Bats are usually cast in a league with vampires, witches and the supernatural. This is a phenomenon that’s widespread and has been going on for centuries in cultures around the world. In the U.S., some folks credit a certain book with virtually cementing the link between bats and a perception of danger. You know the one: Bram Stoker’s 1897 book Dracula, the first in English literature to link bats to human vampires. Stoker’s antagonist, Count Dracula, who could shape-shift into a bat,¹ caught the public’s imagination and vampire books and movies since have played on the theme that bats are evil, blood-drinking creatures. That’s completely false!
So, let’s dispense with the creepy notion that bats are blood-thirsty predators. In actuality, only three species of bats drink blood and none of these favor human blood. Bats represent a quarter of the mammals on earth, with about 1,200 species, so the population of vampire bats is small. Besides, of the 47 species of bats known to inhabit North America, none are vampire bats (more about them further down the page.)
Inhabiting the U.S. are three small, flower-eating species that spend part of the year in the Southwest, migrating between the U.S. and Mexico, and 44 others spread out across the U.S. that feed on insects. If you have bats patrolling your backyard wildlife habitat at night, count yourself lucky. List of U.S. bat species
The Southwest is home to the greatest diversity of U.S. bats, with Texas hosting more than 30 species. Texas’ Bracken Cave near San Antonio, is home to the largest colony of bats in the world. Twenty million Mexican Free-tailed Bats swoosh out of the cave at dusk and by the time they return at dawn they’ve feasted on 250 tons of insects! Owned by Bat Conservation International, the cave is closed to the public for the protection of the bats, but you can see images and video of the bats leaving the cave here.
The oldest known bat species, Icaronycteris index, lived in the early Eocene Epoch, about 52.2 million years ago. Other fossil evidence points to an ancestor (that’s also shared by humans) dating back 80 million years. As you can see above, bat fossils show a creature not very different from the bats of today.
Myths, be gone with you!
Bats stay quietly hidden by day and come out at night to silently skim the nighttime sky, which makes them mysterious and seem dangerous. But, here are the facts:
- Bats aren’t dangerous. To repeat: Bats aren’t dangerous. They couldn’t be more different from their fictional counterparts. In real life they’re timid, gentle and non-aggressive — so much so, even one with rabies won’t attack.
- Bats aren’t “blind as a bat!” Day and night, their vision is excellent. Researchers have discovered that at least two nocturnal bat species even have color vision.
- Bats aren’t dirty. They’re very clean, spending about a third of their resting time scouring their entire body, much like a cat does.
- Bats don’t get tangled in people’s hair. Most bats are insectivores and it’s true they might occasionally get close to us — even very close — while catching flying insects. But they don’t want to touch us and they see far too well to do it by accident.
- Rabies among bats makes sensational news, but it’s very rare: 1/2 of 1 percent.² Also, rabies is not transmitted through the air; so being near a bat is not a risk.
Major bat groups
Bats belong to the order Chiroptera (ky-ROP-ter-uh). Within this are two major groups — the Microchiroptera and the Megachiroptera. About 200 species are Megachiropterans, known as Old World bats or fruit bats. They’re found only in tropical areas of Europe, Asia and Africa. Some megabats are as small as 2 inches long, but this group also includes the very large “flying foxes,” which are bats with fox-like faces and large eyes. Megabats eat fruit, nectar and pollen. Most don’t use echolocation. Instead, they use their excellent vision and a good sense of smell.
The rest of the bats, Microciropterans, inhabit all areas of the world, except Polar Regions and extreme deserts. These bats use echolocation. Most are insect-eaters, although some species feed on small mammals and fish.
The world’s smallest bat (and possibly smallest mammal) is the bumblebee-sized Kitti’s Hog-nosed Bat, (Craseonycteris thonglongyai), of Thailand and Myanmar, which is only 1-1/8 to 1-1/3 inches long (29 to 33 mm) and weighs just 0.071-ounce (2 g). At the other extreme is the Giant Golden-crowned Flying Fox (Acerodon jubatus), an inhabitant of the Phillipines, which is 7 to 12 inches long (18 to 29 cm), with a wingspan of 5 to 6 feet (1.7 m).
The smallest bat in the U.S. is the Western Pipistrelle (Pipistrellus hesperus), which has a wingspan of 190–215 mm and a body length of 62–80 mm. The largest U.S. bat is the Greater Mastiff Bat (Eumops perotis), 5-1/2 to 7-1/2 inches long (14 to 19 cm), with a wingspan of over 22 inches (56 cm).
