Crotalus

Crotalus is a genus of pit vipers, commonly known as rattlesnakes or rattlers,<ref name="W&W57">Wright AH, Wright AA (1957). Handbook of Snakes of the United States and Canada. Ithaca and London: Comstock Publishing Associates (7th printing, 1985). 1,105 pp. (in 2 volumes). Template:ISBN.</ref> in the family Viperidae. The genus is found only in the Americas from southern Canada to northern Argentina.<ref name="McD99"/> The generic name Crotalus is derived from the Greek word {{#invoke:Lang|lang}} krótalοn, which means "rattle" or "castanet", and refers to the rattle on the end of the tail, which makes this group (genera Crotalus and Sistrurus) so distinctive.<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. Template:ISBN.</ref> As of July 2023, 44<ref name="ITIS">{{#if:174305 | {{#invoke:template wrapper|wrap|_template=cite web|_exclude=id,ID,taxon

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 | title = Crotalus 
 | publisher = Integrated Taxonomic Information System
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| Template:Citation error }}</ref> to 53<ref>Template:EMBL genus www.reptile-database.org.</ref> species are recognized as valid.

Description

Members of the genus Crotalus range in size from only Template:Convert (C. intermedius, C. pricei), to over Template:Convert (eastern and western diamondback rattlesnakes).<ref name="C&L04"/> In general, adult males are slightly larger than females. Compared to most snakes, they are heavy-bodied, although some African vipers are much thicker.<ref name="Kla97">Klauber LM (1997). Rattlesnakes: Their Habitats, Life Histories, and Influence on Mankind. Second Edition. (First published in 1956, 1972). Berkeley: University of California Press. Template:ISBN.</ref> Most forms are easily recognized by the characteristic rattle on the end of their tails, although a few island populations form exceptions to this rule: C. catalinensis has lost its rattle entirely, Crotalus lorenzoensis usually has no rattle, and both Crotalus ruber lucasensis and Crotalus estebanensis exhibit a tendency for rattle loss. The rattle may also be lacking in any species due to a congenital abnormality.<ref name="C&L04"/>

File:Rattle.jpg

The rattle of a western diamondback rattlesnake (note the black and white colour at the base)

The rattle consists of a series of loosely interlocking hollow shells, each of which was at one point the scale covering the tip of the tail. In most other snakes, the tail tip, or terminal spine, is cone-shaped, hardly any thicker than the rest of the skin, and is shed along with it at each successive molt. In this case, the end scale, or "button", is much thicker and shaped like a bulb, with one or two annular constrictions to prevent it from falling off. Before each molt, a new button will have developed inside the last one and before the skin is shed off its body, the tip of the new button shrinks, then loosening the shell of the previous one. This process continues so the succession of molts produces an appendage consisting of a number of interlocking segments that make an audible noise when vibrated. Since younger specimens may shed several times in a year at a frequency that depends on their environment and how much they eat, every time adding a new segment to the rattle, the number of segments is a function of more than solely the age of the snake. In theory, the rattle could become very long indeed, but in practice, the older segments tend to wear out and fall off. How quickly this happens depends on the snake's environment, but end segments tend to break off after the rattle becomes about six or seven segments long; nonetheless, finding specimens with as many as a dozen segments is not uncommonTemplate:Px2Template:Mdash⁠Template:Hspand in captive specimens, as many as 29 segments have been documented.<ref name="P&G77">Parker HW, Grandison AGC (1977). Snakes — a natural history. Second Edition. London and Ithaca: British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. Template:ISBN (cloth), Template:ISBN (paper).</ref><ref name="Sti74">Stidworthy J (1974). Snakes of the World. New York: Grosset & Dunlap Inc. 160 pp. Template:ISBN.</ref>

Distribution and habitat

The genus Crotalus is found in the Americas from southern Canada to central Argentina.<ref name="McD99"/><ref>Template:Cite journal</ref><ref name="DuarteMenezes2013">Template:Cite journal</ref>

Behavior

No species of Crotalus is considered aggressive; when threatened, most retreat quickly, but most species defend themselves readily when cornered.<ref name="C&L04"/>

