Why does a vampire bat start peeing while it is still feeding?

To get rid of water so it is light enough to fly

In Carter and Wilkinson’s study, what best predicted whether a bat gave food to a partner?

Whether the partner had fed it before

Where do common vampire bats live in the wild?

Mexico, Central and South America

Vampire Bat

Desmodus rotundus

The common vampire bat (Desmodus rotundus) lives from Mexico to Argentina and Chile. It weighs 15–50 g and feeds only on blood, mostly from livestock such as cattle. It finds warm skin with heat-sensing pits around its nose, makes a tiny cut with its razor-sharp teeth and laps up the blood. Unlike almost every other bat, it can walk, run and jump on the ground. Roost-mates share blood meals with bats that went hungry, and the species is a major carrier of rabies to livestock in Latin America.

Also known as Desmodus rotundus, Common Vampire Bat

Vampire bat abilities

≈30 °C where its heat sensor switches on
Pits around the nose sense the warmth coming off skin, so the bat can find a spot where blood runs close to the surface.
- The sensor is a protein called TRPV1. Its normal version warns of painful heat and switches on at about 40 °C.
- In 2011, Elena Gracheva, David Julius and colleagues showed that the nerves of a vampire bat’s face make a shortened version of TRPV1 that switches on at about 30 °C.
- The rest of its body keeps the normal version, so the bat still feels painful heat.
- Snakes that sense heat, such as pit vipers, use a different protein, TRPA1. Bats and snakes found two separate ways to do the same job.
When does the heat sensor switch on?
Vampire bat’s short TRPV1 (face)≈30 °C
Normal long TRPV1≈40 °C
Measured in lab-grown cells carrying the bat’s two versions of the protein.
Sources [2, 3]
≈3 mm cut
With its razor-sharp front teeth the bat shaves away a tiny patch of skin, so blood can well up, usually without waking the animal.
- Before biting, it finds a warm spot using the heat pits on its nose.
- The central upper incisors remove a small piece of skin, leaving a cut about 3 mm long.
- The bite is described as nearly painless and rarely wakes a sleeping animal.
- The cut is tiny, but bitten cattle can suffer from blood loss, lower milk yields and infected wounds.
Sources [1, 2, 22]
≈20 g of blood a night: two tablespoons
The bat laps the blood with its grooved tongue while chemicals in its saliva stop the wound from clotting.
- A vampire bat needs about two tablespoons of blood (about 20 g) each night.
- Two grooves on the sides of its tongue widen and narrow as it laps.
- Its saliva contains draculin, a protein that blocks two of the blood’s clotting helpers (factors IXa and Xa).
- For a cow, about 14,000 times heavier than the bat, two tablespoons is a very small amount.
Sources [1, 5, 15, 16]
59.5% of its weight in one meal (captive bats)
A meal can weigh more than half as much as the bat, so it gets rid of the water in the blood straight away to stay light enough to fly.
- Captive vampire bats drank an average of 59.5% of their body weight in blood, in 30 minutes or less.
- Their kidneys start making lots of watery pee while they are still feeding. The flow peaks 20–25 minutes after the meal.
- Later, the pee becomes very concentrated, carrying away the waste from all that protein.
- After a big meal, the vampire bat can still jump almost straight up into flight.
One meal compared with the bat
Average meal59.5%
The bat itself100%
Meal weight as a share of body weight, measured in captive bats.
Sources [1, 14]
≈4 km/h running speed on a treadmill
Most bats are clumsy on the ground, but the vampire bat runs with a bounding gallop powered by its folded wings.
- In 2005, Daniel Riskin and John Hermanson put vampire bats on a treadmill. They broke into a run at up to about 4 km/h.
- Its wings are much stronger than its legs, so the front limbs do the pushing. Most running animals push with their back legs.
- Bats lost the ability to run long ago, so vampire bats must have evolved it again on their own.
- Running and hopping help it creep up on a sleeping animal and get away from a kick.
Sources [1, 4, 5]
9.5× its weight, pushed in about 0.03 s
To take off from the ground the bat does a push-up with its wings and springs almost straight up into the air.
- High-speed films show the wings do the pushing, while the hind legs steady and aim the body.
- The push reaches up to 9.5 times the bat’s body weight in about 30 thousandths of a second.
- The bat leaves the ground at about 2.4 m/s, fast enough to open its wings and fly.
- Scientists who measured these jumps describe this vertical take-off as unique among bats.
Sources [1, 6]
8.5× past help beats family ties
A bat that fed well will cough up some blood for a roost-mate that went hungry, and bats that help others get help back.
- In 1984 Gerald Wilkinson showed that wild vampire bats share blood depending both on how related they are and on how much chance they have to pay each other back.
- Gerald Carter and Wilkinson fasted 20 captive bats over two years. How much food a bat had received from a partner predicted how much it gave back 8.5 times better than how related they were.
- Females that had fed more unrelated bats had more donors, and got more food when their usual partner was taken away.
- New friendships start with grooming. Strangers groomed each other more and more before they began to share food.
What predicted who gave food?
Food received before8.5×
Being related1×
From 20 captive bats studied over two years (Carter and Wilkinson, 2013).
Sources [7, 8, 9, 10, 11]
≈2 days without blood before it starts to starve
A small bat burns energy fast and can only store so much, so missing even two nights of food can be deadly.
- A vampire bat can begin to starve after just two days without a meal.
- Bats that fail to feed often get blood from roost-mates, which can keep them alive until the next night.
- This is why sharing matters so much: tonight’s lucky bat may be tomorrow’s hungry one.
- Females do most of the sharing: about 80% of it, according to earlier research.
Sources [8, 13, 16]
20–100 bats in a usual colony
By day vampire bats crowd together in dark caves, hollow trees, wells, mines and old buildings.
- Colonies usually hold 20–100 bats, but up to 5,000 have been reported.
- Roosts smell strongly of ammonia from the digested blood.
- Many roosts are now human-made. In a study in São Paulo state, Brazil, 86% of the roosts mapped were in abandoned houses, manholes and other buildings.
- Bat friendships last: females that groomed and fed each other in captivity kept hanging out together after they were released.
Sources [1, 12, 27]

