Pit viper

Pit viper; Temporal range:Early Miocene–present PreꞒ Ꞓ O S D C P T J K Pg N
	Timber rattlesnake(Crotalus horridus), showing the characteristic infrared pit below and between the eye and nostril
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Viperidae
Subfamily:	Crotalinae; Oppel,1811
Synonyms
	List CrotaliniOppel, 1811 ; CrotalesCuvier, 1817 ; CrotalidaeGay, 1825 ; CrotaloidaeFitzinger, 1826 ; CophiadaeBoie, 1827 ; CrotaloideiEichwald, 1831 ; CrotalinaBonaparte, 1831 ; BothrophesFitzinger, 1843 ; CrotalinaeCope, 1860 ; TeleuraspidesCope, 1871 ; CrotalidaStrauch, 1873 ; BothropheraGarman, 1884 ; CophiinaeCope, 1895 ; LachesinaeCope, 1900 ; LachesiniiSmith, Smith & Sawin, 1977 ; AgkistrodontiniiHoge & Romano-Hoge, 1981 ; AgkistrodontiniHoge & Romano-Hoge, 1983 ;

TheCrotalinae,commonly known aspit vipers,^[2]^[3]orpit adders,are asubfamilyofvipersfound in Asia and the Americas. Like all other vipers, they arevenomous.They are distinguished by the presence of aheat-sensingpit organ located between the eye and the nostril on both sides of the head. Currently, 23generaand 155 species are recognized:^[4]These are also the onlyviperidsfound in the Americas. The groups of snakes represented here includerattlesnakes,lanceheads,andAsian pit vipers.Thetype genusfor this subfamily isCrotalus,of which thetype speciesis thetimber rattlesnake,C. horridus.^{[citation needed]}

These snakes range in size from the diminutive hump-nosed viper,Hypnale hypnale,that grows to a typical total length (including tail) of only 30–45 cm (12–18 in), to the bushmaster,Lachesis muta,a species known to reach a maximum total length of 3.65 m (12.0 ft) 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. Theseloreal pitsare the external openings to a pair of extremely sensitiveinfrared-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.^[5]Thepit organis complex in structure and is similar to the thermoreceptive labial pits found inboasandPython 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.^[2]The membrane has many nerve endings packed withmitochondria.Succinic dehydrogenase, lactic dehydrogenase,adenosine triphosphate,monoamine oxidase,generalizedesterases,andacetylcholine esterasehave also been found in it.^[5]When prey comes into range, infrared radiation falling onto the membrane allows the snake to determine its direction.^[2]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 0.2 °C (0.36 °F) warmer than the background.^[6]The paired pit organs provide the snake with thermalrangefindercapabilities.^[7]Clearly, these organs are of great value to a predator that hunts at night, as well as for avoiding the snake’s own predators.^[8]

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.^[5]

Evolution

The earliest known fossil pit viper remains are from theEarly MioceneofNebraska.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.^[9]

Geographic range

The subfamily Crotalinae is found fromCentral Asiaeastward and southward toJapan,China,Indonesia,peninsularIndia,Nepal,andSri Lanka.In the Americas, they range from southernCanadasouthward to Central America to southern South America.^[1]

Habitat

Crotalines are a versatile subfamily, with members found inhabitatsranging from parcheddesert(e.g., the sidewinder,Crotalus cerastes) torainforests(e.g., the bushmaster,Lachesis muta). They may be eitherarborealorterrestrial,and at least one species (the cottonmouth,Agkistrodon piscivorus) is semiaquatic. The altitude record is held jointly byCrotalus triseriatusin Mexico andGloydius strauchiin China, both of which have been found above the treeline at over 4,000 m above sea level.^[5]

Behavior

Although a few species of crotalines are highly active by day, such asTrimeresurus trigonocephalus,a bright green pit viperendemicto 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.^[10]

As ambush predators, crotalines typically wait patiently somewhere for unsuspecting prey to wander by. At least one species, the arborealGloydius shedaoensisof 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.^[11]

Many temperate species of pit vipers (e.g. most rattlesnakes) congregate in sheltered areas or "dens" to overwinter (brumate, seehibernation), 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]}

