Missouri is home to over 40 species of snakes, but only four possess venom that poses a threat to human health. The state’s four venomous snakes are all classified as pit vipers. This group is characterized by their ability to sense heat from warm-blooded prey using specialized facial pits located between the eye and nostril. This article helps residents and visitors identify these snakes, understand where they live, and know the correct actions to take in the event of an encounter.
Identifying Missouri’s Four Venomous Snakes
All four of Missouri’s venomous species share the general pit viper characteristics, including a broad, triangular-shaped head and pupils that appear as vertical slits, similar to a cat’s eye in bright light. Beyond these common features, each species has unique visual cues that aid in identification.
The Northern Copperhead (Agkistrodon contortrix) is the most commonly encountered venomous snake in the state and is recognizable by its distinctive coloration. Its body is a pinkish-tan to light brown, overlaid with dark brown crossbands that are narrow along the spine and wide on the sides, creating a pattern often described as an hourglass or bow tie. Adults typically reach lengths between two and three feet.
The Western Cottonmouth (Agkistrodon piscivorus) is a heavy-bodied, semi-aquatic snake. Adults are usually dark, ranging from olive-brown to almost solid black, often obscuring the dark crossbands visible on younger snakes. When threatened, the cottonmouth performs a unique defensive display, opening its mouth wide to reveal the strikingly white, cotton-like interior, which gives the species its common name.
Missouri’s largest venomous snake is the Timber Rattlesnake (Crotalus horridus), which can grow up to five feet long and is easily identified by the segmented keratin rattle at the end of its tail. Its body color varies from yellow or tan to gray, marked with dark, V-shaped crossbands that form chevrons along its back. The tail of an adult is typically black or dark brown.
The Massasauga (Sistrurus catenatus) is a much smaller rattlesnake, rarely exceeding two to three feet in length. Unlike the Timber Rattlesnake, the Massasauga has nine large, plate-like scales on the top of its head, a distinguishing feature of its genus. The body is light gray or brown with a row of dark brown blotches running down the center.
Where These Snakes Live in Missouri
The distribution of Missouri’s venomous snakes is closely tied to their preferred habitat types, with some being widespread and others highly localized. The Northern Copperhead is found throughout the entire state, preferring wooded hillsides, rocky outcrops, and riparian zones near streams. They are highly adaptable and often found near human development, especially where there is leaf litter or debris for cover.
The Western Cottonmouth has the most restricted range, being primarily confined to the southeastern lowlands of Missouri, which contain extensive swamps and sloughs. As semi-aquatic snakes, they are rarely found far from standing water, such as sluggish streams, marshes, or ponds. Their presence in the Ozarks is rare.
Timber Rattlesnakes are distributed across the state, though their populations are patchy due to habitat loss. They favor dense forests and rocky, rugged terrain, particularly in the Ozark region. They utilize rock crevices and bluffs as den sites for hibernation, moving away from these dens to forage in surrounding woodlands during warmer months.
The Massasauga is the most localized and rare of the four, with populations restricted mainly to prairie remnants and low-lying, swampy areas in the northern and north-central parts of the state. Because of its specific habitat requirements and small population size, encountering a Massasauga is exceptionally uncommon.
Reducing Encounters and Understanding Harmless Species
The most effective way to avoid a snake bite is to recognize where they hide and take precautions when outdoors. Wearing long pants and sturdy, high-top leather boots offers protection when hiking through brush or tall grasses. People should avoid placing their hands or feet in areas they cannot see, such as under logs, rocks, or piles of debris.
Many encounters happen when non-venomous species are mistakenly identified. Harmless snakes in Missouri, like the Northern Water Snake and the Prairie Kingsnake, are often misidentified as the venomous Cottonmouth or Copperhead. A reliable distinguishing feature is the shape of the pupil: non-venomous species have round pupils, while all pit vipers have vertical, slit-like pupils.
Non-venomous snakes typically have a more slender body profile and a head only slightly wider than their neck, lacking the distinct triangular shape of pit vipers. The Northern Water Snake, for example, is often mistaken for the Cottonmouth, but it has a round pupil and usually flees into the water. The Prairie Kingsnake, which has dark, rounded markings, is often confused with the Copperhead, but lacks the characteristic hourglass pattern.
Immediate Steps Following a Bite
If a bite from a venomous snake is confirmed or suspected, the most important action is to seek medical attention immediately. Call 911 or emergency services right away to ensure transport to a medical facility equipped with antivenom. While waiting for help to arrive, the victim should remain as calm as possible to slow the spread of venom through the body.
The affected limb should be immobilized and kept at or slightly below the level of the heart, if possible. Any restrictive clothing or jewelry, such as rings or watches, should be removed from the affected area before swelling begins.
Avoid all traditional but ineffective first aid techniques, as they often cause more harm than good. Do not attempt to cut the wound, suck out the venom, apply a tourniquet, or use ice. These actions can concentrate the venom, increase tissue damage, or cause severe injury to blood vessels, making recovery more difficult.