11 Bloody Facts About Vampire Bats

iStock / through-my-lens
iStock / through-my-lens

Bats are firmly rooted in Western vampire lore, but only three species, out of some 1100 in the order Chiroptera, actually have a taste for blood. The vampire bats are the only mammals in the world that live on blood alone, and the unique challenges of that diet make them some of the most specialized, fascinating and downright weird animals that nature has to offer.

1. The three vampire bat species—the common vampire bat (Desmodus rotundus), the hairy-legged vampire bat (Diphylla ecaudata), and the white-winged vampire bat (Diaemus youngi)—are closely related and grouped together in the subfamily Desmodontinae. Their ranges overlap in parts of Central and South America, so, in what might be an effort to avoid competition with each other, the species specialize in different prey. The common vampire feeds primarily on the blood of mammals —ranging from tapirs to horses to the occasional human—and seems to have a preference for livestock animals. The hairy-legged vampire, meanwhile, lives almost exclusively on bird blood, while the white-winged vampire is more versatile and drinks from both birds and mammals.

2. Other bats with less grisly diets got a bad rap from European explorers in the Americas. The Europeans had heard stories about blood-drinking bats and encountered native people and livestock that had been bitten in the night and, without any real knowledge of the animals’ diets, began labeling different bats as vampires willy nilly, usually applying the term to bigger and/or uglier ones. Bats that lived on insects or even fruit were assumed to be vampires thanks to their appearance, and the association stuck when they were scientifically described and saddled with names like Vampyrum spectrum and Pteropus vampyrus. Meanwhile, when a naturalist finally got his hands on an actual vampire, D. rotundus, no one one believed his assertions that it drank blood, and he made no mention of it in his description.

3. When the bats feed, they use their teeth to shear away hair or feathers from a small spot and then cut into their victim’s flesh with their sharp incisors. (According to zoologists at Chicago’s Field Museum, even the teeth on old, preserved bat skulls in museum collections are sharp enough to cut someone handling them carelessly.) Rather than actively suck the blood from the wound like their namesakes, the bats let the physics of capillary action do the work. They lap at the blood and specialized grooves on their lips, tongues, and/or roof or their mouths suction it up. A protein in the bats’ saliva called a plasminogen activator prevents the blood from clotting and keeps it flowing freely while they drink.

4. White-winged vampires have a few tricks for feeding on domestic chickens without startling the birds. Sometimes, they’ll approach a hen and mimic a chick by nuzzling up to her brood patch. This featherless section of skin on the hen’s underside is densely packed with blood vessels and is used to transfer heat to her eggs or chicks during nesting. The vessels make an easy target for the bat, and if the hen thinks it's her baby cuddling up to her, she’ll sit on the bat to give it access to drink. Other times, the bats will climb up on a hen’s back, mimicking the touch and weight of a mounting rooster and sending the hen into the crouching stance they take before mating. The bat can then shimmy up to the hen’s neck for a bite and she’ll stay in that position until the bat hops off.

5. White-winged vampires will also take their meals in the trees instead of the barnyard. While a bird roosts on a branch, the bat sneaks up on it from below, crawling along the underside of the branch and staying out of sight. Once it’s directly underneath its prey, the bat bites the bird’s big rear-pointing toe and drinks its fill.

6. The hairy-legged vampire also feeds in the trees, but doesn’t bother with subtlety like its cousin. They’ll often land directly on a bird and hang from its body upside-down with their feet while biting around the bird’s cloaca, the all-purpose entrance and exit for the intestinal, reproductive, and urinary tracts. The maneuver is helped by the bat’s calcar, a bony spur that comes off the ankle bone. It’s absent in some bats and underdeveloped in others, but the hairy-legged vampire’s protrudes noticeably and is used by the bat like an extra digit to help it hang on.

7. Unlike its cousins, the common vampire bat eats solely on the ground, and it has evolved to be as nimble there as it is in flight. While most other bats are awkward crawlers, the common vampire can move with a quick run-like gait or hop along the ground, supporting its weight on its hind legs and using its wings and elongated thumbs to steer and push off of the ground. This comes in handy for chasing after prey on the move and for jumping out of the way if it needs to.

