The question of whether the water moccasin, also known as the Cottonmouth, is found in Missouri is a common query. The short answer is yes, the venomous snake (Agkistrodon piscivorus) is a native species of Missouri. As a pit viper, this semi-aquatic snake is a recognized part of the state’s natural fauna. Its presence is not widespread across all regions, but understanding its distribution and characteristics is important for safety.
The Definitive Answer: Presence in Missouri
The Cottonmouth’s distribution in Missouri is highly restricted, marking the northwestern limit of the species’ range in North America. The snake is most commonly found in the lowlands of the southeastern corner of the state, particularly within the Mississippi Lowlands region, which includes the Bootheel area. Within this region, they inhabit cypress swamps, sloughs, oxbow lakes, and drainage ditches where water is slow-moving or stagnant.
In addition to the southeastern lowlands, localized and scattered populations of Cottonmouths can be found in the Ozark region. These Ozark populations are often associated with rocky, cool, spring-fed creeks and small rivers. The presence of this snake is not statewide, and natural populations are not known to exist north of the Missouri River, primarily due to the limiting factor of low winter temperatures. The restricted range means that most aquatic snakes encountered in Missouri are non-venomous species.
Identifying Features of the Cottonmouth
The Cottonmouth has physical and behavioral traits that distinguish it from harmless aquatic snakes. As a heavy-bodied pit viper, the adult snake is typically dark olive, brown, or nearly black, with crossbands that often become indistinct with age. A key morphological feature is its large, distinctly triangular or blocky head, which is noticeably wider than its neck.
Another defining characteristic is the vertical, cat-like pupil of its eye, a trait shared by all Missouri pit vipers. The snake also has a deep, heat-sensing facial pit located between its eye and nostril. When threatened, the Cottonmouth exhibits a characteristic defensive posture, coiling up and throwing its head back to display the bright white, cotton-like lining of its mouth, which is the source of its common name.
Non-Venomous Look-alikes
Many people mistake the non-venomous Northern Water Snake (Nerodia sipedon) for the Cottonmouth, largely because both species inhabit similar aquatic environments. The Northern Water Snake is abundant throughout the state and also has a dark body with crossbands, leading to frequent misidentification. However, the Northern Water Snake has a more slender body, a rounded head that is not distinctly wider than its neck, and round pupils.
A crucial difference is the swimming posture; the Cottonmouth often swims with its entire body floating on the surface, while the Northern Water Snake typically swims with only its head above the water. Furthermore, when defensively provoked, the Northern Water Snake may flatten its head and body to appear more threatening, but it lacks the facial pits and the bright white mouth display of the Cottonmouth. Other non-venomous aquatic snakes in Missouri, like the Plain-bellied Water Snake, are also harmless.
Safety and Encounter Prevention
When entering areas known to harbor Cottonmouths, such as wetlands and river bottoms, simple precautions minimize the risk of an encounter. Wearing protective footwear, specifically boots at least 10 inches high, is recommended when walking in dense vegetation or near water. Individuals should be mindful of where they place their hands and feet, avoiding reaching into dark crevices, under logs, or into brush piles.
If a Cottonmouth is sighted, the safest action is to maintain a distance and allow the snake to retreat. These snakes will typically try to escape if cover is nearby, and they only bite when they feel threatened or are deliberately provoked. If a bite occurs, seek immediate medical attention; the venom can cause severe tissue damage, and timely treatment with antivenom is necessary.