There is no consensus in the available literature about how far rattlesnakes can strike, with estimates ranging from one-third to the entire body length of the rattlesnake. Strike distance depends not just on the snake’s size, but also on many other factors, including its species, the position of its body, and its degree of agitation. This is compounded by a further lack of consensus as to the location on the anchor coil of the snake from where a strike should be measured. They rarely strike further than half of their body length, and almost never more than three-fourths, but trusting such values is unwise if only because it is not feasible to accurately judge the length of a coiled snake.<ref name="Kla97" />

Feeding

The diets of species of Crotalus generally consist of vertebrates, although many invertebrate species are also consumed. Smaller species feed mainly on lizards, while larger species start by feeding on lizards as juveniles and then switch to preying mainly on mammals as adults. Prey items more frequently taken include rabbits, ground squirrels such as prairie dogs, tree squirrels, chipmunks, gophers, and rats and mice,<ref>Klauber, 1936, 1971, 1972.</ref> while those less frequently taken include birds, snakes, and amphibians. Cannibalism has been reported in a number of different species. Individuals that feed on rodents usually release their prey after a strike to avoid their teeth, and these snakes evidently can discriminate between trails left by prey that has or has not been envenomated.<ref name="C&L04"/>Template:Rp

Predators

For all species of Crotalus, the most significant threats come from people, but they also face many natural enemies. These include other snakes, such as kingsnakes (Lampropeltis), coachwhips (Masticophis), indigo snakes (Drymarchon), and racers (Coluber); birds, such as hawks, eagles, owls, roadrunners, and ravens; and mammals, such as cats, coyotes, foxes, wildcats, badgers, skunks, and pigs.<ref>Keegan, 1944; Klauber, 1927, 1936, 1971, 1972.</ref> Certain species of birds frequently prey on these snakes, but this is not without risk. Two cases were reported in which dead hawks found near venomous snakes had suffered hemorrhage and gangrenous necrosis due to snakebite.<ref name="C&L04"/>Template:Rp

Reproduction

The genus Crotalus is ovoviviparous, giving birth to live young.<ref name="Kla97"/> The basic lifecycle of many Nearctic species has been known for quite some time. Females at an age of 26 months undergo vitellogenesis as they enter their third hibernation,<ref>Klauber, 1936.</ref> mate the following spring, and give birth later in September or October.<ref name="C&L04"/>Template:Rp

Several variations to this basic cycle occur. In North America, the females of some species store sperm in their oviducts for at least eight months, and the males (all species of which undergo spermatogenesis during the summer) store sperm in the vas deferens for at least a year. Thus, species that store sperm for a shorter duration mate in the spring and store sperm in the vas deferens, while those that do so for a longer duration mate in the fall and store sperm in the oviduct over the winter, after which fertilization occurs the following spring.<ref name="C&L04"/>Template:Rp In addition, species that occur further north, where weather is colder during much of the year and the feeding and growing season is short, may reproduce only every other year or less. Those found in central and southern Mexico or the tropics have reproductive cycles that correspond mostly with the rainy season.<ref name="C&L04"/>Template:Rp

Venom

Two main hemotoxic effects are caused by rattlesnake venom. First, zinc-containing metalloproteases act upon capillary endothelial cells to inhibit platelet aggregation and hemorrhage.<ref name="CHI">Template:Cite journal</ref> Second, the platelet antagonist crotalin creates a severe bleeding effect as it binds to the surface proteins, blocking aggregation.<ref name="HATI">Template:Cite journal</ref>

Neurotoxic effects may also be caused by rattlesnake venom. These effects vary by species, and within species by population.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Species