The nitty-gritty of vampire bats
Vampire bats are Microbats in the family Phyllostomidae, subfamily Phyllostominae. These bats are small, with a body only about 3 inches long (7.6 cm) and a wingspan of around 8 inches (20 cm). They do drink blood, as their name says, but they seek it from animals like cattle, pigs, horses, birds and sometimes other bats. Occasionally they’ll bite a human who happens to be snoozing uncovered in the great outdoors, but we aren’t their usual target.
Their prey is typically fast asleep when it happens, a bite so tiny with teeth so sharp the victim seldom stirs. The amount of blood loss is so little it doesn’t affect the host, and the bats don’t suck it in, like Count Dracula — they lap it up, about a teaspoonful, over a period of 30 or 40 minutes. Don’t worry yourself with mental images of a vampire bat attacking your big toe if it escapes from under covers while you’re camping– that is, unless you plan to do it in Mexico or Central and South America, where they live.
Vampire bats are smart and can be tamed and trained — National Geographic online reports a researcher who has vampire bats who come when called by their name. Bats are also charitable: Females have been observed feeding new mothers for two weeks after they give birth.
Bats aren’t birds. They’re mammals, the only ones that actually fly rather than glide from a higher elevation to a lower one, such as “flying” squirrels do.
Bats have very different facial features from each other. Some have elongated snouts suitable for sipping nectar in flowers. Others have stubby faces for chewing up fruits. There are bats with pig-like snouts and others with intricate folds and wrinkles on their face that are thought to aid with their echolocation in the dark. Some bats emit sounds through their nose and have a flap of skin called a noseleaf around their nostrils; it’s believed this helps them focus their echolocation. Some of these bats might be considered homely, but others are cute. The flying foxes, for instance, are so-called because of their fox-like faces. (That’s one at the top of this page.)
Ear size and shape varies from small and round to large and pointy. Bats have excellent hearing and many can rotate their ears to gather sound even better. Bat calls can be extremely loud, so to keep from deafening themselves they close their ears when sounding a call.
Their wings have elongated bony structures that work like fingers. On each wing, there’s also a thumb, tipped with a claw that’s used for holding food, climbing and clinging. The name of their order, Chiroptera, is a word that’s from the Greek for “hand-wing.” It’s an appropriate name, isn’t it?
Bat wings move with all the flexibility of hands (and then some), giving them amazing maneuverability in flight. For instance, they can turn 180 degrees in less than half the span of their wings and perform aerobatics that would crash a bird into the ground. Bats have speed, too, able to fly at 35 to 40 miles per hour (48 to 64 km). In at least one instance, even faster: In 2009, scientists attached a transmitter to a Mexican Free-tailed Bat (also called Brazilian Free-tailed Bat) and clocked it at 99 miles per hour (159.3 km/h), a new record for horizontal flight among birds and bats.
The wings are covered by the patagium (puh-TAY-gee-um), a membrane of skin so thin you can see light through it. It appears to be hairless, but with at least some species it’s coated with tiny, inconspicuous hairs thought to play a role in aerodynamics or as sensors. The patagium extends from the tips of the fingers, back along the arm bones to the shoulder and then all the way down the body to the ankle. This membrane also stretches between the legs, but there it’s called the uropatagium or interfemoral membrane. With some species, the uropatagium completely encloses the tail.
Bats’ legs are differently oriented from those of other animals. Indeed, very differently: The knee bends in a backward orientation that enables bats to comfortably hang against a surface, usually head down, without knees getting in the way. Bats hang by their five toes and a system of tendons clench when the weight of their body pulls against them — this allows them to sleep without losing their grip. Weirdly, if a bat dies while roosting, its body will hang there until something knocks it loose. (Birds’ feet also have tendons that hold them in place, but in their case, in an upright position.)
Bats usually have black or brown hair, but there are exceptions. For example, the Northern Yellow Bat (Lasiurus intermedius) is often yellowish; the Silver-haired Bat (Lasionycteris noctivagans) has dark hair tipped with silver, giving it a frosted look; and Eastern Red Bats (Lasiurus borealis) have a reddish-orange coat
The upside to upside-down
You’ve seen photos of bats and they always seem to be hanging upside-down. There’s an anatomical reason for that. It’s because their wings don’t produce enough lift for takeoff from a standstill and they can’t run fast enough to lift themselves into the air. So, bats simply let go from an elevated position and fall into flight. If you were to place a bat on the ground it would walk to the nearest vertical structure and climb it to gain some height before taking wing. Now, that said, it’s going to surprise you that bats don’t always face head-down when they rest.
