''Hydrodynastes gigas'' is a New World

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of large, rear-fanged, Dipsadidae snake

endemic Endemism is the state of a species being found 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 found else ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

. It is commonly and alternatively known as the false water cobra and the Brazilian smooth snake.Warrell DA (2004). "Snakebites in Central and South America: Epidemiology, Clinical Features, and Clinical Management". ''In'': Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publishing Associates. 870 pp., 1,500 plates. . The false water cobra is so named because when the snake is threatened it "hoods" as a true cobra (''

Naja ''Naja'' is a genus of venomous elapid snakes commonly known as cobras (or "true cobras"). Members of the genus ''Naja'' are the most widespread and the most widely recognized as "true" cobras. Various species occur in regions throughout Afric ...

'' species) does. Unlike a true cobra, though, it does not rear up, but remains in a horizontal position. No subspecies are currently recognized as being valid.

Common names

''Hydrodynastes gigas'' is commonly referred to as the false water cobra, false cobra, South American water cobra, and Brazilian smooth snake. In South America, it is sometimes referred to as ''boipevassu''. Additional South American common names include ''mboi-peba, ñacaniná, surucucu-do-pantanal, vibora ladradora'' (barking snake), and ''yacanina''. Freiberg M (1982). ''Snakes of South America''. Hong Kong: T.F.H. Publications. 189 pp. . (''Hydrodynastes gigas'', pp. 78-79, 99, 132-133 + photographs on pp. 5, 50).

Description

''H. gigas'' is a large dipsadidae snake that may exceed 3 m (9 to 10 ft) in total length (including tail) when adult. Most ''H. gigas'' snakes reach about 2 m (6 to 7 ft) in total length. It is of medium body, so is neither particularly heavy nor slender-bodied, Weights can average around and exceed in mature adults, with some specimens weighing . Males are typically much smaller than females in this species. The common name false water cobra is an allusion to its ability to flatten its neck, similar to a cobra, as a defensive reaction to make it look larger and more intimidating. Unlike the true cobra, though, the false water cobra stays in a horizontal position when it hoods, rather than rearing into a vertical position. ''H. gigas'' can flatten not only its neck, but also lower down its body, which is not possible for a true cobra.

Additionally, the pattern and coloration of this ''Hydrodynastes'' species superficially resemble those of true water cobras (''

Boulengerina ''Boulengerina'' is a genus or subgenus of elapid venomous snakes known commonly as water cobras, so named because of their semiaquatic nature. The genus has two recognised species, which are native to central and southern Africa. Taxonomy Som ...

''). The false water cobra has large eyes with circular pupils, allowing good daytime vision. The tongue is black, and of the typical snake fashion. The background colour of a mature specimen is an olive green or brown, with dark spots and bands covering much of its body. The background coloring and banding generally become darker towards the tail. This colouring gives the false water cobra effective camouflage in its natural rainforest environment. The

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 ...

are yellow or brown, spotted with dark flecks that make three dotted lines, which appear to merge towards the tail. Mehrtens, 1987, suggested females are brown ventrally, whilst males are yellow. Females are suggested to have lighter bands and markings on their bodies. This is not an effective way of judging the sex of ''H. gigas'', as coloring differs slightly between all individuals. Hatchlings and juveniles are much darker in coloration and do not have the typical dark eyes of the adults. They more resemble a garter or water snake than their mature counterparts. In captivity, hypomelanstic animals have been produced. These animals vary in coloration, from some having only slightly lighter colored saddles, to those that are almost patternless. A melanistic population found in

Tocantins Tocantins () is one of the 26 states of Brazil. It is the newest state, formed in 1988 and encompassing what had formerly been the northern two-fifths of the state of Goiás. Tocantins covers and had an estimated population of 1,496,880 in 20 ...

, central Brazil, was originally describe as a new species of ''Hydrodynastes'', ''H. melanogigas,'' but genetic evidence indicates that this population is composed of melanistic ''H. gigas.''

Geographic range

In South America, ''H. gigas'' is found from eastern Bolivia to southern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, and in

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

and

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

Habitat

''H. gigas'' generally lives in wet, humid areas, and

marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...

lands, typically within the

tropical rainforest Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equa ...

s that are common within its range. However, the false water cobra has also been observed in dryer areas, although this is not its preferred habitat. The preference of wetlands as a habitat for ''H. gigas'' contributes to its common name of false "water" cobra.

Behavior

''H. gigas'' is primarily a diurnal species. It is also a very active and inquisitive snake, which spends much of the day climbing, burrowing, and even swimming. Temperaments can vary considerably between specimens; some are very docile and reluctant to bite, whilst others are very defensive and even aggressive or intimidating. Captive-bred specimens can become quite tame and trusting, and many exhibit a high level of intelligence.

Feeding

In the wild, ''H. gigas'' primarily feeds on fish and amphibians, but will take small mammals, rodents, birds, and even other reptiles. In captivity, they can be introduced to other types of food, as well.

Venom

The posterior maxillary teeth of ''H. gigas'' are enlarged, and the

Duvernoy's gland The Duvernoy's gland is a gland found in some groups of '' colubrid'' snakes. It is distinguished from the venom gland and is not found in '' viperids'' or ''elapids''. It was named for French zoologist Georges Louis Duvernoy who first describe ...

produces a secretion with high

proteolytic Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called protease ...

activity. Besides the ability of this large and powerful snake to inflict mechanical trauma, numerous cases of local envenomation and perhaps hypersensitivity have occurred, most of which have gone unreported. Prolonged, chewing bites may result in painful (sometimes extensive and persistent) swelling, as well as bruising. Nevertheless, the species is regularly kept as a pet, becoming increasingly popular in recent years. Manning et al. (1999) described a case in which an 18-year-old male pet-store employee was bitten on the wrist by a specimen that hung on for 1.5 minutes. Some mild swelling resulted, but after nine hours, the victim claimed to have experienced three bouts of muscle paralysis, during which he fell and was unable to move or speak, but a medical examination did not produce any unusual results. The symptoms described possibly were the result of anxiety. The liquid venom yield ranges from 0-50 microliters and the solid venom yield is 1.3 mg.

Taxonomy

This species was once considered to constitute a single monotypic genus, ''Cyclagras'' Dowling HG, Gibson FW (1970). "The relationships of the Neotropical snakes ''Hydrodynastes bicinctus'' and ''Cyclagras gigas'' ". ''Herpetological Review'' 2 (2): 37-38.

References

External links

* {{Taxonbar, from=Q431664 Colubrids Snakes of South America Reptiles of Argentina Reptiles of Bolivia Reptiles of Brazil Reptiles of Paraguay Fauna of the Pantanal Taxa named by Gabriel Bibron Taxa named by André Marie Constant Duméril Taxa named by Auguste Duméril Reptiles described in 1854