Tap a pin on the model or a part below.

3 heat-sensing pits around the nose
- Three small pits surround the vampire bat’s fleshy nose pad. Nerves in them react to warmth above about 29 °C.
- That lets the bat feel the heat coming off warm skin, where blood flows close to the surface.
- Among animals with backbones, only vampire bats, boas, pythons and pit vipers are known to sense heat rays (infrared) like this.
Sources [2, 3]
≈3 mm cut in the skin
- The upper front teeth (incisors) and the canines are razor-sharp.
- The big central incisors slice away a tiny patch of skin, making a cut about 3 mm long.
- The bite is described as nearly painless, and it rarely wakes a sleeping animal.
Sources [1, 22]
2 grooves along the sides of the tongue
- The bat does not suck. It laps up the blood with its tongue.
- Two grooves along the sides of the tongue widen and narrow as it feeds, helping move the blood.
- Its saliva contains draculin, a protein that stops the blood from clotting, so the little wound keeps flowing.
Sources [1, 15]
Not blind large eyes for a bat
- The common vampire bat has large eyes and a keen sense of smell.
- It uses both echolocation (calls and their echoes) and vision to find its way and to find animals to feed on.
- Smell and sounds may help it pick out the right animal.
Sources [1]
Long thumb, with soft pads
- Its thumbs are long and well developed.
- On the ground, the thumbs help carry the bat’s weight, like the toes of a front foot.
- During a jump, the thumbs steady the arm and let it push against the ground for longer.
Sources [1, 6]
9.5× its body weight, pushed in one jump
- On the ground the bat folds its wings and walks on its wrists and thumbs.
- Its wings are far stronger than its legs, so the front limbs do most of the pushing when it runs.
- In a take-off jump the wings push down with up to 9.5 times the bat’s weight in about 30 thousandths of a second.
Sources [4, 6]
Hops forwards, backwards and sideways
- Strong hind legs and the long thumbs hold the bat up on the ground.
- In a jump, the hind legs steady the body and aim it over the front limbs, which do the pushing.
- The bat can hop forwards, backwards and sideways to dodge a kicking hoof or a swishing tail.
Sources [1, 6]
0 cm of tail
- The common vampire bat has no tail.
- The skin between its hind legs, which many bats use as a net, is just a narrow fringe.
Sources [1]
59.5% of its weight in one meal (captive bats)
- In a study of captive bats, a meal weighed on average 59.5% of the bat’s own body weight, drunk in 30 minutes or less.
- Blood is mostly water. The bat starts peeing out water while it is still feeding, so it is light enough to fly home.
- An adult weighs 15–50 g.
Sources [1, 14]

