''Agkistrodon'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

pit viper The Crotalinae, commonly known as pit vipers,Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. . or pit adders, are a subfamily (biology), subfamily of Viperidae, vipers found in Asia and the ...

s commonly known as American moccasins.Crother, B. I. (ed.). 2017. ''Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, with Comments Regarding Confidence in Our Understanding.'' SSAR Herpetological Circular 43, 1–102 pp. (page 59)Liner, E. A. and G. Casas-Andreu. 2008. ''Standard Spanish, English and scientific names of the amphibians and reptiles of Mexico.'' Society for the Study Amphibians and Reptiles. Herpetological Circular 38: i-iv, 1-162. (pages 95-96) The genus is

endemic Endemism is the state of a species being found only 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 foun ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, ranging from the

Southern United States The Southern United States (sometimes Dixie, also referred to as the Southern States, the American South, the Southland, Dixieland, or simply the South) is List of regions of the United States, census regions defined by the United States Cens ...

to northern

Costa Rica Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...

. Eight species are currently recognized,Porras, Louis W., Larry David Wilson, Gordon W. Schuett, and Randall S. Reiserer 2013. ''A taxonomic reevaluation and conservation assessment of the common cantil, Agkistrodon bilineatus (Squamata: Viperidae): a race against time''. Amphibian & Reptile Conservation 7(1): 48–73. all of them

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

and closely related.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. . Common names include: cottonmouths, copperheads, and cantils.Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. .

Name origin

The name ''Agkistrodon'' comes from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

words (, 'fishhook', with the irregular transliteration ''gk'' rather than the usual ''nk'') and () 'tooth' and is likely a reference to the fangs. Some varieties of the genus are given the common name "moccasin" or "moccasin snake" in the United States, which is the Algonquian word for "

shoe A shoe is an item of footwear intended to protect and comfort the human foot. Though the human foot can adapt to varied terrains and climate conditions, it is vulnerable, and shoes provide protection. Form was originally tied to function, but ...

". The origin of this nickname is unknown. The first known use of "moccasin" to refer to a deadly venomous snake was in a 1765 publication. The nickname is used to refer to both cottonmouths and copperheads. According to the Word Detective, this use may be related to their color and appearance or the silence with which they move. Another source for this name may be the Native American word "mokesoji" of unknown origin and meaning.

Description

Members of this genus have a number of features in common. All species have a relatively broad head with short fangs. A

loreal scale The lore (adj. loreal) is the region between the eyes and nostrils of birds, reptiles, and amphibians. Ornithology In ornithology, the lore is the region between the eye and bill on the side of a bird's head. This region is sometimes featherless ...

is present, except in '' A. piscivorus''. Usually, nine large symmetrical platelike scales are on the crown of the head, but in all species, these are often irregularly fragmented or have sutures, especially in '' A. bilineatus''. All have a sharply defined canthus rostralis and a vertically elliptical pupil. Usually eight (6-10)

supralabial scales In reptiles, the supralabial scales, also called upper-labials, are those scales that border the mouth opening along the upper jaw. They do not include the median scaleWright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates ( ...

and usually 10-11 (8-13) sublabials are present. The

dorsal scales In snakes, the dorsal scales are the longitudinal series of plates that encircle the body, but do not include the ventral scales. Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publis ...

are mostly keeled and at midbody number 21-25 (usually 23), while ''A. piscivorus'' has 23-27 (usually 25). The snake has 127-157

ventral scales In snakes, the ventral scales or gastrosteges are the enlarged and transversely elongated scales that extend down the underside of the body from the neck to the anal scale. When counting them, the first is the anteriormost ventral scale that cont ...

and 36-71

subcaudals In snakes, the subcaudal scales are the enlarged plates on the underside of the tail. Wright AH, Wright AA (1957). ''Handbook of Snakes of the United States and Canada''. Comstock Publishing Associates, a Division of Cornell University Press. (7t ...

. Of the latter, some may be divided. The anal scale is single. All have a color pattern of 10-20 dark crossbands on a lighter ground color, although sometimes the crossbands are staggered as half bands on either side of the body. The

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

of the species has long been controversial. Studies based on morphological and venom characteristics support the idea that ''A. bilineatus'' and ''A. contortrix'' are more closely related. However, an analysis of

mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the D ...

, as well as more recent molecular studies,Parkinson CL, Moody SM, Ahlquist JE (1997). "Phylogenetic relationships of the "''Agkistrodon'' complex" based on mitochondrial DNS data". pp. 63-78. ''In'': Thorpe RS, Wüster W, Malhotra A (1997). ''Venomous Snakes: Ecology, Evolution, and Snakebite''. Oxford: Clarendon Press have concluded that ''A. bilineatus'' and ''A. piscivorus'' are sister taxa, with ''A. contortrix'' being a sister species to them both.