Image	Species<ref name="ITIS"/>	Taxon author<ref name="ITIS"/>	Subsp.*<ref name="ITIS"/>	Common name<ref name="C&L04"/>	Geographic range<ref name="McD99"/>
File:Crotalus adamanteus 25.jpg	C. adamanteus	Palisot de Beauvois, 1799	0	Eastern diamondback rattlesnake	The southeastern United States from southeastern North Carolina, south along the coastal plain through peninsular Florida to the Florida Keys, and west along the Gulf Coast through southern Mississippi to southeastern Louisiana
	C. angelensis	Klauber, 1963	0	Angel de la Guarda Island speckled rattlesnake	Isla Ángel de la Guarda in the Gulf of California, Mexico
File:Crotalus aquilus.jpg	C. aquilus	Klauber, 1952	0	Querétaro dusky rattlesnake	The highlands of central Mexico: Guanajuato, Hidalgo State of Mexico, Michoacán, and San Luis Potosí
File:Crotalus armstrongi in Morelia zoo.jpg	C. armstrongi	Campbell, 1979	0	Western dusky rattlesnake	Mexico: Jalisco and Nayarit
File:Crotalus atrox USFWS.jpg	C. atrox	Baird & Girard, 1853	0	Western diamondback rattlesnake	The Southwestern United States from central Arkansas and southeastern California, south into Mexico as far as northern Sinaloa, Hidalgo, and northern Veracruz, disjunct populations in southern Veracruz and southeastern Oaxaca
File:Crotalus basiliscus.jpg	C. basiliscus	(Cope, 1864)	0	Mexican west coast rattlesnake	Western Mexico from southern Sonora to Michoacán
	C. campbelli	Bryson, Linkem, Dorcas, Lathrop, Jones, Alvarado-Diaz, Grünwald & Murphy, 2014	0	Campbell's rattlesnake	Mexico: western Jalisco, northwestern Colima
File:Gfp-santa-cataline-island-rattlesnake.jpg	C. catalinensis	Cliff, 1954	0	Santa Catalina rattlesnake	Isla Santa Catalina in the Gulf of California (western Mexico)
File:Crotalus cerastes mesquite springs CA-2.jpg	C. cerastes	Hallowell, 1854	2	Sidewinder, Horned rattlesnake	The southwestern United States in the desert region of eastern California, southern Nevada, extreme southwestern Utah, and western Arizona, northwestern Mexico in western Sonora and eastern Baja California
File:Arizona Black Rattlesnake.jpg	C. cerberus	(Coues, 1875)	0	Arizona black rattlesnake	Central Arizona to western New Mexico
File:Crotalus oreganus concolor 01.jpg	C. concolor	(Woodbury, 1929)	0	Midget faded rattlesnake	basins of the Colorado and Green Rivers in the United States
File:Gfp-northwestern-neotropical-rattlesnake.jpg	C. culminatus	Klauber, 1952	0	Northwestern neotropical rattlesnake	Mexico in southwestern Michoacán, southern and western Morelos, Guerrero, and southwestern Oaxaca, probably in extreme western Puebla and possibly in the Mexican Federal District
File:Cascabelle.JPG	C. durissus	Linnaeus, 1758	6	South American rattlesnake	All South American countries except Chile and Ecuador (although the various populations are disjunct), some islands in the Caribbean<ref name="C&L04"/>
	C. ehecatl	Carbajal-Marquez, Cedeno-Vazquez, Martinez-Arce, Neri-Castro, & Machkour-M’rabet, 2020	0	Tehuantepec Isthmus Neotropical rattlesnake	Mexico: (Chiapas, Oaxaca)
File:Crotalus enyo.JPG	C. enyo	(Cope, 1861)	2	Baja California rattlesnake	Western Mexico on the Baja California Peninsula from around Río San Telmo on the west coast and from opposite Isla Ángel de la Guarda on the Gulf Coast, south to Cabo San Lucas, on the following islands in the Gulf of California: San Marcos, Carmen, San José, San Francisco, Partida del Sur, Espírita Santo, and Cerralvo, off the Pacific coast on Isla Santa Margarita
	C. ericsmithi	Campbell & Flores-Villela, 2008	0	Guerreran long-tailed rattlesnake	Western Mexico: Guerrero
	C. estebanensis	Klauber, 1949	0	San Esteban Island rattlesnake	Mexico: Isla San Esteban (Gulf of California)
File:Crotalus viridis helleri.jpg	C. helleri	(Meek, 1905)	0	Southern Pacific rattlesnake	SW California, Baja California, Mexico