Real vampire bats

Photos from Wikimedia Commons: faces, teeth, walking, flying, roosting and sharing food.

Common vampire batGreyish-brown fur, paler below, long thumbs and no tail. 15–50 g. Feeds mostly on mammals, especially livestock.IUCN: Least ConcernUp on its wrists and feet in a roost in Brazil, showing its sharp front teeth. Photo: Charles J. Sharp, CC BY-SA 4.0
Common vampire batGreyish-brown fur, paler below, long thumbs and no tail. 15–50 g. Feeds mostly on mammals, especially livestock.IUCN: Least ConcernWalking position: the folded wings and long thumbs work as front legs. Photo: Uwe Schmidt, CC BY-SA 4.0
In flight: the same wings it walks on spread out into a hand-wingPhoto: Uwe Schmidt, CC BY-SA 4.0
Common vampire batGreyish-brown fur, paler below, long thumbs and no tail. 15–50 g. Feeds mostly on mammals, especially livestock.IUCN: Least ConcernThe bare nose pad: the heat-sensing pits sit in the folds around it. Photo: Carlos Funes, CC BY 4.0
Common vampire batGreyish-brown fur, paler below, long thumbs and no tail. 15–50 g. Feeds mostly on mammals, especially livestock.IUCN: Least ConcernA young male caught near Lamanai, Belize: note the big upper front teeth. Photo: Gerry Carter, CC BY-SA 4.0
A mother and her young: pups stay close to their mothers for monthsPhoto: Uwe Schmidt, CC BY-SA 4.0
Caught on video: one bat passes a blood meal to a roost-matePhoto: Gerry Carter, CC BY-SA 4.0
Two vampire bats hanging in a cave roost in Yucatán, MexicoPhoto: Justin Philbois, CC0
A common vampire bat roosting under the roof of a rural housePhoto: NathDragon, CC BY-SA 4.0
Danger in the roost: a rainbow boa eating a vampire bat in a cave in EcuadorPhoto: Sarah Martin-Solano, Theofilos Toulkeridis, Aaron Addison, Wilmer E. Pozo-Rivera, CC BY 4.0

Vampire bat by the numbers

Measured by scientists and zoos, with comparisons you can picture.

Weight: 15–50 g; head and body 7–9 cm; females usually bigger⁠[1]
One meal: 59.5%; of its body weight, on average, drunk in 30 minutes or less (captive bats)⁠[14]; Meal59.5 %The bat100 %
Blood a night: ≈20 g; about two tablespoons⁠[16]
Without food: ≈2 days; before it can begin to starve⁠[13, 16]
Heat sensor: ≈30 °C; the shortened TRPV1 in its face switches on here; the normal version needs about 40 °C⁠[2]; Face version30.5 °CNormal version39.6 °C
Running speed: ≈4 km/h; on a treadmill, galloping on its wings⁠[5, 4]
Take-off push: 9.5×; its body weight, in about 30 milliseconds; leaves the ground at about 2.4 m/s⁠[6]
Colony size: 20–100; bats; up to 5,000 reported⁠[1]
Young: 1; pup after a pregnancy of about 7 months; newborns weigh 5–7 g⁠[1, 18]
Oldest known: 29 years; in captivity (29.2 years); up to about 12 years in the wild⁠[18, 1]

Vampire bat myths and facts

Tap Myth or Fact for each claim, then check the answer.

