View source for Biology:Pit viper

{{Short description|Subfamily of snakes}}
{{Automatic taxobox
| image         = 
| image_caption = Timber rattlesnake (''Crotalus horridus''), showing the characteristic infrared pit below and between the eye and nostril
| taxon         = Crotalinae
| authority     = Oppel, 1811
| synonyms      = 
* Crotalini <small>Oppel, 1811</small>
* Crotales <small>Cuvier, 1817</small>
* Crotalidae <small>Gay, 1825</small>
* Crotaloidae <small>Fitzinger, 1826</small>
* Cophiadae <small>Boie, 1827</small>
* Crotaloidei <small>Eichwald, 1831</small>
* Crotalina <small>Bonaparte, 1831</small>
* Bothrophes <small>Fitzinger, 1843</small>
* Crotalinae <small>Cope, 1860</small>
* Teleuraspides <small>Cope, 1871</small>
* Crotalida <small>Strauch, 1873</small>
* Bothrophera <small>Garman, 1884</small>
* Cophiinae <small>Cope, 1895</small>
* Lachesinae <small>Cope, 1900</small>
* Lachesinii <small>Smith, Smith & Sawin, 1977</small>
* Agkistrodontinii <small>Hoge & Romano-Hoge, 1981</small>
* Agkistrodontini <small>Hoge & Romano-Hoge, 1983</small><ref name="McD99">McDiarmid RW, Campbell JA, Touré T (1999). ''Snake Species of the World: A Taxonomic and Geographic Reference, Volume 1''. Washington, District of Columbia: Herpetologists' League. 511 pp. {{ISBN|1-893777-00-6}} (series). {{ISBN|1-893777-01-4}} (volume).</ref>
}}

The '''Crotalinae''', commonly known as '''pit vipers''',<ref name="Meh87">Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. {{ISBN|0-8069-6460-X}}.</ref><ref>Sometimes spelled "pitvipers" – Campbell & Lamar, 2004 {{Page needed|date=June 2011}}</ref>  or '''pit adders''', are a subfamily of [[Biology:Viperidae|viper]]s found in [[Earth:Eurasia|Eurasia]] and the [[Earth:Americas|Americas]]. Like all other vipers, they are venomous. They are distinguished by the presence of a [[Physics:Infrared sensing in snakes|heat-sensing]] pit organ located between the eye and the nostril on both sides of the head. Currently, 23 [[Biology:Genus|genera]] and 155 [[Biology:Species|species]] are recognized:<ref name="ITIS">{{ITIS |id=634394 |taxon=Crotalinae |access-date=26 October 2006}}</ref> These are also the only [[Biology:Viperidae|viperids]] found in the Americas. The groups of snakes represented here include rattlesnakes, [[Biology:Bothrops|lanceheads]], and [[Biology:Trimeresurus|Asian pit vipers]]. The [[Biology:Type genus|type genus]] for this subfamily is ''[[Biology:Crotalus|Crotalus]]'', of which the [[Biology:Type species|type species]] is the [[Biology:Timber rattlesnake|timber rattlesnake]], ''C. horridus''.{{Citation needed|date=June 2011}}

These snakes range in size from the diminutive hump-nosed viper, ''[[Biology:Hypnale hypnale|Hypnale hypnale]]'', that grows to a typical total length (including tail) of only {{convert|30|-|45|cm|in|abbr=on}}, to the bushmaster, ''Lachesis muta'', a species known to reach a maximum total length of {{convert|3.65|m|ft|abbr=on}} 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 pits are the external openings to a pair of extremely sensitive [[Physics:Infrared radiation|infrared]]-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.<ref name="C&L04">Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publishing Associates. 870 pp., 1,500 plates. {{ISBN|0-8014-4141-2}}.</ref> The [[Physics:Infrared sensing in snakes|pit organ]] is complex in structure and is similar to the thermoreceptive labial pits found in [[Biology:Boidae|boa]]s and [[Biology:Pythonidae|python]]s. 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.<ref name="Meh87"/> The membrane has many nerve endings packed with [[Biology:Mitochondria|mitochondria]]. Succinic dehydrogenase, lactic dehydrogenase, [[Chemistry:Adenosine triphosphate|adenosine triphosphate]], [[Biology:Monoamine oxidase|monoamine oxidase]], generalized [[Biology:Esterase|esterase]]s, and acetylcholine esterase have also been found in it.<ref name="C&L04"/> When prey comes into range, infrared radiation falling onto the membrane allows the snake to determine its direction.<ref name="Meh87"/> 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 {{convert|0.2|C-change|F-change}} warmer than the background.<ref name="P&G77">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. {{ISBN|0-8014-1095-9}} (cloth), {{ISBN|0-8014-9164-9}} (paper).</ref> The paired pit organs provide the snake with thermal [[Engineering:Rangefinder|rangefinder]] capabilities.<ref name="B&H05">Bullock, T. H. and Diecke, F. P. J. (1956). Properties of an infrared receptor. Journal of Physiology 134, 47-87.</ref> Clearly, these organs are of great value to a predator that hunts at night, as well as for avoiding the snake’s own predators.<ref name="Sti74">Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. {{ISBN|0-448-11856-4}}.</ref>

