Some emerge at night, creeping up on their unsuspecting prey under cover of darkness. Others are so stealthy or well camouflaged that their victims never see them coming. Many of them have razor-sharp teeth, and some can jump up to 150 times their own height or defy assassination attempts. All, however, are after the same prize: warm, oozing blood.
While they might sound like characters in an Anne Rice vampire novel, animals ranging from leeches to bats and even birds consume blood. (Scroll down for a list of 10 real-life vampires.) "There's blood everywhere," points out Bill Schutt, vampire bat researcher and author of Dark Banquet: Blood and the Curious Lives of Blood-Feeding Creatures. "I'm surprised there aren't more animals that evolved to have it as part of their diet."
While so-called sanguivores are a diverse group, they face similar challenges in finding and feeding on blood, and have evolved a variety of adaptations to suit this specialized diet.
Most vampires are small, which helps them to evade detection. They have finely tuned sensory systems that home in on their next meal. Incredibly sharp teeth, or comparable tools, slice into flesh easily, decreasing the pain inflicted on the host. Finally, bloodsuckers have developed anti-coagulants that keep the red liquid flowing while they feed.
While sanguivores can be deadly—not because they drain you dry but because they carry diseases—many are merely nuisances to humans. In some cases we even benefit from them. Hirudin, for example, an anti-coagulant found in leech saliva, is used to prevent blood clots after surgery.
Here are 10 real, wild bloodsuckers.
The vampire finch of the Galapagos Islands is not, as Schutt says, a "card-carrying vampire." It sups on the red stuff in addition to its regular diet of seeds, nectar, and eggs.
The vampire finch, the only bird known to consume blood, acquires the liquid-iron supplement by pecking the wing and tail of the blue-footed booby until it bleeds. Only one bird will drink from the booby at a time, but others line up behind. "It's pretty comical to see three or four birds just waiting for the next bird to move away," says Schutt. "I guess this behavior evolved because if they swarmed the booby, it would get upset and move away." The booby doesn't appear to suffer any long-term damage from serving as a donor.
Lampreys are jawless fish that live mostly in coastal and fresh waters. Sometimes called eels because they have long eel-like bodies, they spend the first several years of their lives as harmless larvae. As adults, however, certain species are parasitic. These incredibly successful hunters attach themselves to other fish species and even marine mammals. They strike their quarry with their circular mouth, holding on with their hook-like teeth for hours or even days as they eat. While such attacks might kill smaller fish, victims that escape carry a visual reminder of the encounter: a circle-shaped scar.
Two parasitic lampreys, silver and chestnut, are native to the Great Lakes. Since the 1930s they've been competing with an invasive species, the sea lamprey, which Great Lakes officials have spent decades trying to combat and prevent from spreading further.
Of the world's more than 1,000 bat species, only three drink blood. These flying mammals, native to South America, Central America, and two Caribbean islands, are about the size of a mouse. They slip their slim, sharp incisors and canines into the flesh of mammals or birds, and then lick up the blood seeping from the wound (it keeps flowing because of anti-coagulants in their saliva), swallowing up to five teaspoons' worth—about half their body weight—in a feeding. "They have to feed on blood constantly," says Schutt. "Not only do they have to get it every night, but they have to get enough of it not to starve. These animals can starve to death in 48 hours."
The common vampire bat (which, as its name suggests, is the most widespread) feeds on the blood of cattle and other livestock. It creeps along the ground at night, and then springs up to three feet high onto its quarry.
The other two sanguivorous bats, the hairy-legged vampire and the white-winged vampire, prey on sleeping birds perched in trees. "They crawl underneath the branch, they crawl underneath the birds' foot, and they just use their teeth to flick one of those scales away," says Schutt. "The bird doesn't usually know anything as the bite is so sharp." White-winged vampire bats sometimes feed on chickens. One cozies up to the hen, nuzzling her like a chick, while another sneaks up behind to feed.
Vampire bats can carry rabies, and in warm, humid climates, the open wounds they cause are susceptible to infection.
All of the world's 2,000-plus flea species subsist on mammal blood. The insects can lie dormant in a cocoon for more than a year before they sense the body heat and vibrations that signal the presence of nearby hosts. Fleas have no wings, but they get by just fine without them: Their legs launch them into the air, to heights more than 200 times their own body length. Fleas have four rows of "teeth" that stab the skin to release a flow of blood. This tiny, paper-thin vampire will keep biting long after it's had its fill—up to 15 times its weight—passing the excess on to its larvae.
