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Vampire bat

Vampire bat

Overview
Vampire bats are bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...

s whose food source is blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

, a dietary trait called hematophagy
Hematophagy
Hematophagy is the practice of certain animals of feeding on blood...

. There are three bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...

 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 that feed solely on blood: the Common Vampire Bat
Common Vampire Bat
The Common Vampire Bat is a small leaf-nosed bat native to the Americas. It is one of three extant species of vampire bat, the other two being the Hairy-legged Vampire Bat and the White-winged Vampire Bat. Along with them, it is the only parasitic mammal. It mainly feeds on the blood of livestock...

 (Desmodus rotundus), the Hairy-legged Vampire Bat
Hairy-legged Vampire Bat
The Hairy-legged Vampire Bat is one of three species of vampire bat. Despite connotations of vampires, it mainly feeds on the blood of birds. This vampire bat lives mainly in tropical and subtropical forestlands of South America...

 (Diphylla ecaudata), and the White-winged Vampire Bat
White-winged Vampire Bat
The White-winged Vampire Bat is a species of vampire bat. It is the only member of the genus Diaemus. It is found from Mexico to southern Argentina and is present on the islands of Trinidad and Isla Margarita...

 (Diaemus youngi).
All three species are native to the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

, ranging from Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 to Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

, and Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

.

Due to differences between the three species, they have each been placed within a different genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

, each consisting of one species.
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Encyclopedia
Vampire bats are bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...

s whose food source is blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

, a dietary trait called hematophagy
Hematophagy
Hematophagy is the practice of certain animals of feeding on blood...

. There are three bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...

 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 that feed solely on blood: the Common Vampire Bat
Common Vampire Bat
The Common Vampire Bat is a small leaf-nosed bat native to the Americas. It is one of three extant species of vampire bat, the other two being the Hairy-legged Vampire Bat and the White-winged Vampire Bat. Along with them, it is the only parasitic mammal. It mainly feeds on the blood of livestock...

 (Desmodus rotundus), the Hairy-legged Vampire Bat
Hairy-legged Vampire Bat
The Hairy-legged Vampire Bat is one of three species of vampire bat. Despite connotations of vampires, it mainly feeds on the blood of birds. This vampire bat lives mainly in tropical and subtropical forestlands of South America...

 (Diphylla ecaudata), and the White-winged Vampire Bat
White-winged Vampire Bat
The White-winged Vampire Bat is a species of vampire bat. It is the only member of the genus Diaemus. It is found from Mexico to southern Argentina and is present on the islands of Trinidad and Isla Margarita...

 (Diaemus youngi).
All three species are native to the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...

, ranging from Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 to Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

, and Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

.

Species


Due to differences between the three species, they have each been placed within a different genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

, each consisting of one species. In the older literature
Literature
Literature is the art of written works, and is not bound to published sources...

, these three genera were placed within a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of their own, Desmodontidae, but taxonomist
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

s have now grouped them as a subfamily, the Desmodontinae, in the American leaf-nosed bat family, Phyllostomidae.

The fact that the three known species of vampire bat all seem more similar to one another than to any other species suggests that sanguivorous habits (feeding on blood) evolved only once, and that the three species may share a common ancestor.

Anatomy



Unlike fruit-eating bats, the vampire bat has a short, conical muzzle. It also lacks a nose leaf, instead having naked pads with U-shaped grooves at the tip. The common vampire bat also has specialized thermoreceptors on its nose, which aids the animal in locating areas where the blood flows close to the skin of its prey. A nucleus has been found in the brain of vampire bats that has a similar position and similar histology to the infrared receptor
Infrared sensing in snakes
The ability to sense infrared thermal radiation evolved independently in several different families of snakes. Essentially, it allows these animals to “see” radiant heat at wavelengths between 5 and 30 μm to a degree of accuracy such that a blind rattlesnake can target vulnerable body parts of the...

 of infrared-sensing snakes.

Vampire bats generally have small ears and a short tail . Their front teeth are specialized for cutting and their back teeth are much smaller than in other bats. The inferior colliculus
Inferior colliculus
The inferior colliculus is the principal midbrain nucleus of the auditory pathway and receives input from several more peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex...