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.<ref name="C&L04"/>

==Geographic range==
The subfamily Crotalinae is found from Eastern Europe eastward through Asia to {{wipe|Japan}}, {{wipe|China}}, Indonesia, peninsular {{wipe|India}}, Nepal, and Sri Lanka. In the Americas, they range from southern {{wipe|Canada}} southward to Central America to southern South America.<ref name="McD99"/>

==Habitat==

Crotalines are a versatile subfamily, with members found in habitats ranging from parched [[Earth:Desert|desert]] (e.g., the sidewinder, ''[[Biology:Crotalus cerastes|Crotalus cerastes]]'') to [[Earth:Rainforest|rainforest]]s (e.g., the bushmaster, ''Lachesis muta''). They may be either arboreal or [[Biology:Terrestrial animal|terrestrial]], and at least one species (the cottonmouth, ''[[Biology:Agkistrodon piscivorus|Agkistrodon piscivorus]]'') is semiaquatic. The altitude record is held jointly by ''[[Biology:Crotalus triseriatus|Crotalus triseriatus]]'' in Mexico and ''[[Biology:Gloydius strauchi|Gloydius strauchi]]'' in China, both of which have been found above the treeline at over 4,000 m above sea level.<ref name="C&L04"/>

==Behavior==
Although a few species of crotalines are highly active by day, such as ''[[Biology:Trimeresurus trigonocephalus|Trimeresurus trigonocephalus]]'', a bright green pit viper endemic 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.<ref name="K&B03">{{cite journal |last1=Krochmal |first1=Aaron R. |last2=Bakken |first2=George S. |title=Thermoregulation is the pits: use of thermal radiation for retreat site selection by rattlesnakes |journal=Journal of Experimental Biology |date=1 August 2003 |volume=206 |issue=15 |pages=2539–2545 |doi=10.1242/jeb.00471 |pmid=12819261 |s2cid=18140029 |url=https://journals.biologists.com/jeb/article/206/15/2539/20239/Thermoregulation-is-the-pits-use-of-thermal |access-date=11 June 2022}}</ref>

As ambush predators, crotalines typically wait patiently somewhere for unsuspecting prey to wander by. At least one species, the arboreal ''[[Biology:Gloydius shedaoensis|Gloydius shedaoensis]]'' 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.<ref name="SHI">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. [http://www.bio.usyd.edu.au/Shinelab/old%20labbers/mark/349whydojuvenile.pdf PDF] {{webarchive|url=https://web.archive.org/web/20080724094745/http://www.bio.usyd.edu.au/Shinelab/old%20labbers/mark/349whydojuvenile.pdf |date=24 July 2008 }} at University of Sydney [http://www.bio.usyd.edu.au/ School of Biological Sciences]. Accessed 26 October 2006.</ref>

Many temperate species of pit vipers (e.g. most rattlesnakes) congregate in sheltered areas or "dens" to overwinter (brumate, see [[Biology:Hibernation|hibernation]]), 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,  ''[[Biology:Agkistrodon contortrix|Agkistrodon contortrix]]'', or the Mojave rattlesnake, ''[[Biology:Crotalus scutulatus|Crotalus scutulatus]]''.{{Citation needed|date=June 2011}}

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.{{Citation needed|date=June 2011}}

==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 (egg-laying) pit vipers are ''[[Biology:Lachesis (genus)|Lachesis]]'', ''[[Biology:Calloselasma|Calloselasma]]'', and some ''[[Biology:Trimeresurus|Trimeresurus]]'' species. All egg-laying crotalines are believed to guard their eggs.{{Citation needed|date=June 2011}}