0 of 8 answered

“Vampire bats suck blood.”
“Vampire bats live in Transylvania.”
“A vampire bat bite always wakes its victim.”
“Vampire bats can sense heat.”
“Bats can’t walk on the ground.”
“Vampire bats only share food with their family.”
“A vampire bat can drink more than half its weight in one meal.”
“Killing vampire bats stops rabies.”

A life in a vampire bat colony

Vampire bats grow up slowly and can live a long time for such a small mammal.

Before birth
A long pregnancy
A pregnancy lasts about 7 months, very long for a small mammal. Most females have one pregnancy a year.⁠[1, 18]
Birth
One pup
Usually a single pup is born, sometimes twins. A newborn weighs 5–7 g.⁠[1]
First month
Milk only
For its first month the pup drinks only its mother’s milk, and doubles its weight.⁠[1]
Second month
First taste of blood
The mother starts feeding the pup blood she brings back up from her own meal.⁠[1]
About 4 months
Hunting with mum
The young bat goes out on night-time hunts with its mother.⁠[1]
About 9 months
Grown up
Males and females are mature at about 285 days old. Adults groom roost-mates and share blood meals with them.⁠[1, 8]
Up to 12+ years
A long life
Wild vampire bats may live about 12 years. One in captivity reached 29.2 years.⁠[1, 18]

Vampire bats, rabies and cattle

The common vampire bat carries rabies to livestock and sometimes people. Scientists are testing smarter ways to stop it than killing bats.

23
people died in one outbreak
In 2011, 21 school-age children and 2 adults in and around one village in Peru died of rabies passed on by common vampire bats.⁠[22]
6×
more benefit than cost
In Mexico, vaccinating livestock against rabies was worth more than six times what it cost. Killing bats was very unlikely to pay off.⁠[26]
2.6×
more bats protected
Tests with a harmless glowing marker in Peruvian colonies suggest a vaccine gel that bats spread to each other could protect up to 2.6 times more bats than the same effort with a normal vaccine.⁠[24]
86%
roosts in human-made places
In São Paulo state, Brazil, where cattle caught rabies, 86% of the vampire bat roosts mapped were in abandoned houses, manholes and other human-made places.⁠[27]
≈50 km
from the US border
Vampire bats have been found within about 50 km of Texas. Models suggest suitable places may exist in far southern Texas and southern Florida.⁠[25]

Never touch a bat. Anyone bitten or scratched by a bat should see a doctor straight away.

Common vs white-winged vs hairy-legged vampire bat

These are the only three bats that live on blood. All three are found in the Americas.

Common vampire bat vs white-winged vampire bat vs hairy-legged vampire bat
	Common vampire bat	White-winged vampire bat	Hairy-legged vampire bat
Weight⁠[1, 19, 20]	15–50 g	30–45 g	30–40 g
Main food⁠[1, 19, 20]	Blood of mammals, especially livestock	Blood of birds	Blood of birds
Look⁠[1, 19, 20]	Greyish-brown, paler below; long thumbs	Cinnamon-brown; white wing edges; short thumb	Reddish to sooty brown; small ears, short nose, hairy legs
Teeth⁠[19, 20]	20	22	26
Range⁠[1, 19, 20]	Mexico to Argentina and Chile	Mexico and Central America to tropical South America	Southern Texas to eastern Peru and southern Brazil

All three are listed as Least Concern by the IUCN.

Is the common vampire bat endangered?

No. It is common, and cattle ranching has given it more food than ever. The bigger problem is how people try to control it.