Bats use vocalizations for communicating with other bats. And, they’re surprisingly complex, at least with Mexican Free-tailed Bats. Dr. George Pollak, a physiologist at the University of Texas in Austin, has been studying the vocalizations of a captive colony of these bats. He describes their vocalizations as made up of syllables and phrases, with “what seems to be some kind of syntax.” He says they’re also “situation-specific.” This complexity probably extends to other bat species, as well. Pollak attributes this to bats’ need to communicate in the dark, where they can’t transmit physical clues. Listen to bats.
Most people know bats can fly in the dark without smacking into things because they use “radar” (electromagnetic radio waves). Well, that’s not entirely accurate. What they use is sonar, which is sound waves. There’s a specific term for sonar use when used in reference to animals — echolocation.
While flying, a bat emits constant high-frequency, short-wavelength sounds which are produced in its larynx and emitted through its mouth (usually) or the nose. The sounds, or calls, are often described as clicks or cheeps, and they can be very loud — up to 120 decibels — louder than a low-flying jet plane. (Fortunately for humans, most of these ultrasonic sounds are beyond our range of hearing.) As the sound waves strike objects in their path, they bounce echoes back to the listening bat, who can interpret them to form a mental picture of what’s ahead. It’s a picture so well-formed, it can detect a single hair or home-in on a mosquito on a moonless night.
The volume, frequency, tone and duration of calls vary depending on the bat’s surroundings. Most are high-frequency sounds we don’t hear, but sometimes calls are made within our hearing. The Western Mastiff bat (Eumops perotis) regularly calls in a lower range. (Listen here to bat sounds captured by ultrasonic recorders)
Not all bats use echolocation. In a bit of evolutionary logic, bats that don’t use it have larger eyes and better vision than those that do. (Bats aren’t the only species that use echolocation. Whales, dolphins, porpoises and certain species of shrews are some of the other animals that do.)
We humans are using rudimentary echolocation when we shout into a canyon and listen to the sound waves as they bounce off the canyon walls. Some blind people use echolocation very successfully in their daily lives, making “clicking” sounds, just as bats do, although at a lower, slower frequency.
The human vampires in literature and movies would have us believe bats burst into flames if caught in sunlight! Of course, they don’t, although they are nocturnal, with the exception of some tropical bats that eat in the daytime. When not feeding, bats “roost,” which just means they find a safe place to groom and rest.
Roosts may be in caves, abandoned mines, rock crevices or under bridges. Also in abandoned buildings, attics, under louvers or siding, and other such places, where they cling to vertical surfaces. Any sliver of an opening is all they need for entry. Some bats roost under loose bark, within hollow trees or clinging to a trunk or even simply hanging from a limb. Where you won’t find them is on any surface which prevents them from falling downward to take flight.
Some bat species are solitary, but most are highly social and roost in colonies of a few up to millions. Males and females of some species stay separated, except during mating season. Other species roost together, except in summer when females form maternal, or nursery, colonies.
Sexual maturity begins at anywhere from eight or nine months old up to two or three years, depending on the species. It usually occurs once or twice a year and the gestation period ranges from about six weeks up to six months or more with some of the fruit bats.
Bats don’t construct nests, even when pregnant. Pregnant females roost together in maternal colonies, sometimes huge ones. At delivery time the mother may separate from the group. Often she turns herself head up and forms a pouch with her interfemoral membrane (uropatagium). She catches her baby in it as he or she emerges.
The “pup” — usually one, occasionally two, rarely four — is born feet first. It’s naked, sightless and a quarter or more the size of its mother. She licks it clean, head to toe. It’s relatively strong, a good thing because it must climb up its mother’s body to suckle. This is a perilous time for the tiny baby — if it loses its hold, the fall could kill it. If it survives, it’ll call out loudly for its mother. She has a strong maternal instinct and will do her best to rescue her pup. She’ll move it to a different location if her roost site is disturbed.
Some bat species carry their pup with them for the first few days while foraging, the baby clinging tightly to its mother’s underside. But as pups put on weight and become too heavy, they’re left in the roost. You may be wondering how the mother can pick her baby out of dozens, hundreds or thousands of other pups packed tightly together. She identifies it through odor and vocal communication. Listen to a young fruit bat calling for attention
Within a week of its birth, the pup will open its eyes; in a couple more, it’ll have fur. It’ll start flying in three to six weeks, and a few months after that, it’ll be completely weaned.