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]}

Reproduction

With few exceptions, crotalines areovoviviparous,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 theoviparous(egg-laying) pit vipers areLachesis,Calloselasma,and someTrimeresurusspecies. All egg-laying crotalines are believed to guard their eggs.^{[citation needed]}

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.^[12]

Taxonomy

In the past, the pit vipers were usually classed as a separatefamily:the Crotalidae. Today, however, themonophylyof theviperinesand the crotalines as a whole is undisputed, which is why they are treated here as a subfamily of theViperidae.^{[citation needed]}

Genera

Genus^{[ref 1]}	Taxon author^{[ref 1]}	Species^{[ref 1]}	Common name	Geographic range^{[ref 2]}
Agkistrodon	Palisot de Beauvois,1799	6	Moccasins	North America from the northeastern and central USA southward through peninsularFloridaand southwesternTexas.In Central America on the Atlantic versant fromTamaulipasandNuevo Leónsouthward to theYucatán Peninsula,BelizeandGuatemala.Along the Pacific coastal plain and lower foothills fromSonorasouth through Guatemala,El Salvador,HondurasandNicaraguato northwesternCosta Rica.
Atropoides	Werman, 1992	1	Picado's jumping pit viper	Costa Rica and western Panama
Bothriechis	Peters,1859	11	Palm-pit vipers	Southern Mexico (southeasternOaxacaand the northern highlands ofChiapas), through Central America to northern South America (Colombia,westernVenezuela,Ecuadorand northernPeru
Bothrocophias	Gutberlet&Campbell,2001	9	Toadheaded pit vipers	Northern South America
Bothrops	Wagler,1824	48	Lanceheads	Northeastern Mexico (Tamaulipas) southward through Central and South America toArgentina;Saint LuciaandMartiniquein theLesser Antilles;Ilha da Queimada Grandeoff the coast of Brazil
Calloselasma	Cope,1860	1	Malayan pit viper	Southeast Asia fromThailandto northernMalaysiaandJava,Indonesia
Cerrophidion	Campbell & Lamar, 1992	5	Montane pit vipers	Southern Mexico (highlands ofGuerreroand southeastern Oaxaca), southward through the highlands of Central America (Guatemala, El Salvador, Honduras, northern Nicaragua, Costa Rica) to western Panama
Craspedocephalus	Kuhl&van Hasselt,1822	15	Pit viper	India toThailandto northernMalaysiaandIndonesia
Crotalus^T	Linnaeus,1758	51	Rattlesnakes	The Americas, from southern Canada to northern Argentina
Deinagkistrodon	Gloyd,1979	1	Hundred-pace pit viper	Southeast Asia
Garthius	Malhotra & Thorpe, 2004	1	Mount Kinabalu pit viper, Chasen's mountain pit viper	Borneo
Gloydius	Hoge & Romano-Hoge, 1981	22	Asian moccasins	Russia, east of theUral MountainsthroughSiberia,Iran,theHimalayasfrom Pakistan, India,Nepaland China, Korea, Japan and theRyukyu Islands
Hypnale	Fitzinger,1843	3	Hump-nosed pit vipers	Sri Lankaand India
Lachesis	Daudin,1803	4	Bushmasters	Central and South America
Metlapilcoatlus	Campbell, Frost, & Castoe, 2019	6	Jumping pit vipers	The mountains of eastern Mexico southeastward on the Atlantic versant and lowlands though Central America to centralPanama.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	3	Mexican pit vipers	Mexico
Ophryacus	Cope,1887	3	Mexican horned pit vipers	Mexico
Ovophis	Burger, 1981	7	Mountain pit vipers	Nepal andSeven Sisters(Assam) of India eastward throughMyanmar,Cambodia,Thailand,Laos,Vietnam,West Malaysia,Taiwan,Japan (Okinawa) and Indonesia (Sumatra)
Porthidium	Cope,1871	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	14	Pit vipers	Asia
Sistrurus	Garman,1883	3	Ground rattlesnakes	Southeastern Canada, eastern, central and northwestern USA, isolated populations in northern and central Mexico
Trimeresurus	Lacépède,1804	43	Asian lanceheads	Southeast Asia from India to southern China and Japan, and theMalay ArchipelagotoTimor
Tropidolaemus	Wagler,1830	5	Temple vipers	Southern India and Southeast Asia

*) Not including the nominate subspecies.^{[citation needed]}
^T)Type genus.^{[ref 2]}

^^a ^b ^c"Crotalinae".Integrated Taxonomic Information System.Retrieved26 October2006.
^^a ^bMcDiarmid 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).