Brood sizes range from two for very small species, to as many as 86 for the fer-de-lance, ''[[Biology:Bothrops atrox|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. <ref>{{Cite journal|last1=Heatwole|first1=H.|first2=Elizabeth|last2=Davison|year=1976|title=A Review of Caudal Luring in Snakes with Notes on Its Occurrence in the Saharan Sand Viper, Cerastes vipera|journal=Herpetologica|volume=32|number=3|pages=332–336
|jstor=3891463|access-date=2021-08-24|url=http://www.jstor.org/stable/3891463}}</ref>

==Taxonomy==
In the past, the pit vipers were usually classed as a separate family: the Crotalidae. Today, however, the [[Biology:Monophyly|monophyly]] of the [[Biology:Viperinae|viperines]] and the crotalines as a whole is undisputed, which is why they are treated here as a subfamily of the [[Biology:Viperidae|Viperidae]].{{Citation needed|date=June 2011}}

==Genera==
{|class="wikitable"
! Genus<ref group=ref name="ITIS">{{ITIS |id=634394 |taxon=Crotalinae |access-date=26 October 2006}}</ref>
! Taxon author<ref group=ref name="ITIS"/>
! Species<ref group=ref name="ITIS"/>
! Common name
! Geographic range<ref group=ref name="McD99">McDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. {{ISBN|1-893777-00-6}} (series). {{ISBN|1-893777-01-4}} (volume).</ref>
|-
|''[[Biology:Agkistrodon|Agkistrodon]]''
|[[Biography:Palisot de Beauvois|Palisot de Beauvois]], 1799
| style="text-align:center;" |6
|style="width:18%"|Moccasins
|style="width:40%"|North America from the northeastern and central USA southward through peninsular Florida and southwestern {{wipe|Texas}}. In Central America on the Atlantic versant from Tamaulipas and Nuevo León southward to the Yucatán Peninsula, Belize and Guatemala. Along the Pacific coastal plain and lower foothills from [[Place:Sonora|Sonora]] south through Guatemala, El Salvador, Honduras and Nicaragua to northwestern Costa Rica.
|-
|''[[Biology:Atropoides|Atropoides]]''
|Werman, 1992
| style="text-align:center;" |1
|Picado's jumping pitviper
|Costa Rica and western Panama
|-
|''[[Biology:Bothriechis|Bothriechis]]''
|Peters, 1859
| style="text-align:center;" |11
|Palm-pitvipers
|Southern Mexico (southeastern Oaxaca and the northern highlands of Chiapas), through Central America to northern South America (Colombia, western Venezuela, Ecuador and northern Peru
|-
|''[[Biology:Bothrocophias|Bothrocophias]]''
|Gutberlet & Campbell, 2001
| style="text-align:center;" |9
|Toadheaded pit vipers
|Northern South America
|-
|''[[Biology:Bothrops|Bothrops]]''
|Wagler, 1824
| style="text-align:center;" |48
|Lanceheads
|Northeastern Mexico (Tamaulipas) southward through Central and South America to {{wipe|Argentina}}; Saint Lucia and Martinique in the Lesser Antilles; Ilha da Queimada Grande off the coast of Brazil
|-
|''[[Biology:Calloselasma|Calloselasma]]''
|Cope, 1860
| style="text-align:center;" |1
|Malayan pitviper
|Southeast Asia from Thailand to northern Malaysia and Java, Indonesia
|-
|''[[Biology:Cerrophidion|Cerrophidion]]''
|Campbell & Lamar, 1992
| style="text-align:center;" |5
|Montane pitvipers
|Southern Mexico (highlands of Guerrero and southeastern Oaxaca), southward through the highlands of Central America (Guatemala, El Salvador, Honduras, northern Nicaragua, Costa Rica) to western Panama
|-
|''[[Biology:Craspedocephalus|Craspedocephalus]]''
|Kuhl & van Hasselt, 1822
| style="text-align:center;" |15
|style="width:18%"|Pit viper
|style="width:40%"|India to Thailand to northern Malaysia and Indonesia
|-
|''[[Biology:Crotalus|Crotalus]]''{{sup|T}}
|[[Biography:Carl Linnaeus|Linnaeus]], [[Biology:10th edition of Systema Naturae|1758]]
| style="text-align:center;" |51
|Rattlesnakes
