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The Crotalinae, commonly known as pit vipers,Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. . crotaline snakes (from grc, κρόταλον ''krotalon'' castanet), or pit adders, are a
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus Genus ( plural genera ) is a taxonomic rank used in the biological classifica ...
of vipers found in
Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelag ...
and the
Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North America, North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. ...
. Like all other vipers, they are venomous. They are distinguished by the presence of a heat-sensing pit organ located between the eye and the nostril on both sides of the head. Currently, 23
genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
and 155
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
are recognized: These are also the only
viperids The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fang ...
found in the Americas. The groups of snakes represented here include
rattlesnake Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small an ...
s, lanceheads, and Asian pit vipers. The type genus for this subfamily is '' Crotalus'', of which the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...
is the timber rattlesnake, ''C. horridus''. These snakes range in size from the diminutive hump-nosed viper, ''
Hypnale hypnale ''Hypnale hypnale'' is a venomous pit viper species endemic to India and Sri Lanka. Common names include the hump-nosed viper,United States Navy (1991). ''Poisonous Snakes of the World''. New York: United States Government/Dover Publications In ...
'', that grows to a typical total length (including tail) of only , to the bushmaster, '' Lachesis muta'', a species known to reach a maximum total length of in length. This subfamily is unique in that all member species share a common characteristic – a deep pit, or fossa, in the loreal area between the eye and the nostril on either side of the head. These
loreal pit The loreal pit is the deep depression, or fossa, in the loreal area on either side of the head in pit vipers (crotaline snakes). The area is located behind the nostril and in front of the eye, but below the line that runs between the centers of ...
s are the external openings to a pair of extremely sensitive
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
-detecting organs, which in effect give the snakes a sixth sense to help them find and perhaps even judge the size of the small, warm-blooded prey on which they feed.Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publishing Associates. 870 pp., 1,500 plates. . The
pit organ The ability to sense infrared thermal radiation evolved independently in two different groups of snakes, one consisting of the families Boidae (boas) and Pythonidae (pythons), the other of the family Crotalinae (pit vipers). What is commonly calle ...
is complex in structure and is similar to the thermoreceptive labial pits found in boas and pythons. It is deep and located in a maxillary cavity. The membrane is like an eardrum that divides the pit into two sections of unequal size, with the larger of the two facing forwards and exposed to the environment. The two sections are connected via a narrow tube, or duct, that can be opened or closed by a group of surrounding muscles. By controlling this tube, the snake can balance the air pressure on either side of the membrane. The membrane has many nerve endings packed with
mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...
. Succinic dehydrogenase, lactic dehydrogenase,
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms ...
, monoamine oxidase, generalized esterases, and acetylcholine esterase have also been found in it. When prey comes into range, infrared radiation falling onto the membrane allows the snake to determine its direction. Having one of these organs on either side of the head produces a stereo effect that indicates distance, as well as direction. Experiments have shown, when deprived of their senses of sight and smell, these snakes can strike accurately at moving objects less than warmer than the background.Parker HW, Grandison AGC. 1977. Snakes -- a natural history. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. (cloth), (paper). The paired pit organs provide the snake with thermal rangefinder capabilities.Bullock, T. H. and Diecke, F. P. J. (1956). Properties of an infrared receptor. Journal of Physiology 134, 47-87. Clearly, these organs are of great value to a predator that hunts at night, as well as for avoiding the snake’s own predators.Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. . Among vipers, these snakes are also unique in that they have a specialized muscle, called the muscularis pterigoidius glandulae, between the venom gland and the head of the ectopterygoid. Contraction of this muscle, together with that of the muscularis compressor glandulae, forces venom out of the gland.


Geographic range

The subfamily Crotalinae is found in the Old World from Eastern Europe eastward through Asia to
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
, peninsular
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
,
Nepal Nepal (; ne, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in South Asia. It is ma ...
, and
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
. In the Americas, they range from southern
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
southward to Central America to southern South America.


Habitat

Crotalines are a versatile subfamily, with members found in
habitats In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
ranging from parched
desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
(e.g., the sidewinder, '' Crotalus cerastes'') to
rainforest Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainfores ...
s (e.g., the bushmaster, ''Lachesis muta''). They may be either arboreal or terrestrial, and at least one species (the cottonmouth, ''
Agkistrodon piscivorus ''Agkistrodon piscivorus'' is a species of pit viper in the subfamily Crotalinae of the family Viperidae. It is one of the world's few semiaquatic vipers (along with the Florida cottonmouth), and is native to the southeastern United States. As ...
'') is semiaquatic. The altitude record is held jointly by '' Crotalus triseriatus'' in Mexico and ''
Gloydius strauchi :''Common names: Tibetan pit viper, Gloyd HK, Conant R (1990). ''Snakes of the'' Agkistrodon ''Complex: A Monographic Review''. Society for the Study of Amphibians and Reptiles. 614 pp. 52 plates. LCCN 89-50342. . Strauch's pitviper. Gumprecht A ...
'' in China, both of which have been found above the treeline at over 4,000 m above sea level.