Bats can live 20 to 30 years, but the mortality rate is very high in their first year, from predation, accidents, failure to put on enough fat to last through hibernation, and forced abandonment of young caused by human harassment. All this, combined with bats’ low birth rate, means it takes a very long time for a partially destroyed colony to rebuild itself, if ever.
Most bats are insect eaters, so those living in colder climates hibernate the six or so months of the year when insects aren’t readily available. Their winter quarters (hibernaculum) must be frigid enough to lower their body temperature considerably, but not to the freezing point.
When hibernating, bats allow their temperature to drop to match that of their environment. That dramatically reduces their energy requirements. The resting heart rate slides from over 200 beats per minute down to 12. Breathing slows to perhaps one breath every 45 minutes. They also save energy when they hang by their toes because that doesn’t use muscle.
Before hibernating, bats fatten up so they’ll have enough “fuel” to carry them through to spring. They awaken periodically through the winter to urinate or change position. Each awakening consumes enormous amounts of energy. So, it comes at a high cost when their hibernation site is disturbed. The consequence is death if a bat runs out of stored fat before insects are available. That can easily happen. For example, a Canadian study concluded that each time a Little Brown Bat (Motif lucifugus) is awakened from hibernation it expends 67 days worth of fat!
But, why would waking up consume so much energy? We humans experience a gradual transition to mental alertness when we awaken; it may occur over a period of a few minutes or even seconds. But for bats, coming out of hibernation requires igniting their internal furnace, slowly raising their temperature, increasing their heartbeat and drawing more frequent breaths. It’s a long process — 44 minutes for the Little Brown Bat.
Don’t kill ’em, they’re beneficial
Worldwide about 70 percent of bats eat insects. Some are important predators of crop pests, such as cucumber beetles, while others include nuisance insects, like mosquitoes and gnats, in their diet. Just one bat can devour hundreds of insects an hour — up to 8,000 in a night — often just scooping them into their mouths as they fly. Some bats seek out insects on the ground or trees. Others use their feet to snatch insects. Bats are voracious feeders, eating up to half their body weight each night to meet their energy needs.
Old World bats are important for dispersing seeds, either spitting them out as they eat fruit or eliminating them in their feces. Fruit bats are the most critical factor in reforestation of rainforests — some types of trees owe their continued existence solely to bats. Bat activities also pollinate fruit plants, such as banana, fig, date and mango.
Another benefit of bats is their droppings, called guano, which make an excellent fertilizer. (Note that guano must be collected responsibly, if at all. Hauling it from caves and other bat roosts removes the food source of other creatures living in that ecosystem. Also, too-frequent disruption of resting bats can drive them permanently away.)
Bats, depending on the species, eat beetles, moths, mosquitoes and other insects, as well as nectar and fruit. A few species are carnivorous, feeding on frogs, lizards, birds, small mammals or fish, generally killing them very quickly. Vampire bats feed only on blood.
Bats and rabies
It isn’t true that any bat seen out in the daytime must be rabid. While some species sleep in caves, attics or other dark and hidden resting areas in the daytime, others rest in crevices, under eaves or even hanging from tree limbs, where they might be seen.
Rabies among bats is rare. According to the most recent Rabies Surveillance Report (2015) by the U.S. Centers for Disease Control, across the entire U.S., there were 1,704 confirmed incidents of rabies among bats submitted for testing. Any case of rabies, of course, is one too many, but to put that figure into perspective, consider that there are millions and millions of bats across the country. Bracken Cave alone (near San Antonio, Texas) has 1,500,000 bats. Carlsbad Caverns has 400,000. And, those are just two locations. Of course, a bat should never be touched, unless it needs help. And, even then, never bare-handed. How to humanely remove a bat from a house
Bats are preyed on by numerous animals. Raccoons, snakes, weasels and other predators crawl or reach into places where bats are roosting in the daytime and eat them. Fish catch bats as they’re skimming above water. Hawks and owls snatch bats out of the air when they’re leaving or going to their roosting places at dawn and dusk. Occasionally bats get caught by spiders, such as large tarantulas.
More than half the U.S. species of bats are endangered or threatened, mostly because of human activities: encroachment, harassment, deliberate killing, habitat destruction and wind farms.
¹ Stoker’s Count Dracula could shape-shift into other animals, as well.
² Bat World Sanctuary
* Mariana Fruit Bat juvenile (Pteropus mariannus mariannus), a species of Guam and the Commonwealth of the Northern Mariana Islands. (USFWS-Pacific Region; cc by 2.0)