, part of the bat's brain that processes sound, is well adapted to detecting the regular breathing sounds of sleeping animals that serve as their main food source.

While other bats have almost lost the ability to maneuver on land, Vampire bats can also run by using a unique bounding gait, in which the forelimbs instead of the hindlimbs are recruited for force production as the wings are much more powerful than the legs. This ability to run seems to have evolved independently within the bat lineage.

Vampire bats use infrared radiation to locate blood hotspots on their prey, according to a study published in Nature. The infrared signals are received through the bat's three 1mm-diameter leaf pits, which are located around their noses and can change direction when needed. The only other vertebrates capable of detecting infrared radiation are boas, pythons and pit vipers, all of which have pit organs. A mass of nerve cells called trigeminal ganglia (TG) - which are associated with the trigeminal nerves responsible for causing sensations in the face - stimulate the leaf pits. The TG of vampire bats have large diameter neurons, similar to those of pit-bearing snakes, while fruit bats have a much smaller trigeminal ganglia.

Ecology and lifecycle


Vampire bats tend to live in colonies in almost completely dark places, such as caves, old wells, hollow trees, and buildings. They range in Central to South America and live in arid to humid, tropical and sub tropical areas. Vampire bats live in colonies that can number in the thousands in roosting sites. The basic social structure of roosting bats is made of harems which are composed of females and their offspring and a few adult males, known as "resident males" and a separate group of males, known as "non-resident males". In hairy legged vampire bats, the hierarchical segregation of non-resident males is less strict than in common vampire bats. Non-resident males are accepted into the harems when the ambient temperature lowers. This behavior suggests social thermoregulation.

Resident males mate with the females in their harems, however it is common for outside males to copulate with the females. Female offspring usually remain in their natal groups unless their mothers die or move. Several matrilines can be found in a group as unrelated females regularly join groups. Male offspring tend to live in their natal groups until they are about two years old, sometimes being forcefully expelled by the resident adult males.

Vampire bats are believed to be the only species of bats in the world to "adopt" another young bat if something happens to the bat's mother. Vampire bats also share a strong family bond with members of the colony, which is believed to be why they are the only bats to take up this adoption characteristic. Another unique adaptation of vampire bats is the sharing of food. A vampire bat can only survive about two days without a meal of blood, yet they cannot be guaranteed of finding food every night. This poses a problem, so when a bat fails to find food it will often "beg" another bat for food. The "host" bat may regurgitate a small amount of blood to sustain the other member of the colony. This has been noted by many naturalists as an example of reciprocal altruism in nature. Vampire bats also engage in social grooming. It usually occurs between females and their offspring, but it is also significant between adult females. Social grooming is mostly associated with food sharing.

Feeding



Vampire bats hunt only when it is fully dark. Like fruit-eating bats, and unlike insectivorous and fish-eating bats, they emit only low-energy sound pulses. The common vampire bat feeds mostly on the blood of mammals (including humans), whereas both the hairy-legged vampire bat and white-winged vampire bat feed on the blood of birds. Once the common vampire bat locates a host, such as a sleeping mammal, it lands and approaches it on the ground. It then likely uses thermoception
Thermoception
Thermoception or thermoreception is the sense by which an organism perceives temperature. The details of how temperature receptors work are still being investigated. Ciliopathy is associated with decreased ability to sense heat, thus cilia may aid in the process...

 to identify a good spot on the skin to bite.

Vampire bats are very agile and a recent study found that common vampire bats can, in addition to walk, run at speeds of up to 7.9 km per hour (4.9 miles per hour). They locate a suitable place to bite using their infrared sensors. They then create a small incision with their teeth and lap up blood from the wound.

As noted by Arthur M. Greenhall:If there is fur on the skin of the host, the common vampire bat uses its canine
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...

 and cheek teeth like a barber's blades to shave away the hairs. The bat's razor-sharp upper incisor teeth
Maxillary central incisor
The maxillary central incisor is a human tooth in the front upper jaw, or maxilla, and is usually the most visible of all teeth in the mouth. It is located mesial to the maxillary lateral incisor. As with all incisors, their function is for shearing or cutting food during mastication . There are...

 then make a 7mm long and 8mm deep cut. The upper incisors lack enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...

