Illinois is home to approximately 40 snake species. While most are harmless and beneficial, four native species are venomous. Understanding which snakes are venomous and how to identify them can help ensure safety.
Illinois’ Venomous Snake Species
Illinois is home to four venomous snake species: the Eastern Copperhead, Northern Cottonmouth, Timber Rattlesnake, and Eastern Massasauga Rattlesnake. All are pit vipers, meaning their venom primarily affects the blood, causing tissue damage.
The Eastern Copperhead (Agkistrodon contortrix) is found in the southern two-thirds of Illinois, particularly in upland forests, rocky hillsides, and river bluffs. This snake typically measures 24 to 36 inches long and has a distinctive copper-red head. Its body displays pale brown to pinkish-brown coloration with hourglass-shaped, reddish-brown crossbands.
The Northern Cottonmouth (Agkistrodon piscivorus), also known as the Water Moccasin, is restricted to the swamps and wet bottomlands of extreme southern Illinois. These semi-aquatic snakes average 30 to 42 inches in length and can appear plain black or brown, though some have faint crossbands. When threatened, they may open their mouths wide, revealing a stark white interior, which gives them their common name.
The Timber Rattlesnake (Crotalus horridus) inhabits the southern one-fourth of Illinois, favoring heavy timber with rock outcrops and bluffs. Adults typically range from 36 to 60 inches long and have a broad, flattened head. Their bodies are often gray, yellow, or green-white with dark, jagged crossbands and sometimes a rust-colored stripe down the back.
The Eastern Massasauga Rattlesnake (Sistrurus catenatus) is a smaller rattlesnake, averaging 18 to 30 inches, and is considered endangered in Illinois. It is found in scattered locations within prairie wetlands and river floodplains across the state. This snake has a gray or light brown body with rows of dark brown or gray blotches along its back and sides.
Distinguishing Venomous from Non-Venomous Snakes
Identifying venomous snakes in Illinois involves recognizing characteristics common to pit vipers. These features help distinguish them from the many harmless species.
One notable feature is their triangular or spade-shaped head, due to venom glands behind the eyes, contrasting with the more slender, oval heads of many non-venomous snakes. However, some non-venomous snakes can flatten their heads when threatened, mimicking this appearance.
Another distinguishing characteristic is their vertical, elliptical pupils, similar to a cat’s eye, while most non-venomous snakes have round pupils. Additionally, pit vipers have a heat-sensing pit on each side of the head, between the eye and nostril, which is absent in non-venomous species.
Examining the scales on the underside of the tail can also provide clues. Venomous snakes typically have a single row of scales after the vent, whereas non-venomous snakes usually have a double row.
Safe Practices Around Snakes
Exercising caution can help prevent unwanted encounters in areas where snakes might be present. Always observe snakes from a distance and never attempt to handle, harass, or capture them. Most snake bites occur when individuals try to interact with a snake directly.
Being aware of your surroundings in snake habitats, such as tall grass, rocky areas, or near water, is important. Wearing sturdy shoes and long pants when hiking can offer protection. For residential areas, keeping grass trimmed, weeds at bay, and covering wood or debris piles can reduce places where snakes might hide. If a snake is encountered, allow it to move away on its own, as venomous snakes prefer to avoid confrontation and will typically flee.