Pit viper

{{Short description|Subfamily of snakes}} {{For|the sunglasses company|Pit Viper (sunglasses)}} {{More citations needed|date=June 2011}} {{Use dmy dates|date=September 2020}} {{Automatic taxobox | fossil_range = {{fossil range|Early Miocene | present}} | image = Timber Rattlesnake by Trisha.jpg | image_caption = [[Timber rattlesnake]] (''Crotalus horridus''), showing the [[loreal pit|characteristic infrared-sensing pit]] below and between the eye and nostril | taxon = Crotalinae | authority = [[Nicolaus Michael Oppel|Oppel]], 1811 | synonyms = {{collapsible list|bullets = true|title=List |Crotalini Oppel, 1811 |Crotales Cuvier, 1817 |Crotalidae Gay, 1825 |Crotaloidae Fitzinger, 1826 |Cophiadae Boie, 1827 |Crotaloidei Eichwald, 1831 |Crotalina Bonaparte, 1831 |Bothrophes Fitzinger, 1843 |Crotalinae Cope, 1860 |Teleuraspides Cope, 1871 |Crotalida Strauch, 1873 |Bothrophera Garman, 1884 |Cophiinae Cope, 1895 |Lachesinae Cope, 1900 |Lachesinii Smith, Smith & Sawin, 1977 |Agkistrodontinii Hoge & Romano-Hoge, 1981 |Agkistrodontini Hoge & Romano-Hoge, 1983<ref name="McD99">[[:fr:Roy Wallace McDiarmid|McDiarmid RW]], [[Jonathan A. Campbell|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 (biology)|subfamily]] of [[Viperidae|viper]]s found in [[Asia]] and the [[Americas]], distinguished by the presence of a pair of [[infrared sensing in snakes|heat-sensing]] organs located in a pit between the [[eye]] and the [[nostril]] on each side of the head. Currently, 23 [[genus|genera]] and 155 species are recognized,<ref name="ITIS">{{ITIS |id=634394 |taxon=Crotalinae |access-date=26 October 2006}}</ref> and like all other vipers, they are [[venomous snake|venomous]]. These are also the only [[Viperidae|viperids]] found in the Americas. The groups of snakes represented here include [[rattlesnake]]s, [[Bothrops|lanceheads]], and [[Trimeresurus|Asian pit vipers]]. The [[type genus]] for this subfamily is ''[[Crotalus]]'', of which the [[type species]] is the [[timber rattlesnake]], ''C. horridus''.{{Citation needed|date=June 2011}}

These snakes range in size from the diminutive hump-nosed viper (''[[Hypnale hypnale]]''), which grows to a typical total length (including tail) of only {{cvt|30|-|45|cm}}; to the bushmaster (''[[Lachesis muta]]''), a species known to reach a maximum total length of {{cvt|3.65|m}} in length.{{citation needed|date=November 2025}}

This viper 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]]s are the external openings to a pair of extremely sensitive [[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 upon.<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>

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"/>

== Evolution == The earliest known fossil pit viper remains are from the [[Early Miocene]] of [[Nebraska]]. As pit vipers are thought to have had an Asian origin before eventually colonizing the Americas, this suggests that they must have originated and diversified even earlier. During the Late Miocene, they reached as far west as eastern Europe, where they are no longer found; it is thought that they did not expand further into Europe.<ref>{{Cite web |title=The first European pit viper from the Miocene of Ukraine - Acta Palaeontologica Polonica |url=https://www.app.pan.pl/article/item/app44-327.html |access-date=2024-02-21 |website=www.app.pan.pl}}</ref>

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

==Habitat== Crotalines are a versatile subfamily, with members found in [[habitat (ecology)|habitats]] ranging from parched [[desert]] (e.g., the sidewinder, ''[[Crotalus cerastes]]'') to [[rainforest]]s (e.g., the bushmaster, ''Lachesis muta''). They may be either [[arboreal]] or [[Terrestrial animal|terrestrial]], and at least one species (the cottonmouth, ''[[Agkistrodon piscivorus]]'') is semiaquatic. The altitude record is held jointly by ''[[Crotalus triseriatus]]'' in Mexico and ''[[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 ''[[Trimeresurus trigonocephalus]]'', a bright green pit viper [[endemic (ecology)|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 |bibcode=2003JExpB.206.2539K |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|url-access=subscription }}</ref>

