Nature's Real Vampires
10 Animals That Want to Suck Your Blood.
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.