IUCN Red List

Least Concern (LC)

Least Concern on the IUCN Red List. Populations have grown where livestock were brought in, because cattle and horses are an easy, plentiful food.⁠[21, 1]

IUCN Red List: Least Concern (Red List version 2022.2)

Threats

Poison and roost destruction
Vampire bats are still culled with poison in Latin America. Fear of vampire bats can also lead people to wreck bat roosts, harming other bat species that need protection.⁠[22, 25]

What’s helping

Vaccinate the cattle6×
In Mexico, vaccinating livestock paid back more than six times its cost.⁠[26]
Vaccines that spread by grooming
Scientists are testing vaccines that bats would spread to each other by touch. Models predict they would work better than culling.⁠[24]
Rethinking culls
A study in Peru found that culling did not reduce rabies in livestock, and reactive culls may have sped up the virus’s spread.⁠[23]

Status of the other vampire bats (IUCN Red List)

White-winged vampire batLeast Concern
Least Concern, but its numbers are poorly known.⁠[19]
Hairy-legged vampire batLeast Concern
Least Concern; the rarest of the three vampire bats.⁠[20]

Vampire bat quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

How does a vampire bat drink blood?

Vampire Bat field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

Vampire bats are unique mammals that exclusively drink blood from sleeping animals, a diet called sanguinivory.

Primary Foods

Cattle blood
Horse blood
Bird blood
Wild mammal blood
Foraging Method: Foraging

Ecological connections

CattleHunts
feeds on their blood at night.
HorseHunts
drinks blood from sleeping horses.
Domestic DogHunts
occasionally feeds on domestic dogs.

Safety

Danger 2/5 · Low

Vampire bats are not found near people, but it's important to stay away from wild animals.

Traits

Collections

Mammals

Classification

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Chiroptera
Family: Phyllostomidae
Genus: Desmodus

Sources for these vampire bat facts

26 studies and references · checked Oct 30, 2026

Frequently Asked Questions

How to identify Vampire Bat?

Compare ears, muzzle, tail, feet and coat markings. Size is hard to judge without something nearby for scale, and young mammals may not have adult coloring yet. Mammal Identifier: upload a photo and compare the visible details.

How long is Vampire Bat?

7-9 cm

What is Vampire Bat's wingspan?

28-35 cm

How much does Vampire Bat weigh?

0.015-0.05 kg

How long does Vampire Bat live?

5-9 years

How fast can Vampire Bat move?

30 km/h

Where is Vampire Bat usually found?

Caves

What does a vampire bat eat?

Only blood. The common vampire bat prefers livestock such as cattle, but also feeds on wild animals and sometimes on people. It needs about two tablespoons (about 20 g) of blood a night.

Do vampire bats suck blood?

No. A vampire bat makes a tiny cut with its razor-sharp front teeth and laps up the blood with its grooved tongue. A protein in its saliva, draculin, stops the blood from clotting.

Do vampire bats bite humans?

Sometimes, especially where people sleep in open houses near bat roosts. Bites on livestock are far more common. Because vampire bats can carry rabies, anyone bitten or scratched by a bat should see a doctor straight away.

How do vampire bats find blood?

They use sight, smell, hearing and echolocation to find an animal, then heat-sensing pits around the nose to find a warm spot where blood flows close under the skin.

Do vampire bats really share food?

Yes. A bat that fed well will bring up some blood for a roost-mate that went hungry. Bats share with relatives and with unrelated friends, and a bat that has helped others in the past gets more help when it needs it.

Can vampire bats walk?

Yes. Unlike most bats, the common vampire bat walks, hops and runs on all fours, using its folded wings and long thumbs as front legs. It can also jump almost straight up into flight.

Are there vampire bats in the United States?

The common vampire bat has been found within about 50 km of Texas, but not in recent times in the US. The hairy-legged vampire bat’s range is listed as reaching southern Texas.

Is the vampire bat endangered?

No. The common vampire bat is listed as Least Concern by the IUCN, and its numbers have grown where livestock were introduced.

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