Real-life bloodsuckers: think vampires don't exist? Meet some creatures with an appetite for blood.

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It's dinnertime, so Bill Schutt cracks open a bottle of cow's blood he has collected. He pours the red liquid into an ice cube tray. Don't worry, though, this blood meal isn't for Schutt. It's for his vampire bats. Schutt, a biologist at Long Island University in New York, spent three years as a graduate student raising two vampire bat colonies in order to study these mysterious blood drinkers. Each night, he would place the tray of blood within reach of his roosting bats so the hungry animals could lap up their gory supper.

Hanging out with these critters would give most people the creeps. But Schutt says some vampire bats are actually quite cute. "The white-winged vampire bat is like a little teddy bear and extremely gentle," he says. Others, like the common vampire bat, "can be nasty little creatures," he adds.

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Schutt's interest in vampiric animals led him to write Dark Banquet, a book about the unusual lives of sanguivores (animals that drink blood). He discovered that nature is filled with bloodthirsty animals. Find out how these parasites tap other organisms' most vital resource: blood.

MONSTROUS MEAL

Out of the 1,100 bat species, just three are out for blood. Vampire bats are found only in Central and South America. When the sun sets on these continents, the bats emerge from caves to search for their next meal.

Blood is a skimpy food source. It is about 80 percent water, with the rest being mostly protein. The red stuff contains almost no fat--a nutrient animals need to store energy. So vampire bats must consume half their weight in blood each night to stay alive.

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To get by on such a watered-down diet, it helps to be small. A vampire bat weighs about as much as a mouse, and it is one of the largest blood feeders. Other sanguivores, such as ticks and leeches, are even more pint-size. These creepy crawlies feed less often than bats do because they aren't as active.

STEALTHY HUNTERS

While surviving on blood is challenging, extracting this precious fluid is even more so. "Blood drinkers have to be stealthy to approach potential prey," says Schutt. Otherwise, they'd simply get swatted away.

Vampire bats creep up on sleeping birds and mammals, including humans, and use their razor-sharp teeth to make a small, painless incision. Like that of many sanguivores, vampire-bat saliva contains anticoagulants. These chemicals prevent blood from clotting. Unsuspecting victims usually snooze through the entire feeding session.

Most people don't realize when more common blood feeders, like ticks, have bitten them either. These relatives of spiders crawl across your body until they find a hidden spot. Then, the hitchhikers dig in with their skin-piercing mouthparts, which are lined with backward-facing barbs. Some ticks even secrete a cement-like substance to hold themselves in place. "Ticks had to invest in sneaky habits, because in order to steal blood, they have to be attached for days," says Thomas Mather, an entomologist (scientist who studies insects) at The University of Rhode Island. Unless discovered, ticks will feed for up to a week, filling with blood and swelling like balloons.

DANGEROUS BITE?

One of the biggest reasons to fear blood drinkers are the blood-borne diseases that many of them carry. In North America, ticks transmit several illnesses, including Lyme disease, which is caused by bacteria that attack a person's joints and nervous system. Vampire bats, blood-drinking flies, and especially mosquitoes can also carry an array of potentially deadly diseases.

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Not all sanguivores are bad for your health. Doctors have found that the leech Hirudo medicinalis can help people who have undergone surgery to reattach lost limbs. This aquatic worm normally uses its sucker-shaped mouth and saw-bladelike teeth to suck blood from a host. But if attached to a person's wounded limb, the leech can improve circulation to the body part with its blood sucking ability. Luckily, the treatment doesn't hurt: In addition to anticoagulants, leeches' saliva contains anesthetics, or painkilling substances, so patients feel only a tiny pinch.

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MORE BLOODTHIRSTY BEASTIES

Thousands of other sanguivores exist, from fleas, lice, and bedbugs, to even stranger bloodsuckers like the candiru fish. This one-to-two-inch-long catfish lurks in the Amazon River. It wriggles under the gill flaps of larger fish and chomps into their blood-rich gills.

Other animals may be Draculas-in-the-making. In the Galapagos Islands, a group of finches supplement their diet of nectar and seeds by attacking another resident bird, the booby. After one bird pecks to draw blood, other finches line up to take turns drinking from the wound.

Another part-time blood feeder--a new species of vampire moth that lives in Siberia--was recently discovered by Jennifer Zaspel, an entomologist at the University of Minnesota. The moths usually employ their sharp proboscis (feeding tube) to pierce the flesh of fruit. But when Zaspel and her team of researchers offered themselves as food, the moths used their proboscis to puncture the humans' skin and drink blood. "They treat you like a grapefruit or tomato and just start drilling in," says Zaspel.

Although sanguivores have gross eating habits, Schutt says we shouldn't wish for them to disappear. "As weird as these creatures are and as squeamish as people may be about them, vampires have an important place in nature. Some need conservation, and some can even be beneficial to us.

web extra

For more Information on vampiric animals, check out the link to Bill Schutt's Web site at: www.scholastic.com/scienceworld

nuts & bolts

Animals can be categorized by the type of food they eat. Sanguivores are organisms that live off blood. Herbivores consume only plants. Carnivores eat other animals. And omnivores eat both plants and animals.

PRE-READING PROMPTS:

* Can you think of any animals that drink blood?

* What is a parasite?

* What does a carnivore eat? An herbivore? What word do you think scientists use to categorize animals that get their nutrients from blood'?

DID YOU KNOW?

* Bloodletting, or draining a person's blood, was once wrongly believed to help cure diseases. The practice was used on George Washington when he was extremely ill with a throat infection and most likely hastened his death.

* The anticoagulant secreted by leeches is three to five times stronger than human-made anticlotting drugs.

* Many recipes from around the world use blood as their main ingredient, including blood soup, blood sausage, and blood bread.

CRITICAL THINKING:

* Vampires are all the rage in books and movies like the Twilight series. Based on what you've learned about the obstacles that bloodthirsty animals face in obtaining and surviving on blood, do you think it would be possible for fictional human vampires to live off this resource, assuming they had traditional human nutritional needs?

CROSS-CURRICULAR CONNECTIONS:

ART: Imagine you are a forest ranger and it is tick season. Because of the threat of Lyme disease, which ticks may carry, you need to teach hikers and campers how to avoid tick encounters and what to do if bitten. Create an illustrated poster to hang at the visitors' center using information found at: www.tickencounter.org/prevention.

RESOURCES

You can access these Web links at www.scholastic.com/scienceworld.

* Want to see more parasites in action? Meet the stars of the new Animal Planet show Monsters Inside Me, at: http://animal.discovery.com/tv/monsters-inside-me.

* Learn about the adventures National Geographic filmmakers had tracking down vampire bats in Nicaragua, here: www.nationalgeographic.com/fieldtales /bats/?fs=animals'nationalgeographic.com.

* Ghosts, monsters, and vampires got you scared? Then read Are You Afraid Yet? The Science Behind Scary Stuff, by Stephen James O'Meara, Kids Can Press, 2009.

DIRECTIONS: After reading the article about vampiric animals, fill in the blanks to complete the summary paragraph below.

Sanguivores are animals that -- --. A vampire -- is a sanguivore. But blood is a skimpy food source, and about 80 percent of it is -- with the rest being mainly --. Blood contains very little --, which is used to store energy, so a vampire bat needs to eat -- its weight in blood each night!

Answer

drink blood; bat; water, protein; fat, half