Cottonmouth Agkistrodon piscivorus - Endangered

Adult from Southeastern Missouri
Adult from Southeastern Missouri

Identification: Despite their scarcity (possibly absence) from the state, the infamous water moccasin is the subject of many embellished and fabricated snake stories in Indiana. Cottonmouths, while rather non-descript in coloration, have unique behaviors and a distinct form. Adult cottonmouths are robust and often uniformly dark on top with a broad, angular head and a broad, black stripe through their eye. Juveniles have dark-brown bands on a lighter brown background with a bright yellow-green tail tip that is used as a lure for prey. Adult cottonmouths grow to around three to four feet (0.9 - 1.2 cm) long, but some individuals may approach five feet (1.5 m) in length.

Similar Species: Without a doubt, many harmless northern watersnakes are killed annually because they were mistaken for water moccasins (cottonmouths). Unlike cottonmouths, watersnakes are widespread, abundant, and frequently encountered around lakes, ponds, rivers, and streams throughout the state. Diamond-backed watersnakes and plain-bellied watersnakes may also be mistaken for cottonmouths, where they occur, but all three of Indiana's harmless watersnakes have smaller heads and swim with only their head out of the water. Cottonmouths are buoyant and swim with their entire body on top of the water. They are even capable of coiling and remaining stationary on top of the water. Cottonmouths also have a broader head and tend to be uniformly dark as adults, where northern watersnakes and diamond-backed watersnakes have distinctive patterns. Juvenile cottonmouths can have a vibrant pattern, but have a bright yellow tail tip. Young cottonmouths are similar to copperheads, but are darker shades of brown and have a broad black stripe through the eye that copperheads lack.

All four of Indiana's venomous snakes have thick bodies, broad chunky heads, elliptical pupils, heat sensitive pits between the eyes and nostrils, and undivided post-anal ventral scales (under the tail). However, most of these characteristics require close examination, elliptical pupils can dilate and become round, and many non-venomous snakes (especially hog-nosed snakes) will broaden and flatten their heads in self defense. Therefore, it is always best to treat any snake that you cannot positively identify as potentially venomous. Venomous snakes are best left alone as most snake bites occur when someone attempts to handle or kill the snake. Snakes are not aggressive and do not hunt, attack, or chase people when left unmolested.

Distribution: Cottonmouths are known from only a single population in far southwestern Indiana (Dubois County) and have not been seen in the state in over ten years. As such, they are state endangered but it is likely that cottonmouths no longer occur in Indiana. Over twenty years ago, three cottonmouths were captured in Harrison County, but these snakes likely did not represent a breeding population and may have been translocated from elsewhere.

Lowland Stream in Southwestern Indiana
Lowland Stream in Southwestern Indiana

Distribution Map
Distribution map of Cottonmouth (Agkistrodon piscivorus)
Photographs