, which keeps them permanently razor sharp.

The bat’s saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

, which is injected into the victim, has a key function in feeding from the wound. The saliva contains several compounds that prolong bleeding, such as anticoagulant
Anticoagulant
An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...

s that inhibit blood clotting, and compounds that prevent the constriction of blood vessels near the wound.

Digestion


A typical female vampire bat weighs 40 grams and can consume over 20 grams (1 fluid ounce) of blood in a 20-minute feed. This feeding behaviour is facilitated by its anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

 and physiology for rapid processing and digestion of the blood to enable the animal to take flight soon after the feeding.

The stomach lining rapidly absorbs the blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

, which is quickly transported to the kidneys from where it passes to the bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...

 for excretion. A common vampire bat begins to expel urine within two minutes of feeding.

While shedding much of the blood's liquid makes taking off from the ground easier, the bat still has added almost 20-30% of its body weight in blood. To take off from the ground, the bat generates extra lift by crouching and flinging itself into the air. Typically within two hours of setting out, the common vampire bat returns to its roost and settles down to spend the rest of the night digesting its meal. Excess urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....

 from protein is thereby excreted via the urinary system of the vampire bat aided by hormones to make concentrated urine that consists of concentrated urea in small amounts of water.

Human health



Only 0.5% of bats carry rabies. However, of the few cases of rabies
Rabies
Rabies is a viral disease that causes acute encephalitis in warm-blooded animals. It is zoonotic , most commonly by a bite from an infected animal. For a human, rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms...

 reported in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 every year, most are caused by bat bites.
The highest occurrence of rabies in vampire bats occurs in the large populations found in South America. However, there is less risk of infection to the human population than to livestock exposed to bat bites.

Although most bats do not have rabies, those that do may be clumsy, disoriented, and unable to fly, which makes it more likely that they will come into contact with humans.

The unique properties of the vampire bats' saliva have found some positive use in medicine. A study which appeared in the January 10, 2003 issue of Stroke: Journal of the American Heart Association, tested a genetically engineered drug called desmoteplase
Desmoteplase
Desmoteplase is a novel, highly fibrin-specific thrombolytic agent in phase III of clinical development. In 2009, 2 large trials were started, and the results of these studies will determine whether desmoteplase will gain marketing authorization as a safe and effective treatment for patients with...

, which uses the anticoagulant
Anticoagulant
An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...

 properties of the saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...

 of Desmodus rotundus, and was shown to increase blood flow in stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

 patients.

Role in fiction



The vampire bat is often used in movies and books about vampire
Vampire
Vampires are mythological or folkloric beings who subsist by feeding on the life essence of living creatures, regardless of whether they are undead or a living person...

s. Fictional vampires also consume blood, usually in order to survive. Comparable to the actual vampire bat, the most common feeding method is piercing a hole in the victim's neck with sharp fangs and sucking blood from the pierced area. Fictional vampires are also commonly nocturnal, and rarely come out during the day, similar to vampire bats. Other attributes of fictional vampires include, but are not restricted to, the ability to transform into a vampire bat and animal-like senses of sight and hearing. In several vampire horror films a vampire bat arrives through the victim's window then magically transforms into the fictional mythological creature.

Further reading


  • Greenhall, Arthur M. 1961. Bats in Agriculture. A Ministry of Agriculture Publication. Trinidad and Tobago.
  • Greenhall, Arthur M. 1965. The Feeding Habits of Trinidad Vampire Bats.
  • Greenhall, A., G. Joermann, U. Schmidt, M. Seidel. 1983. Mammalian Species: Desmodus rotundus. American Society of Mammalogists, 202: 1-6.
  • A.M. Greenhall and U. Schmidt, editors. 1988. Natural History of Vampire Bats, CRC Press, Boca Raton, Florida. ISBN 0849367506; ISBN 978-0849367502
  • Pawan, J.L. (1936b). "Rabies in the Vampire Bat of Trinidad with Special Reference to the Clinical Course and the Latency of Infection." Annals of Tropical Medicine and Parisitology. Vol. 30, No. 4. December, 1936.

External links