Feeding for common vampires is often risky, given that their preferred victim, the domestic cow, is several thousand times larger than they are. They usually bite cows on the area of the leg just above and behind the hoof, since the skin is relatively thin and the blood vessels run close to the surface. One step backwards, and a bat could be squashed if it hadn’t figured out how to run or make impressive three-foot leaps into the air.

8. To meet their energy needs, vampire bats need to drink about an ounce of blood at every meal, meaning they consume half their body weight during each 20 to 30 minute feeding session. Their bodies have adapted to lighten that load, and their stomach lining rapidly absorbs much of the blood’s water content and sends it to the kidneys so it can be excreted. The bats can process their meal so quickly that they may begin disposing of it before they’re even finished with it, and start urinating just a few minutes into the feeding.

9. Vampires are known to share meals with each other. Mother bats regurgitate previously-drunk blood for their offspring until the babies are old enough to hunt on their own. Other related bats and even unrelated ones have also been observed puking blood up for one another in a reciprocal arrangement. If a bat can’t find a meal one night, one of its roost-mates may share some of its meal. In the future, the bat who was fed is highly likely to return the favor. If it cheats, or takes a blood donation without ever giving back, it may find that it gets the cold shoulder the next time it needs help.

10. Vampire bats have a few different tools for finding their food. They have well-developed senses of smell and, despite bats’ reputation, keen eyesight. They’ve also got heat-seeking faces—their wrinkly, leaf shaped noses are loaded with nerves that are, in turn, loaded with proteins that are sensitive to the infrared radiation given off by warm-blooded animals. They also have finely-tuned hearing and specialized neurons that react only to the sound of breathing. They can even distinguish the breathing sounds made by different individuals, and may be able to remember the unique sonic components of an individual animal’s breathing, allowing them to return to the same reliable source of blood night after night.

11. Animals that are adventurous eaters learn to avoid potentially toxic foods through trial and error. They try something new, get sick, and then avoid those flavors in the future. Vampire bats appear to have lost their sense of taste aversion, though. In experiments, biologists have given vampire bats and their fruit- and insect-eating cousins treats seasoned with different, unfamiliar flavors, and then induced vomiting. At their next few meals, the bats were given the choice between normal food and food flavored with the same seasonings from before. While the other bats avoided the flavors they associated with getting sick after the first meal, the vampires dug in to both flavored and unflavored blood. The researchers think that the vampires either lost the ability to make these associations because their diet doesn’t present a variety of flavors and it wasn’t needed, or maybe that they had to lose it early on in their blood-drinking history to make the diet viable.

11 Amazing Facts About Alligators

Cindy Larson/iStock via Getty Images
Cindy Larson/iStock via Getty Images

Alligators are pretty terrifying as they are, but scientists are making discoveries about the reptilian ambush predators that only add to that reputation.

1. Alligators have an extremely powerful bite.

You really, really don’t want to be bitten by an alligator. A 2004 study of wild and captive alligators found that large individuals bite down with 13,172 Newtons—or 2960 pounds—of force, one of the most powerful bites ever recorded for a living animal [PDF].

2. Alligators can consume almost a quarter of their body weight in one meal.

Alligators don’t have a problem with their eyes being bigger than their stomachs. Thanks to a special blood vessel—the second aorta—they’re able to shunt blood away from their lungs and towards their stomachs, stimulating the production of strong stomach acids to break down their meals faster. Juvenile alligators are capable of eating about 23 percent of their body weight in a sitting, which is equivalent to a 180-pound person eating more than 41 pounds of steak au poivre at a meal.

3. Alligators eat their young.

One of the biggest threats to an American alligator? Other alligators. When alligators are born they’re small enough to be light snacks for their older neighbors, and a 2011 study estimated that, in one Florida lake, bigger alligators ate 6 to 7 percent of the juvenile population every year.