These eight-legged arachnids detect animals by their breath, odors, heat, moisture, or vibrations. They wait on the tips of grasses and shrubs, holding on with their third and fourth pair of legs; when a meal brushes by they climb on and crawl to a suitable place to dig in. They attach firmly—some secrete a cement-like substance to keep them locked in place—and feed for days, becoming grossly engorged, with some consuming up to 600 times their weight in blood.
There are two major categories of ticks: soft and hard. Hard ticks have a hard shield behind their mouthparts (often incorrectly called the "head") and feed primarily on humans and other large mammals. Soft ticks, which lack the shield, typically prey on birds or bats.
Despite their small size, ticks are among the most-feared vampires, because they transmit illness such as Lyme disease, Colorado tick fever, Rocky Mountain spotted fever, African tick bite fever, and numerous other maladies.
The bedbug may be the bloodsucker that most people are likeliest to encounter. "All the things that humans love, like clutter and travel, are the kinds of things that these creatures have become adapted to," says Schutt. These bloodsuckers are remarkably resilient. They disappear during the day—into cracks and crevices, in bedding and furniture—and emerge at night to feed. They can survive for 18 months without a meal, and they've developed resistance to pesticides. Perhaps it's not surprising that such a tough creature would display a violent mating behavior, known as traumatic insemination: The male stabs the female's abdominal wall and injects his sperm directly into the wound.
While bedbugs are undeniably bothersome, so far they haven't been shown to transmit diseases to humans.
This candiru is an inch-long fish, related to the catfish, that inhabits the Amazon and Orinoco rivers. It locates its victim by following a trail of nitrogen compounds that wash out of the gills of larger fish. The candiru then slips in beside the rich blood vessels beneath the fish's gill and, using its spine-covered head, scrapes away until it draws blood.
In 1997 a Brazilian man claimed that while he was urinating in a river, a candiru swam up and into his urethra. Doctors removed a 13-centimeter-long specimen, but the account has been met with extensive skepticism.
"Assassin" isn't an exaggeration with these bugs, which are known to mimic prey caught in a spider's web by plucking and stretching the silk of the webs with their front legs. When the spider comes to collect its meal—bam! The assassin bug seizes it in its forelegs and simultaneously stabs it with its mouthpart, a needle-like, double-barreled proboscis. The bug injects saliva, containing anti-coagulants, while it sucks up blood.
The bugs also feed on people, and transmit a pathogenic bacterium that can cause Chagas disease, a serious disorder that affects the heart, digestive system, and nervous system.
All of the more than 2,700 species consume water and nectar, but only the females drink blood, using the protein and iron from the liquid to make their eggs. Females detect their prey by movement, odor, carbon dioxide, and body heat. They siphon the blood through their proboscis.
In addition to being a great nuisance that leaves behind itchy welts (a reaction to the anti-coagulants in the saliva), the female mosquito is certainly the deadliest vampire to humans, because she transmits malaria, West Nile, yellow fever, and many other diseases. In 2010 alone, the World Health Organization reports, there were approximately 219 million malaria cases worldwide and 660,000 deaths. In addition to preventive measures and existing drugs, health officials are testing vaccines against the malaria-causing parasite that mosquitoes carry.
Leeches are essentially big stomachs. All have adapted an enormous gastric tissue that takes up the majority of their bodies. "So most of them can feed on blood up to five to eight times their unfed body weight," says Mark Siddall, a leech expert from the American Museum of Natural History.
The suckers use one of two different kinds of feeding mechanisms. Leeches that dine on turtles, frogs, and birds have a muscular proboscis (a modified throat tissue tube) that they use to penetrate the host's capillaries. Medicinal or terrestrial leeches, meanwhile, have three circular ridges, or jaws, with a series of hard, spiky teeth that cut into tissue. Once cut, the leeches use their mouth to apply suction to the blood, pulling it into their guts.
Contrary to popular belief, there's no scientific evidence that leeches possess an anesthetic in their saliva to keep their prey from detecting them. "My suspicion is that most people don't feel a leech bite because when you are in water your skin is desensitized by the coldness of the water and because you are constantly feeling movement of water," explains Siddall. "It's also a very small incision."
Humans have long (and sometimes misguidedly) depended on leeches for medical purposes. Today these animals are used in certain types of microsurgery to promote healing and restore circulation.