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The Largest Cottonmouth

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Also called water moccasins, the cottonmouth (Agkistrodon piscivorus) is a large, venomous pit viper native to the southeastern United States. This semi-aquatic reptile comes by its name because of its distinctive behavior of coiling and widely opening its mouth -- which is white -- when it senses danger. While normally around 3 to 4 feet long, they can grow much larger.


Juvenile cottonmouths have distinctive banding and are usually reddish-brown with a bright yellow tail. Adult snakes have a dark banded pattern which is sometimes not noticeable. The heads are broad and triangular with elliptical pupils, and there are two pits -- one between each eye and nostril -- that serves as a heat-sensing organ to help the snake find and identify prey. As water snakes, they have keeled -- or rough -- scales.


Three subspecies are recognized, based on geographic range and small differences in markings, with an overlap region in the central habitat range. The eastern cottonmouth is found in Virginia and North and South Carolina. Adults are often completely dark. The western cottonmouth lives primarily from Texas east to Georgia and north to southern Missouri and Kentucky. It can be black or brown with little or no pattern. The Florida cottonmouth inhabits south Florida up to southern portions of Georgia and South Carolina. This subspecies usually retains head markings into adulthood.


The western subspecies is the smallest cottonmouth, while the Florida cottonmouth is generally the largest. Overall, these snakes normally range from 2 to 4 feet in length, but specimens of 5 to 6 feet are not uncommon. The longest cottonmouth on record was an eastern cottonmouth that measured 74 inches. The snake was reportedly caught in a swamp near the Virginia-North Carolina border. Given to the Philadelphia Zoo, it soon died from injuries. Average weight of these snakes is 3 to 4 pounds.


Regardless of size, the venom of cottonmouths is dangerous and can be deadly. This snake is sometimes described as aggressive, due to the typical way it coils and opens its mouth when it senses danger. Still, it will slither the other way if given a chance. The venom is hemotoxic, meaning it destroys blood cells and associated tissue, along with reducing blood coagulation. If bitten, the victim should seek immediate medical care at a facility experienced in treating snakebites.