Beware the bat, comics and horror movies would have us believe. But out of the roughly 1,000 bat species that inhabit Earth, only three drink blood, and it’s usually just a sip from an unsuspecting cow. Bats picked up the bad rap when European explorers encountered the species in Central and South America in the 1500s and quickly associated them with vampire folklore.
Today, biologists have unearthed a variety of organisms that practice hematophagy, or drinking blood for food. Many are parasites. Some drink only blood to survive, while others include the nutrient-packed fluid as part of a balanced diet. Other animal vampires were bestowed with the ghoulish name because they are predators with fearsome reputations, or they simply looked scary and reminded early naturalists of the legendary bloodsuckers.
Whatever the origins of their names, these real-world vampires will have you under their spell:
Vampire Flying Frogs
A relatively recent discovery, the vampire flying frog inhabits the foggy cloud forests of southern Vietnam. With a red body and sharp, black fangs, Rhacophorus vampyrus certainly looks the part. But this frog is more cannibal than vampire. Using their big webbed feet and hands, the frogs glide and dive from tree to tree, spending their lives in the forest canopy. Females even lay their eggs inside tree holes with water pools. The tadpoles hatch and plop into the water, but with nothing there to eat, they wouldn’t last long. So the mamma frog returns and lays a batch of unfertilized eggs in the pool. With their trademark fangs, the tadpoles scoop up and scarf down the nutrient-rich eggs. Despite these finely tuned adaptations to the resource-poor environment, the vampire flying frog faces some considerable threats: climate change, a destructive fungus and habitat loss. The International Union for Conservation of Nature (IUCN) lists the species as endangered.
Among the finches of the Galapagos made famous by Charles Darwin, the vampire finch stands out as a species bizarrely adapted to its home on Wolf Island. A subspecies of sharp-beaked ground finch (Geospiza difficilis), these birds stealthily pluck and peck at the features of adult boobies until they draw blood to drink. The birds also scavenge for deceased booby chicks and unattended eggs. In somewhat creepy fashion, young vampire finches will gather to watch adult birds peck for blood or steal eggs to learn the tricks of the trade. Their sharp beaks are just as adept at puncturing fruit, and the vampire finch diet includes nectar, seeds and even bird vomit. It’s unclear why the larger boobies remain unperturbed by vampires drinking their blood, but the behavior may have evolved from a mutualistic relationship where the vampires cleaned booby feathers for food. And the finches aren’t the only vampiric birds in the Galapagos: Hood mockingbirds (Mimus macdonaldi) drink blood from the wounds of local seabirds.
Deep in the forests of Borneo lives a vicious, if tiny, predator. This nimble killer can take down a muntjak deer (Muntiacus muntjak) with a bite to the jugular, causing the deer to bleed to death so it may consume its heart and liver. So go local legends surrounding a species of tufted ground squirrel (Rheithrosciurus macrotis). However, given its remote home, the vampire squirrel remains largely unstudied, and no one is sure about the true extent of its predatory nature. One thing we do know is that the vampire squirrel has the fluffiest tail in the world. A study published earlier this year in the journal Taprobanica found that the squirrel’s tail is 30 percent larger than its body volume. Why is its tail is so bushy? It could be used to attract mates or warn fellow vampires of trouble. And before you worry about a walk in the woods, remember that the squirrel probably has more to fear from humans: The IUCN lists it as a vulnerable species due to habitat loss.
In the low-oxygen environment 300 to 3,000 meters below the sea’s surface lurks Vampyroteuthis infernalis, or “the vampire squid from hell”. Despite its fearsome name, it’s neither a vampire nor a squid. In 2012, researchers at the Monterey Bay Aquarium Research Institute discovered that the small cephalopod lives off marine snow, or particles of detritus (dead bodies, poop and snot) that float to the bottom of the ocean. The name comes from its dark red body and glowing eye spots, which give it a fearsome appearance. The animal is also well adapted for life in the shadows. In addition to its eight webbed arms, two long filaments extend out behind it sensing and capturing food. The filaments may also serve to detect larger predators, but since there’s not a lot to eat down there, the vampire squid is mostly free to mosey along as it pleases.
Two fish have garnered the nickname “vampire,” and both live up to the hype. In the Amazon and Orinoco rivers, a parasitic catfish called a candiru (Vandellia cirrhosa) subsists on the blood and tissue of other fish—and very occasionally humans. Its attack strategy for fish is to go for the gills. Swimming into the openings, the candiru latches onto arteries. Supposedly on extremely rare occasions, candiru will swim up the urethra of a human to feast on blood inside the body, but it’s hard to determine the accuracy of anecdotal cases.
The second vampire fish is the lamprey, seen above. Inhabitants of both fresh and a briny waters, these elongated fish lack jaws and scales. What they do have is teeth, and lots of them. Once a lamprey reaches adulthood, it can attach to an unsuspecting fish with the hook-like teeth inside its suction cup-like mouth, slurping up blood while swimming along. Though lampreys rarely attack humans (only when they’re really, really hungry), they have caused problems as an invasive species. In the 1800s, the Great Lakes were overrun with sea lampreys that arrived via artificial canals, and they significantly depleted the local fishing industry.
Though not a blood-consumer, Micavibrio aeruginosavorus is a vampire in the sense that it sucks the life out of other bacteria. When on the move, the bacterium grows a flagellum and paddles around in search of prey. Upon tracking down an unsuspecting victim, the microbe latches onto the bacterial cell and swallows the host’s nutrients, carbs, proteins and DNA. The host dies, and the vampire reproduces through binary fission. The vampire can even probe bacterial biofilms, the thin gooey films formed by some bacterial cells sticking together on a surface. Biofilms are extremely difficult for antibiotics to destroy, so the vampire’s abilities could make it useful as a sort of “living antibiotic” against drug-resistant microbes. Some studies suggest that M. aeruginosavorus can attack a wide variety of tiny targets, but they may prefer pneumonia species. Scientists have isolated M. aeruginosavorus specimens in wastewater, but they may inhabit other ecosystems as well.
In 2008, scientists discovered that a population of fruit-eating calpe moths (Calyptra thalictri) living in Siberia were on a weird diet kick. A team studying the moths set up a lab experiment where they presented moths with human hands, and surprisingly, the insects bit. Using their tongues, which are lined with spike structures, the moths pierced the skin and sucked blood. It turns out 10 out of the 17 species in the Calyptra genus are confirmed blood drinkers (usually from cattle or large mammals, but also humans). In all cases, fruit remains an important part of their diet, so how did these moths acquire their taste for blood? Moths have been observed feeding off tears, and it’s possible that the blood sucking evolved from a similar behavior. Only males drink blood, and they might be doing it to provide a salty, nutritious gift to the females during sex—a behavior that’s not uncommon in insects.
And So Many Other Bugs…
Roughly 14,000 insect species feed on blood. For bed bugs (Cimex lectularius), the secret weapon is their numbers: A female can lay up to 12 eggs in a day and up to 200 in her lifetime. All that feeding can be irritating but usually isn’t deadly. Other thirsty insects, though, have bites that come with a side of pathogen. Female mosquitos, like the Aedes aegypti seen above, are behind more human deaths than any other species due to the diseases they can pass to their victims, including malaria, dengue fever and West Nile virus. Perhaps the most widespread bloodsucking bug, ticks can drink up to 600 times their body weight in blood, and they are known for transmitting Lyme disease. Another bloodsucker of note, the kissing bug (Triatoma dimidiate) lives in caves in South and Central America and carries the parasite responsible for Chagas disease.