Geographic range

They are found in

from the northeastern and central United States southward through peninsular

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

and southwestern

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

, and in

Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...

on the Atlantic versant from

Tamaulipas Tamaulipas, officially the Free and Sovereign State of Tamaulipas, is a state in Mexico; one of the 31 states which, along with Mexico City, comprise the 32 federal entities of Mexico. It is divided into 43 municipalities. It is located in nor ...

and

Nuevo León Nuevo León, officially the Free and Sovereign State of Nuevo León, is a Administrative divisions of Mexico, state in northeastern Mexico. The state borders the Mexican states of Tamaulipas, Coahuila, Zacatecas, and San Luis Potosí, San Luis ...

southward to the Yucatan Peninsula,

Belize Belize is a country on the north-eastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a maritime boundary with Honduras to the southeast. P ...

, and

Guatemala Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...

. They are seen along the Pacific coastal plain and lower foothills from

Sonora Sonora (), officially Estado Libre y Soberano de Sonora (), is one of the 31 states which, along with Mexico City, comprise the Administrative divisions of Mexico, Federal Entities of Mexico. The state is divided into Municipalities of Sonora, 72 ...

south through Guatemala,

El Salvador El Salvador, officially the Republic of El Salvador, is a country in Central America. It is bordered on the northeast by Honduras, on the northwest by Guatemala, and on the south by the Pacific Ocean. El Salvador's capital and largest city is S ...

Honduras Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...

, and

Nicaragua Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...

to northwestern

Behavior

All are semiaquatic to terrestrial and are often found near sources of water. However, ''A. contortrix'' and ''A. bilineatus'' are also found in dry habitats, often far from permanent streams or ponds.

Reproduction

The members of this genus are all

ovoviviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a "bridging" form of reproduction between egg-laying oviparity, oviparous and live-bearing viviparity, viviparous reproduction. Ovoviviparous animals possess embryos that develo ...

. A 2012 study found that they are not only capable of parthenogenesis (asexual reproduction), but that litters created without a male may account for up to 5% of litters in the wild, even in areas that have males present. This phenomenon had previously only been observed in captive populations

Venom

Pit vipers of the genus ''Agkistrodon'' rely on a potent

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

they produce for their survival. Used to immobilize

prey Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not ki ...

and fend off

predators Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

, one bite can inject enough venom into a human to cause severe pain, swelling, weakness, difficulty breathing, hemorrhaging, gangrene, fever, vomiting, and in rare instances, even death."Agkistrodon acutus pit vipers." Medical-Explorer.com; accessed April 2010

/ref> The venom of all three species is assumed to be not unlike that of ''A. contortrix'', which contains thrombin-like enzymes that act upon the coagulant activity of the blood. A study of Electrophoresis, electrophoretic patterns of proteins in venoms among and within populations of ''A. contortrix'' and ''A. piscivorus'' showed that substantial variation exists, and no reason exists to believe that these differences do not correspond with variations in toxicity.

Research

In a study conducted at the College of Medicine at the

University of Florida The University of Florida (Florida or UF) is a public university, public land-grant university, land-grant research university in Gainesville, Florida, United States. It is a senior member of the State University System of Florida and a preem ...

, venom from ''A. piscivorous'' was injected into the

lymph fluid Lymph () is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to be recirculated. At the origi ...

of a

frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...

. The frog immediately suffocated because of the collapse of its lung sacs. The venom even resulted in lung constriction when directly applied to the surface of the frog's lungs. To test this, trace amounts of venom were dropped onto a single pulmonary sac in a frog's lung after it was anesthetized and its chest cavity dissected open. A drop of solution containing a venom concentration of 1 mg/ml was enough to cause contraction of the

pulmonary artery A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and ...

adventitia after 5-8 sec in a frog weighing 40 g. The study found, however, that this toxic effect is simply a tool the snake can choose to employ from an accessory venom gland it has. In most instances, the viper injects a venom that tends to immobilize, not kill, its prey before

ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms, inge ...

. In this case, the main venom glands secrete a toxin that inhibits the prey's sympathetic response to flee or fend off its predator. This essentially stuns the animal so that the predator can easily attack.

Species

Type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

Taxonomy

This genus was previously much larger and also included the following genera: * '' Calloselasma'' - Ground pit viper found in

Southeast Asia Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...

(Malaya). * '' Deinagkistrodon'' - The Hundred-pace viper found mostly in southern China. * ''

Gloydius ''Gloydius'' is a genus of pit vipers endemic to Asia, also known as Asian moccasins or Asian ground pit vipers. Named after American herpetologist Howard K. Gloyd, Beolens, Bo; Watkins, Michael; Grayson, Michael (2011). ''The Eponym Dictionar ...

'' - Ground pit vipers found in

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

. * '' Hypnale'' - Hump-nosed vipers found in India and

Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...

References

External links

* {{Authority control Snake genera Taxa named by Palisot de Beauvois