|The Americas, from southern Canada to northern Argentina
|-
|''[[Biology:Deinagkistrodon|Deinagkistrodon]]''
|Gloyd, 1979
| style="text-align:center;" |1
|Hundred-pace pitviper
|Southeast Asia
|-
|''[[Biology:Garthius|Garthius]]''
|Malhotra & Thorpe, 2004 
| style="text-align:center;" |1
|Mount Kinabalu pit viper, Chasen's mountain pit viper 
|Borneo
|-
|''[[Biology:Gloydius|Gloydius]]''
|Hoge & Romano-Hoge, 1981
| style="text-align:center;" |22
|Asian moccasins
|Russia, east of the Ural Mountains through Siberia, [[Religion:Iran|Iran]], the Himalayas from Pakistan, India, Nepal and China, Korea, Japan and the Ryukyu Islands
|-
|''[[Biology:Hypnale|Hypnale]]''
|Fitzinger, 1843
| style="text-align:center;" |3
|Hump-nosed pit vipers
|Sri Lanka and India
|-
|''[[Biology:Lachesis (genus)|Lachesis]]''
|Daudin, 1803
| style="text-align:center;" |4
|Bushmasters
|Central and South America
|-
|''[[Biology:Metlapilcoatlus|Metlapilcoatlus]]''
|Campbell, Frost, & Castoe, 2019
| style="text-align:center;" |6
|Jumping pitvipers
|The mountains of eastern Mexico southeastward on the Atlantic versant and lowlands though Central America to central Panama. On the Pacific versant, they occur in isolated populations in east-central and southern Mexico, Guatemala, El Salvador, Costa Rica, and Panama.
|-
|''[[Biology:Mixcoatlus|Mixcoatlus]]''
|Jadin, H.M.Smith & Campbell, 2011
| style="text-align:center;" |3
|Mexican pit vipers
|Mexico
|-
|''[[Biology:Ophryacus|Ophryacus]]''
|Cope, 1887
| style="text-align:center;" |3
|Mexican horned pitvipers
|Mexico
|-
|''[[Biology:Ovophis|Ovophis]]''
|Burger, 1981
| style="text-align:center;" |7
|Mountain pit vipers
|Nepal and Seven Sisters (Assam) of India eastward through Myanmar, Cambodia, Thailand, Laos, Vietnam, West Malaysia, Taiwan, Japan (Okinawa) and Indonesia (Sumatra)
|-
|''[[Biology:Porthidium|Porthidium]]''
|Cope, 1871
| style="text-align:center;" |9
|Hognose pit vipers
|Mexico ([[Place:Colima|Colima]], Oaxaca and Chiapas on the Pacific side, the Yucatán Peninsula on the Atlantic side) southward through Central America to northern South America (Ecuador in the Pacific lowlands, northern Venezuela in the Atlantic lowlands)
|-
|''[[Biology:Protobothrops|Protobothrops]]''
|Hoge & Romano-Hoge, 1983 
| style="text-align:center;" |14
|Pit vipers
|Asia
|-
|''[[Biology:Sistrurus|Sistrurus]]''
|Garman, 1883
| style="text-align:center;" |3
|Ground rattlesnakes
|Southeastern Canada, eastern, central and northwestern USA, isolated populations in northern and central Mexico
|-
|''[[Biology:Trimeresurus|Trimeresurus]]''
|Lacépède, 1804
| style="text-align:center;" |43
|Asian lanceheads
|Southeast Asia from India to southern China and Japan, and the [[Place:Malay Archipelago|Malay Archipelago]] to Timor
|-
|''[[Biology:Tropidolaemus|Tropidolaemus]]''
|Wagler, 1830
| style="text-align:center;" |5
|Temple vipers
|Southern India and Southeast Asia
|-
|}
''*) Not including the nominate subspecies.''{{Citation needed|date=June 2011}}<br>
{{sup|T}}) [[Biology:Type genus|Type genus]].<ref group=ref name="McD99" />

{{Reflist|group=ref}}

==See also==
* [[Biology:List of crotaline species and subspecies|List of crotaline species and subspecies]]

==References==
{{Reflist|2}}

==Further reading==
{{Refbegin}}
* 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.&nbsp;901).
* Goris RC (2011). "Infrared organs of snakes: an integral part of vision". ''Journal of Herpetology'' '''45''': 2–14.
{{Refend}}

==External links==

* [http://snakesarelong.blogspot.com/2012/09/snakes-that-can-see-without-eyes.html Pit organs at Life is Short, but Snakes are Long]

{{Taxonbar|from=Q595983}}

[[Category:Crotalinae| ]]

{{Sourceattribution|Pit viper}}