have evolved a suite of highly specialized behavioral and physical characteristics that help them get “blood meals” from other mammals. These adaptations include large canine teeth, lateral tongue grooves to slurp up blood, well-developed thumbs and hindlimbs for clinging to prey, acute senses of sight and smell, and salivary anticoagulants that maker prey bleed continuously during a vampire’s feeding session [7]. These adaptations are estimated to have evolved within the last 4 million years, making this possibly one of the quickest examples of directional selection (when traits evolve by natural selection unidirectionally towards a more extreme version) in mammals [8].
Vampires feed in a process called sanguination. Sanguination consists of four stages: selection of the feeding site, preparation of the feeding site, shaving of the intended area for wounding, and, finally, the bite [9]. After a single feeding bout, a vampire can hold up to 43% of their body weight in blood, however, vampires lack the ability to store fat, so they immediately begin urinating after feeding to excrete excess energy [10]. As a result, vampire bats have some of the most active kidneys of any mammal. Further, if a vampire goes more than two days without obtaining a blood meal, it will die [11]. This extremely harsh physiological constraint on vampires plays a major role in how their social systems are structured, particularly by facilitating a social mechanism for fat storage, known as blood meal sharing. This has led many researchers to become interested in studying these animals to better understand cooperation and social strategies.
Vampires are a social species in which populations assort themselves into roosts, which can be anything from caves to hollowed-out trees. Even man-made structures, such as bridges and wells, provide daytime roosting sites. Vampires bond with one another by grooming, a process which facilitates the formation of social networks. A social network is any number of individuals interconnected via social ties [12]. These social networks play a vital role in individual survival. Because finding a blood meal each day is so hit-or-miss, vampires often rely on their social conspecifics to donate blood to them when they are starving. This “donation” process occurs when starving bats find bats in their roost that were successful at feeding and beg them for a blood meal. If the successful bat agrees, she will regurgitate some of her blood into the mouth of the starving bat [11] (see video above). Gross, but as my mom always told me, “Don’t yuck someone else’s yum.” This clever cooperative system has allowed vampires to survive for over 4 million years, even when faced with harsh conditions that may lead to individual bats being unsuccessful in their nightly hunts. Blood meal sharing, and by extension the social networks which facilitate this cooperative behavior, are imperative for survival. In a way, these sharing networks can be conceptualized as a social mechanism for fat storage, as starving bats must rely on their social partners for energy when they fail to feed on a given night.
Whereas 25% of terrestrial mammalian species are threatened with extinction [13], the IUCN classifies vampire bats as of “least concern,” meaning they are not under threat of extinction. As a matter of fact, the range in which these animals are found has been rapidly increasing—and may one day include southern portions of the United States [14]. However, recently South American ranchers have started urging their governments to target vampire bats as a way of reducing the transmission of rabies, as well as other diseases they are known to carry. While disease risk is important to consider, these beautiful and fascinating animals have other qualities related to human health which help balance the scales of the argument for or against their extermination. For example, the anticoagulatory properties of their saliva are one of the most effective chemical compounds for treating blood clots associated with strokes [7]. And even beyond their utilitarian uses, vampire bats exhibit behaviors and personalities that mirror our own in many ways. They form strong bonds with conspecifics, akin to friendships, and cooperate in ways that ensure the survival of others, much like human societies do. Even while exhibiting behaviors and a lifestyle that can evoke images of terrifying bloodsucking creatures of fantasy, upon a closer inspection of how these animals behave and exist, one can’t help but see a bit of humanity in them as well.
[Cover image of hairy-legged vampire bat (Diphylla ecaudata) by Jose G. Martinez-Fonsecaz]
J.P. Calcitrai is a third year PhD student in the Animal Behavior program at UC Davis. His research focuses on the evolution of sociality in mammals. Outside of academia, JP enjoys hiking and backpacking, writing short stories, and tinkering with computers and other electronic devices.
References:
[1] Grady F., Arroyo-Cabrales, J., Garton, E.R. (2002). The northernmost occurrence of the Pleistocene vampire bat Desmodus stocki Jones (Chrioptera: Phyllostomatidae: Desmodontinae) in Eastern North America. Smithsonian Contribution to Paleobiology 93:73- 75.
[2] Czaplewski, N.J., and Peachey, W.D. (2003). Late Pleistocene bats from Arkenstone Cave, Arizona. The Southwestern Naturalist 48(4):597-609.
[3] Brizuela, S., & Tassara, D. A. (2021). New record of the vampire Desmodus draculae (Chiroptera) from the Late Pleistocene of Argentina. Ameghiniana, 58(2), 169-176.
[4] Politis, G. G., Messineo, P. G., Stafford Jr, T. W., & Lindsey, E. L. (2019). Campo Laborde: a Late Pleistocene giant ground sloth kill and butchering site in the Pampas. Science advances, 5(3), eaau4546.
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[8] Baker, R. J., Bininda-Emonds, O. R. P., Mantilla-Meluk, H., Porter, C. A., & Van Den Bussche, R. A. (2012). Molecular time scale of diversification of feeding strategy and morphology in New World Leaf-Nosed Bats (Phyllostomidae): a phylogenetic perspective. In Gunnell, G. F. & Simmons, N. B. ed. Evolutionary History of Bats: Fossils, Molecules and Morphology. Oxford University Press. 385-409.
[9] Greenhall, A. M. (1972). The biting and feeding habits of the vampire bat, Desmodus rotundus. Journal of Zoology, 168(4), 451-461.
[10] McFarland, W. N., & Wimsatt, W. A. (1969). Renal function and its relation to the ecology of the vampire bat, Desmodus rotundus. Comparative Biochemistry and Physiology, 28(3), 985-1006.
[11] Wilkinson, G. S. (1984). Reciprocal food sharing in the vampire bat. Nature, 308(5955), 181-184.
[12] Krause, J., James, R., Franks, D. W., & Croft, D. P. (Eds.). (2015). Animal social networks. Oxford University Press, USA.
[13] Hoffmann, M., Brooks, T. M., Da Fonseca, G. A. B., Gascon, C., Hawkins, A. F. A., James, R. E., … & Silva, J. M. C. (2008). Conservation planning and the IUCN Red List. Endangered Species Research, 6(2), 113-125.
[14] Bodenchuk, M. J., & Bergman, D. L. (2020). Vampire Bats: Preparing for Range Expansion into the US. In Proceedings of the Vertebrate Pest Conference (Vol. 29, No. 29).
[Edited by Alice Michel and Jacob Johnson]
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