File:ZollmanTimberRattlesnake.jpg	C. horridusT	Linnaeus, 1758	0	Timber rattlesnake	The eastern United States from southern Minnesota and southern Maine, south to east Texas and north Florida, in southern Canada in southern Ontario
File:Mexican Smallhead Rattlesnake imported from iNaturalist photo 46759429 on 5 February 2022.png	C. intermedius	Troschel, 1865	2	Mexican small-headed rattlesnake	Central and southern Mexico, in southeastern Hidalgo, southern Tlaxcala, northeastern and south-central Puebla, west-central Veracruz, Oaxaca and Guerrero
	C. lannomi	W. Tanner, 1966	0	Autlán rattlesnake	Western Mexico in Jalisco
File:Crotalus lepidus lepidus 1.jpg	C. lepidus	(Kennicott, 1861)	2	Rock rattlesnake	The southwestern United States in Arizona, southern New Mexico, and southwestern Texas, south into north-central Mexico
	C. lorenzoensis	Radcliffe & Maslin, 1975	0	San Lorenzo Island red diamond rattlesnake	Mexico, San Lorenzo Island in the Gulf of California
File:Rattlesnake (Marshal Hedin).jpg	C. lutosus	(Klauber, 1930)	0	Great Basin rattlesnake	Great Basin between the Rocky Mountains and the Sierra Nevada
	C. mictlantecuhtli	Carbajal-Marquez, Cedeno-Vazquez, Martinez-Arce, Neri-Castro, & Machkour-M’rabet, 2020	0	Veracruz Neotropical rattlesnake	Mexico: (Veracruz)
File:Speckled Rattlesnake (Crotalus mitchellii) (21705787199).jpg	C. mitchellii	(Cope, 1861)	1	Speckled rattlesnake	Mexico: most of Baja California Sur and on a number of islands in the Gulf of California and on Isla Santa Margarita off the Pacific coast of Baja California Sur
File:Northern black-tailed rattlesnake.jpg	C. molossus	Baird & Girard, 1853	2	Black-tailed rattlesnake	The southwestern United States (Arizona, south-western New Mexico), and Mexico from Sonora and western Chihuahua as far south as Oaxaca, in the Gulf of California on San Esteban Island and Tiburón Island
File:Crotalus morulus, Tamaulipan Rock Rattlesnake, Tamailipas.jpg	C. morulus	Klauber, 1952	0	Tamaulipan rock rattlesnake	Mexico (Sierra Madre Oriental: Tamaulipas, Nuevo León, Coahuila)
File:Crotalus oreganus.jpg	C. oreganus	Holbrook, 1840	0	Western rattlesnake	Southwestern Canada (southern British Columbia), south through the northwestern half of the United States (Washington, Oregon, western and southern Idaho, California<ref name="C&L04"/>
File:Crotalus ornatus 158434960.jpg	C. ornatus	Hallowell, 1854	0	Eastern black-tailed rattlesnake	The southwestern United States (New Mexico, western and central Texas) and north-eastern Mexico (Chihuahua, Coahuila)
	C. polisi	Meik, Schaack, FloreS-Villela, & Streicher, 2018	0	Horsehead Island speckled rattlesnake	Cabeza de Caballo Island, Baja California, Mexico
File:Crotalus Polystictus.jpg	C. polystictus	(Cope, 1865)	0	Mexican lance-headed rattlesnake	Central Mexican Plateau, from southern Zacatecas and northeastern Colima east to east-central Veracruz
File:Crotalus pricei.jpg	C. pricei	Van Denburgh, 1895	1	Twin-spotted rattlesnake	In the US from southeastern Arizona, and Mexico in northern Sonora southeast through Chihuahua, Durango, southeastern Coahuila, and Nuevo León into Tamaulipas
File:Crotalus pusillus 72647737.jpg	C. pusillus	Klauber, 1952	0	Tancitaran dusky rattlesnake	West-central Mexico in southwestern and west-central Michoacán and adjacent Jalisco, probably also in northeastern Colima
File:Crotalus-mitchellii.jpg	C. pyrrhus	Cope, 1867	0	Southwestern speckled rattlesnake	Southwestern United States (western Arizona, southern California, southern Nevada, extreme south-western Utah) and northwestern Mexico (Baja California del Norte, northwestern Sonora)
File:Crotalus ravus cropped2.jpg	C. ravus	(Cope, 1865)	2	Mexican pygmy rattlesnake	The mountains of central and southern Mexico, west of the Isthmus of Tehuantepec, in the southeastern part of the Mexican Plateau, in the highlands of Morelos, Tlaxcala, Puebla, Veracruz, Oaxaca, and the Sierra Madre del Sur in Guerrero