4. An alligator's stomach can dissolve bones.

Alligator resting on a log in a swamp
cbeverly/iStock via Getty Images

An alligator stomach is a hostile environment. Their stomach acids have a pH of less than 2—in the range of lemon juice and vinegar—and most soft-bodied prey is totally digested in two to three days. If you wound up in a gator stomach, however, you'd stick around a bit longer. Bone and other hard parts can take 13 to 100 days to disappear completely.

5. Alligators have antibiotic blood.

Alligators are tough—and not just because of the bony armor in their skins. Serum in American alligator blood is incredibly effective at combating bacteria and viruses, meaning that even alligators that lose limbs in mucky swamps often avoid infection.

6. Prehistoric ancestors of today's alligators lived 70 million years ago.

Alligator forerunners and relatives have been around for a very long time. The largest was Deinosuchus, a 40-foot alligatoroid that lurked in coastal habitats all over North America around 70 million years ago. Damaged bones suggest that unwary dinosaurs were a regular part of the “terrible crocodile's” diet. Fortunately, modern American alligators don’t come anywhere close to measuring up.

7. Alligator pairs often stick together.

A decade-long genetic study of Louisiana alligators found that some females paired with the same males multiple times, with one in particular choosing the same mate in 1997, 2002, and 2005. Even some females that mated with multiple partners still showed long-term fidelity to particular males.

8. Alligators love fruit.

Baby alligator riding on an adult's back
BlueBarronPhoto/iStock via Getty Images

Alligators aren’t strict carnivores. They also eat fruit when they get the chance, and might be important seed-dispersers. That might not sound so scary at first, but just watch this video of an alligator mashing a watermelon.

9. Despite their short legs, alligators can climb trees.

While on the lookout for alligators, you should remember to occasionally look up. American alligators, as well as several other species of crocodilian, are surprisingly accomplished climbers [PDF]. As long as there’s enough of an incline for them to haul themselves up, gators can climb trees to get to a better basking spot, or get the drop on you, as the case may be.

10. Alligators use tools to lure their prey.

Alligators might be reptilian innovators. Scientists have observed Indian and American species of alligator luring waterbirds by placing sticks and twigs across their snouts while they remain submerged. When the birds go to pick up the twigs for nesting material, the gators chomp. 

11. Alligators have no vocal cords, but they still make sounds.

Alligators are among the most vocal reptiles, despite not having vocal cords. By sucking in and then expelling air from their lungs, they can make different sounds to defend their territory, call to mates or their young, or fight off competitors—such as a guttural hiss or a frankly terrifying bellow.

It’s Raining Iguanas In South Florida

passion4nature, iStock via Getty Images
passion4nature, iStock via Getty Images

Florida is known for its extreme weather, but a recent alert issued in Miami on Tuesday, January 21 was strange even for locals. As CNN reports, the National Weather Service's South Florida bureau warned of iguanas falling from the trees as temperatures approached freezing.

Thermometers rarely read below 50°F in South Florida, but this week temperatures dropped into the 40s and 30s. At higher latitudes, a chilly forecast means you should probably wear a coat, but in tropical regions, you may need to grab an umbrella as well to protect yourself from iguana showers.

The invasive reptile species is cold-blooded, which means its body temperature is dependent on its environment rather than self-regulated. Many iguanas never have to deal with cold snaps, but when temperatures do plummet, they have an adaptation that helps them survive. If it's colder than 50°F, the lizards become lethargic, and if it drops below 45°F, they enter a catatonic state. Their lungs still work, their heart still beats, but nonessential body functions shut down in order to conserve energy. The video below shows iguanas in this state during a cold Florida winter two years ago.

Those dodging falling iguanas can take comfort in the fact that the creatures aren't necessarily dead, even if they appear to be. But the clever survival trick only works for so long. After enduring near-freezing temperatures for eight hours or longer, dormant iguanas start to die. Fortunately for Miami residents of all species, temperatures there are expected to reach a high of 65°F later today.

[h/t CNN]

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