References

^^a ^bMcDiarmid 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).
^^a ^b ^cMehrtens JM (1987).Living Snakes of the World in Color.New York: Sterling Publishers. 480 pp.ISBN 0-8069-6460-X.
^Sometimes spelled "pitvipers" – Campbell & Lamar, 2004^{[page needed]}
^"Crotalinae".Integrated Taxonomic Information System.Retrieved26 October2006.
^^a ^b ^c ^dCampbell 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.
^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).
^Bullock, T. H. and Diecke, F. P. J. (1956). Properties of an infrared receptor. Journal of Physiology 134, 47-87.
^Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp.ISBN 0-448-11856-4.
^"The first European pit viper from the Miocene of Ukraine - Acta Palaeontologica Polonica".app.pan.pl.Retrieved21 February2024.
^Krochmal, Aaron R.; Bakken, George S. (1 August 2003)."Thermoregulation is the pits: use of thermal radiation for retreat site selection by rattlesnakes".Journal of Experimental Biology.206(15): 2539–2545.doi:10.1242/jeb.00471.PMID 12819261.S2CID 18140029.Retrieved11 June2022.
^Shine R,Sun L, Kearney M, Fitzgerald M (2002). "Why do Juvenile Chinese Pit-Vipers (Gloydius shedoaensis) Select Arboreal Ambush Sites? "Ethology108:897–910. ISSN 0179-1613.PDF Archived24 July 2008 at theWayback Machineat University of SydneySchool of Biological Sciences.Accessed 26 October 2006.
^Heatwole, H.; Davison, Elizabeth (1976)."A Review of Caudal Luring in Snakes with Notes on Its Occurrence in the Saharan Sand Viper, Cerastes vipera".Herpetologica.32(3): 332–336.JSTOR 3891463.Retrieved24 August2021.

External links

Pit organs at Life is Short, but Snakes are Long

[ITIS-13] "Crotalinae".Integrated Taxonomic Information System.Retrieved26 October2006.

[McD99-14] 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).

[McD99-1] 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).

[Meh87-2] Mehrtens JM (1987).Living Snakes of the World in Color.New York: Sterling Publishers. 480 pp.ISBN 0-8069-6460-X.

[3] Sometimes spelled "pitvipers" – Campbell & Lamar, 2004^{[page needed]}

[ITIS-4] "Crotalinae".Integrated Taxonomic Information System.Retrieved26 October2006.

[C&L04-5] 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.

[P&G77-6] 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).

[B&H05-7] Bullock, T. H. and Diecke, F. P. J. (1956). Properties of an infrared receptor. Journal of Physiology 134, 47-87.

[Sti74-8] Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp.ISBN 0-448-11856-4.

[9] "The first European pit viper from the Miocene of Ukraine - Acta Palaeontologica Polonica".app.pan.pl.Retrieved21 February2024.

[K&B03-10] Krochmal, Aaron R.; Bakken, George S. (1 August 2003)."Thermoregulation is the pits: use of thermal radiation for retreat site selection by rattlesnakes".Journal of Experimental Biology.206(15): 2539–2545.doi:10.1242/jeb.00471.PMID 12819261.S2CID 18140029.Retrieved11 June2022.

[SHI-11] Shine R,Sun L, Kearney M, Fitzgerald M (2002). "Why do Juvenile Chinese Pit-Vipers (Gloydius shedoaensis) Select Arboreal Ambush Sites? "Ethology108:897–910. ISSN 0179-1613.PDF Archived24 July 2008 at theWayback Machineat University of SydneySchool of Biological Sciences.Accessed 26 October 2006.

[12] Heatwole, H.; Davison, Elizabeth (1976)."A Review of Caudal Luring in Snakes with Notes on Its Occurrence in the Saharan Sand Viper, Cerastes vipera".Herpetologica.32(3): 332–336.JSTOR 3891463.Retrieved24 August2021.

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