Northern Cottonmouth Agkistrodon piscivorus - Endangered

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. Northern Cottonmouths, while rather non-descript in coloration, have unique behaviors and a distinct form. Adult Northern 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 Northern 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.

Adult from southeastern Missouri
Adult from southern Illinois

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 Northern 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. Northern 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. Northern 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 Northern Cottonmouths can have a vibrant pattern, but have a bright yellow tail tip. Young Northern Cottonmouths are similar to Eastern 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 Eastern 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.

The non-venomous watersnakes (Nerodia) are commonly confused with CotNorthern Cottonmouthsonmouths across their range, simply because they are snakes in water. Thus it is important to note that Northern Cottonmouths are only found in southernmost Midwest. Nerodia also lack the facial pits present in all pit-vipers. Juvenile Northern Cottonmouths may be mistaken for juvenile copperheads given similar patterning and yellow tipped tails.

Ecology and Conservation

The Northern Cottonmouth is semi-aquatic and inhabits a variety of wetland habitats including swamps, lakes, ponds, rivers and ditches. It has a broad diet consisting mainly of fish along with amphibians, small rodents, lizards, insects, and even other snakes. The Northern Cottonmouth is active primarily at night, but it may also be active during daylight hours during the spring and fall, especially at the southern extremity of its range. This species typically mates during late spring but may also mate in the fall before returning to hibernacula. The Northern Cottonmouth gives live birth to an average of seven young, generally during late fall or early summer.

The Northern Cottonmouth may often be seen basking near the edge of the water on logs, stumps, or overhanging branches. When approached, this relatively slow-moving snake will often hold its ground rather than flee. If threatened, it may vibrate its tail rapidly. If this threat display proves ineffectual, it may attempt to flee or throw its head in the air with mouth agape exposing the inner white lining (lower right image). It is this behavior that gives it the name “cottonmouth.”

The Western Cottonmouth is an endangered species in Indiana.

Lowland stream in southwestern Indiana
Lowland stream in southwestern Indiana

Distribution

Northern 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 Northern Cottonmouths no longer occur in Indiana. Over twenty years ago, three Northern Cottonmouths were captured in Harrison County, but these snakes likely did not represent a breeding population and may have been translocated from elsewhere.

Taxonomy

There are three subspecies of the cottonmouth. The Western Cottonmouth (A. p. leucostoma) is the only subspecies found in the Midwest. The term leucostoma refers to the white interior of mouth.

Literature Cited

Distribution Map
Distribution map of Northern Cottonmouth (Agkistrodon piscivorus)
Photographs