File:Crotalus ruber 02.jpg	C. ruber	Cope, 1892	2	Red diamond rattlesnake	The US in southwestern California, south through the Baja California Peninsula, except in the desert east of the Sierra de Juárez, also on a number of islands in the Gulf of California and three islands off the west coast of Baja California Sur
File:Crotalus scutulatus 02.JPG	C. scutulatus	(Kennicott, 1861)	1	Mojave rattlesnake	The southwestern US in southern California, southern Nevada, extreme southwestern Utah, most of Arizona, southern New Mexico, and West Texas, and south into Mexico to southern Puebla
File:Yucatan Neotropical Rattlesnake 045.jpg	C. simus	Latreille In Sonnini & Latreille, 1801	0	Middle American rattlesnake	From Mexico in southwestern Michoacán on the Pacific coast, and Veracruz and the Yucatán Peninsula on the Atlantic coast, south through Belize, Guatemala, El Salvador, Honduras, and Nicaragua to west-central Costa Rica<ref name="C&L04"/>
	C. stejnegeri	Dunn, 1919	0	Long-tailed rattlesnake	Western Mexico in eastern Sinaloa, western Durango, and probably northern Nayarit
File:Crotalus stephensi.JPG	C. stephensi	Klauber, 1930	0	Panamint rattlesnake	United States: eastern California, southwestern Nevada
	C. tancitarensis	Alvarado-Diaz & Campbell, 2004	0	Tancitaro rattlesnake	Mexico: Michoacán
	C. thalassoporus	Meik, Schaack, FloreS-Villela, & Streicher, 2018	0	Louse Island speckled rattlesnake	Piojo Island, Baja California, Mexico
File:Tiger Rattlesnake 001.jpg	C. tigris	Kennicott in Baird, 1859	0	Tiger rattlesnake	The southwestern US in south-central Arizona, and in northwestern Mexico in Sonora, on Isla Tiburón in the Gulf of California
	C. tlaloci	Bryson, Linkem, Dorcas, Lathrop, Jones, Alvarado-Diaz, Grünwald & Murphy, 2014	0		Mexico: Michoacan and Guerrero
File:Crotalus totonacus, Totonacan Rattlesnake, Tamaulipas.jpg	C. totonacus	Gloyd & Kauffeld, 1940	0	Totonacan rattlesnake	Northeastern Mexico from central Nuevo León through southern Tamaulipas, northern Veracruz, eastern San Luis Potosí, and northern Querétaro.<ref name="C&L04"/>
File:Gfp-cross-banded-rattlesnake.jpg	C. transversus	Taylor, 1944	0	Cross-banded mountain rattlesnake	Central Mexico in the State of Mexico and Morelos.
File:Crotalus triseriatus in Morelia zoo.jpg	C. triseriatus	(Wagler, 1830)	1	Mexican dusky rattlesnake	Mexico, along the southern edge of the Mexican Plateau in the highlands of the Transverse Volcanic Cordillera, including the states of Nayarit, Jalisco, Michoacán, Morelos, México, Puebla, Tlaxcala, and Veracruz
File:Crotalus-simus-tzabcan.jpg	C. tzabcan	Klauber, 1952	0	Yucatán neotropical rattlesnake	Mexico (Yucatán, Campeche, Quintana Roo, and eastern Tabasco), northern Guatemala and northern Belize<ref>Acevedo M, Johnson J, Ariano-Sánchez D (2014). "Crotalus tzabcan ". The IUCN Red List of Threatened Species 2014: e.T197478A2488339. https://dx.doi.org/10.2305/IUCN.UK.2014-1.RLTS.T197478A2488339.en. Downloaded on 30 April 2021.</ref>
File:Crotalus unicolor.jpg	C. unicolor	Klauber, 1936	0	Aruba rattlesnake	Aruba
File:Crotale venezuela 19.JPG	C. vegrandis	Klauber, 1941	0	Uracoan rattlesnake	Eastern Venezuela
File:Crotalus viridis 02.jpg	C. viridis	(Rafinesque, 1818)	1	Prairie rattlesnake	Southern Canada (Alberta, Saskatchewan), south through the US (eastern Idaho, Montana, North Dakota, South Dakota, Wyoming, Nebraska, Colorado, Kansas, Oklahoma, Texas, New Mexico, extreme eastern Arizona), and into northern Mexico (northern Coahuila, northwestern Chihuahua)<ref name="C&L04"/>
File:Arizona ridgenosed rattlesnake closeup.jpg	C. willardi	Meek, 1905	4	Ridge-nosed rattlesnake	The US in southeastern Arizona and southwestern New Mexico, and northwestern Mexico in Sonora, Chihuahua, Durango, and Zacatecas