As ambush predators, crotalines typically wait patiently somewhere for unsuspecting prey to wander by. At least one species, the arboreal ''[[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">[[Richard Shine|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 [[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, ''[[Agkistrodon contortrix]]'', or the Mojave rattlesnake, ''[[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 [[Ovoviviparity|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 ''[[Lachesis (genus)|Lachesis]]'', ''[[Calloselasma]]'', and some ''[[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, ''[[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 (taxonomy)|family]]: the Crotalidae. Today, however, the [[monophyly]] of the [[Viperinae|viperines]] and the crotalines as a whole is undisputed, which is why they are treated here as a subfamily of the [[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> |- |''[[Agkistrodon]]'' |[[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 [[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 [[Sonora]] south through Guatemala, [[El Salvador]], [[Honduras]] and [[Nicaragua]] to northwestern [[Costa Rica]]. |- |''[[Atropoides]]'' |Werman, 1992 | style="text-align:center;" |1 |Picado's jumping pit viper |Costa Rica and western Panama |- |''[[Bothriechis]]'' |[[Wilhelm Peters|Peters]], 1859 | style="text-align:center;" |19 |Palm-pit vipers |Southern Mexico (southeastern [[Oaxaca]] and the northern highlands of [[Chiapas]]), through Central America to northern South America ([[Colombia]], western [[Venezuela]], [[Ecuador]] and northern [[Peru]] |- |''[[Bothrocophias]]'' |[[Ronald L. Gutberlet Jr.|Gutberlet]] & [[Jonathan A. Campbell|Campbell]], 2001 | style="text-align:center;" |9 |Toadheaded pit vipers |Northern South America |- |''[[Bothrops]]'' |[[Johann Georg Wagler|Wagler]], 1824 | style="text-align:center;" |48 |Lanceheads |Northeastern Mexico (Tamaulipas) southward through Central and South America to [[Argentina]]; [[Saint Lucia]] and [[Martinique]] in the [[Lesser Antilles]]; [[Ilha da Queimada Grande]] off the coast of Brazil |- |''[[Calloselasma]]'' |[[Edward Drinker Cope|Cope]], 1860 | style="text-align:center;" |1 |Malayan pit viper |Southeast Asia from [[Thailand]] to northern [[Malaysia]] and [[Java]], [[Indonesia]] |- |''[[Cerrophidion]]'' |Campbell & Lamar, 1992 | style="text-align:center;" |5 |Montane pit vipers |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 |- |''[[Craspedocephalus]]'' |[[Heinrich Kuhl| Kuhl]] & [[Johan Conrad van Hasselt|van Hasselt]], 1822 | style="text-align:center;" |15 |style="width:18%"|Pit viper |style="width:40%"|India to [[Thailand]] to northern [[Malaysia]] and [[Indonesia]] |- |''[[Crotalus]]''{{sup|T}} |[[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]] | style="text-align:center;" |51 |Rattlesnakes |The Americas, from southern Canada to northern Argentina |- |''[[Deinagkistrodon]]'' |[[Howard K. Gloyd|Gloyd]], 1979 | style="text-align:center;" |1 |Hundred-pace pit viper |Southeast Asia |- |''[[Garthius]]'' |Malhotra & Thorpe, 2004 | style="text-align:center;" |1 |Mount Kinabalu pit viper, Chasen's mountain pit viper |[[Borneo]] |- |''[[Gloydius]]'' |Hoge & Romano-Hoge, 1981 | style="text-align:center;" |22 |Asian moccasins |Russia, east of the [[Ural Mountains]] through [[Siberia]], [[Iran]], the [[Himalayas]] from Pakistan, India, [[Nepal]] and China, Korea, Japan and the [[Ryukyu Islands]] |- |''[[Hypnale]]'' |[[Leopold Fitzinger|Fitzinger]], 1843 | style="text-align:center;" |3 |Hump-nosed pit vipers |[[Sri Lanka]] and India |- |''[[Lachesis (genus)|Lachesis]]'' |[[François Marie Daudin|Daudin]], 1803 | style="text-align:center;" |4 |Bushmasters |Central and South America |- |''[[Metlapilcoatlus]]'' |Campbell, Frost, & Castoe, 2019 | style="text-align:center;" |6 |Jumping pit vipers |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. |- |''[[Mixcoatlus]]'' |Jadin, H.M.Smith & Campbell, 2011 | style="text-align:center;" |3 |Mexican pit vipers |Mexico |- |''[[Ophryacus]]'' |[[Edward Drinker Cope|Cope]], 1887 | style="text-align:center;" |3 |Mexican horned pit vipers |Mexico |- |''[[Ovophis]]'' |Burger, 1981 | style="text-align:center;" |8<ref>{{Cite web |date=2026-03-24 |title=Flying snake, pit viper among rare and new species discovered in cave in Cambodia - CBS News |url=https://www.cbsnews.com/news/flying-snake-pit-viper-rare-new-species-discovered-cambodia-cave-report/ |access-date=2026-03-24 |website=www.cbsnews.com |language=en-US}}</ref> |Mountain pit vipers |Nepal and [[Seven Sister States|Seven Sisters]] ([[Assam]]) of India eastward through [[Myanmar]], [[Cambodia]], Thailand, [[Laos]], [[Vietnam]], [[West Malaysia]], [[Taiwan]], Japan ([[Okinawa Prefecture|Okinawa]]) and Indonesia ([[Sumatra]]) |- |''[[Porthidium]]'' |[[Edward Drinker Cope|Cope]], 1871 | style="text-align:center;" |9 |Hognose pit vipers |Mexico ([[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) |- |''[[Protobothrops]]'' |Hoge & Romano-Hoge, 1983 | style="text-align:center;" |14 |Pit vipers |Asia |- |''[[Sistrurus]]'' |[[Samuel Garman|Garman]], 1883 | style="text-align:center;" |3 |Ground rattlesnakes |Southeastern Canada, eastern, central and northwestern USA, isolated populations in northern and central Mexico |- |''[[Trimeresurus]]'' |[[Bernard Germain de Lacépède|Lacépède]], 1804 | style="text-align:center;" |43 |Asian lanceheads |Southeast Asia from India to southern China and Japan, and the [[Malay Archipelago]] to [[Timor]] |- |''[[Tropidolaemus]]'' |[[Johann Georg Wagler|Wagler]], 1830 | style="text-align:center;" |5 |Temple vipers |Southern India and Southeast Asia |- |} ''*) Not including the nominate subspecies.''{{Citation needed|date=June 2011}} {{sup|T}}) [[Type genus]].<ref group=ref name="McD99" />

==See also== * [[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. * [[Albert Hazen Wright|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. {{Refend}}

==External links== {{Commons category|Crotalinae}} {{Wikispecies|Crotalinae}}

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

[[Category:Pit vipers| ]]