Behavior

Although a few species of crotalines are highly active by day, such as ''
Trimeresurus trigonocephalus ''Craspedocephalus trigonocephalus'', the Sri Lankan pit viper, Ceylon pit viper, Sri Lankan green pitviper or locally, pala polonga, ( si, පළා පොළඟා) is a venomous pit viper species endemic to Sri Lanka. No subspecies are current ...
'', a bright green pit viper
endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
to Sri Lanka, most are nocturnal, preferring to avoid high daytime temperatures and to hunt when their favored prey are also active. The snakes' heat-sensitive pits are also thought to aid in locating cooler areas in which to rest. As ambush predators, crotalines typically wait patiently somewhere for unsuspecting prey to wander by. At least one species, the arboreal ''
Gloydius shedaoensis :''Common names: Shedao island pitviper,Gumprecht A, Tillack F, Orlov NL, Captain A, Ryabov S. 2004. ''Asian Pitvipers''. GeitjeBooks. Berlin. 1st Edition. 368 pp. . Shedao pit-viper.Shine R, Sun L, Kearney M, Fitzgerald M. 2002. Why do Juvenile ...
'' of China, is known to select a specific ambush site and return to it every year in time for the spring migration of birds. Studies have indicated these snakes learn to improve their strike accuracy over time. Shine R, Sun L, Kearney M, Fitzgerald M (2002). "Why do Juvenile Chinese Pit-Vipers (''Gloydius shedoaensis'') Select Arboreal Ambush Sites?" ''Ethology'' 108: 897–910. ISSN 0179-1613
PDF
at University of Sydne
School of Biological Sciences
Accessed 26 October 2006.
Many temperate species of pit vipers (e.g. most rattlesnakes) congregate in sheltered areas or "dens" to overwinter (brumate, see
hibernation Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It mos ...
), the snakes benefiting from the combined heat. In cool temperatures and while pregnant, pit vipers also bask on sunny ledges. Some species do not mass together in this way, for example the copperhead, ''
Agkistrodon contortrix The eastern copperhead (''Agkistrodon contortrix''), also known as the copperhead, is a species of venomous snake, a pit viper, endemic to eastern North America; it is a member of the subfamily Crotalinae in the family Viperidae. The eastern co ...
'', or the Mojave rattlesnake, '' Crotalus scutulatus''. Like most snakes, crotalines keep to themselves and strike only if cornered or threatened. Smaller snakes are less likely to stand their ground than larger specimens. Pollution and the destruction of rainforests have caused many pit viper populations to decline. Humans also threaten pit vipers, as many are hunted for their skins or killed by cars when they wander onto roads.


Reproduction

With few exceptions, crotalines are ovoviviparous, meaning that the embryos develop within eggs that remain inside the mother's body until the offspring are ready to hatch, when the hatchlings emerge as functionally free-living young. In such species, the eggshells are reduced to soft membranes that the young shed, either within the reproductive tract, or immediately after emerging. Among the
oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and m ...
(egg-laying) pit vipers are '' Lachesis'', ''
Calloselasma :''Common names: Malayan ground pit viper, Malayan pit viper, Malayan ground snake, Malayan moccasin. ''Calloselasma'' is a monotypic genus created for a venomous pit viper species, ''C. rhodostoma'', which is endemic to Southeast Asia from Thai ...
'', and some '' Trimeresurus'' species. All egg-laying crotalines are believed to guard their eggs. Brood sizes range from two for very small species, to as many as 86 for the fer-de-lance, '' Bothrops atrox'', which is among the most prolific of all live-bearing snakes. Many young crotalines have brightly coloured tails that contrast dramatically with the rest of their bodies. These tails are known to be used by a number of species in a behavior known as caudal luring; the young snakes make worm-like movements with their tails to lure unsuspecting prey within striking distance.


Taxonomy

In the past, the pit vipers were usually classed as a separate
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
: the Crotalidae. Today, however, the
monophyly In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic ...
of the viperines and the crotalines as a whole is undisputed, which is why they are treated here as a subfamily of the
Viperidae The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs th ...
.


Genera

''*) Not including the nominate subspecies.''
) Type genus.


See also

*
List of crotaline species and subspecies This is a list of all sure genera, species and subspecies of the subfamily Crotalinae, otherwise referred to as crotalines, pit vipers, or pitvipers, and including rattlesnakes ''Crotalus'' and ''Sistrurus''. This list follows the taxonomy as of ...


References


Further reading

* Gumprecht, Andreas; Tillack, Frank (2004). "A proposal for a replacement name of the snake genus ''Ermia'' Zhang, 1993". ''Russian Journal of Herpetology'' 11: 73–76. * Wright, Albert Hazen; Wright, Anna Allen (1957). ''Handbook of Snakes of the United States and Canada''. Ithaca and London: Comstock Publishing Associates, a Division of Cornell University Press. 1,105 pp. (in two volumes). (Seventh Printing 1985). ("Crotalidae", p. 901). * Goris RC (2011). "Infrared organs of snakes: an integral part of vision". ''Journal of Herpetology'' 45: 2–14.


External links


Pit organs at Life is Short, but Snakes are Long
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