*) Not including the nominate subspecies
^T) Type species<ref name="McD99"/>

See also

• Snakebite

Further reading

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• Coues E (1875). "Synopsis of the Reptiles and Batrachians of Arizona; with Critical and Field Notes, and an Extensive Synonymy". pp. 585–633 [609]. In: Wheeler GM (1875). Report Upon Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian. Volume V. Zoology: Reports Upon the Zoological Collections Obtained from Portions of Nevada, Utah, California, Colorado, New Mexico, and Arizona, During the Years 1871, 1872, 1873, and 1874. Washington, District of Columbia: United States Government Printing Office.
• Fitzinger L (1843). Systema Reptilium. Fasciculus Primus. Amblyglossae. Vienna: Braumüller et Seidel. 106 pp. + indices [29]. (in Latin).
• Gloyd HK (1940). "The Rattlesnakes, Genera Sistrurus and Crotalus. A Study in Zoogeography and Evolution". Special Publ. Chicago Acad. Sci. (4): 1-266, 10 figures, 31 plates.
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• Houttuyn, M (1764). Natuurlyke historie of uitvoerige beschryving der dieren, planten en mineraalen, volgens het samenstel van den Heer Linnæus. Met naauwkeurige afbeeldingen. Eerste deels, zesde stuk. Dieren van beiderley leven. Amsterdam. 558 pp. [290]. (in Dutch).
• Hubbs B, O'Connor B (2012). A Guide to the Rattlesnakes and other Venomous Serpents of the United States. Tempe, Arizona: Tricolor Books. 129 pp. Template:ISBN.
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• Klauber LM (1971). "Classification, distribution and biology of the venomous snakes of northern Mexico, the United States and Canada: Crotalus and Sistrurus ". pp. 115–156. In: Bucherl, Wolfgang; Buckley, Eleanore E. (1971). Venomous Animals and Their Venoms, Volume II, Venomous Vertebrates. New York: Academic Press. 687 pp. Template:ISBN.
• Klauber LM (1972). Rattlesnakes: Their habits, Life Histories, and Influence on Mankind. Second edition. 2 Volumes. Berkeley, California: University of California Press.
• Laurenti JN (1768). Specimen medicum, exhibens synopsin reptilium emendatum cum experimentis circa venena et antidota reptilium austriacorum. Vienna: Joan. Thom. Nob. de Trattern. 214 pp. + Plates I-V [92]. (in Latin).
• Linnaeus C (1758). Systema naturae per regna tria naturae secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio Decima, Reformata [ Tenth Revised Edition, Volume 1]. Stockholm. 824 pp. [214]. (in Latin).
• Powell R, Conant R, Collins JT (2016). Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America, Fourth Edition. Boston and New York: Houghton Mifflin Harcourt. xiv + 494 pp. [438] + Plates 1-47. Template:ISBN.
• Rafinesque CS (1815). Analyse de la nature ou tableau de l'univers et des corps organisés. Palermo: Jean Barravecchia. 224 pp. (Herpetology section) pp. 73–78 [77]. (in French).
• Rafinesque CS (1820). "Annals of Nature, or Annual Synopsys of New Genera and Species of Animals and Plants Discovered in North America". Lexington (22): 1-16 [5].
• Reuss T (1930). "Glasnik Zemaljskog Muzeja u Bosni I Hercegovini ". Sveska za Prirodne Nauke 42: 57-114 [60, 88]. (in Bosnian).
• Schmidt KP, Davis DD (1941). Field Book of Snakes of the United States and Canada. New York: G.P. Putnam's Sons. 365 pp. [290-293].
• Wagler J (1830). Natürliches system der amphibien, mit vorangehender classification der Säugthiere und Vögel. Ein Beitrag zur vergleichenden Zoologie. Munich, Stuttgart and Tübingen: J.G. Cotta. vi + 354 pp. + one plate [176]. (in German and Latin).

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