Illinois is home to a variety of snake species, including four native venomous ones. Understanding how to identify them can help ensure safety when encountering wildlife.
Venomous Snake Species in Illinois
Four native venomous snake species inhabit Illinois: the Eastern Copperhead, Northern Cottonmouth, Timber Rattlesnake, and Eastern Massasauga.
The Eastern Copperhead (Agkistrodon contortrix) measures 24 to 36 inches long, sometimes up to 4 feet. It has a copper-red head and a reddish-brown or yellowish-brown body with dark, hourglass-shaped crossbands. These bands are narrower across the back and wider on the sides.
The Northern Cottonmouth (Agkistrodon piscivorus), also known as water moccasin, is a semi-aquatic snake measuring 30 to 48 inches long. Its body can be plain black or brown, sometimes with faint crossbands, and it may display a dark stripe from its snout through the eye. Young cottonmouths often have a yellow-tipped tail.
The Timber Rattlesnake (Crotalus horridus) measures 36 to 60 inches long, sometimes up to 5 feet. Its body coloration can vary from gray, yellow, or greenish-white, featuring dark, often chevron-shaped, crossbands along its back. A rust-colored stripe might be present down the middle of its back.
The Eastern Massasauga (Sistrurus catenatus) is a smaller rattlesnake, measuring 18 to 30 inches long. It has a gray or light brown body with rows of dark brown or black blotches on its back and sides. Like other rattlesnakes, it possesses a rattle at the tip of its tail.
Identifying Venomous Snakes
Identifying venomous snakes in Illinois involves recognizing common features shared by all four species, which are pit vipers. These snakes typically have a triangular-shaped head that appears wider than their neck.
Their pupils are vertically elliptical, while non-venomous snakes in Illinois generally have round pupils. Pit vipers also possess a heat-sensing pit located on each side of their head, between the eye and the nostril.
Rattlesnakes are identifiable by the presence of a rattle at the end of their tail. While some non-venomous snakes may vibrate their tails when threatened, only rattlesnakes have the distinct segmented rattle structure. Additionally, venomous snakes in Illinois have a single row of scales on the underside of their tail, whereas most non-venomous snakes have a double row.
Encountering and Coexisting with Snakes
Venomous snakes in Illinois inhabit specific environments, primarily in southern Illinois, though some species extend further north. Copperheads are found in upland forests and river bluffs with rock outcroppings. Cottonmouths prefer swamps and wet bottomlands. Timber Rattlesnakes live in heavily forested areas with rock outcrops and bluffs. Eastern Massasaugas inhabit wet prairies, bogs, and old fields, primarily in the northern two-thirds of Illinois.
The risk of being bitten by a venomous snake in Illinois is low, as these snakes are not aggressive and typically bite only when provoked, stepped on, or handled. To prevent encounters, remain on designated paths and avoid walking through tall grass, dense brush, or leaf piles where snakes might hide. Wearing appropriate footwear, such as thick leather boots, offers protection outdoors.
Look before placing hands or feet into unseen areas like under rocks or logs. Never attempt to handle, harass, or pick up any snake, even if it appears dead, as freshly killed snakes can still bite reflexively. Maintaining a safe distance allows snakes to move away naturally.
Responding to a Snake Bite
If a venomous snake bite occurs, immediate medical attention is necessary. Stay calm and move away from the snake to a safe distance. Panic can increase heart rate, which may hasten the spread of venom.
Call 911 or your local emergency number without delay. While waiting for medical help, remove any jewelry or tight clothing from the bitten limb before swelling begins. Wash the bite area gently with soap and water, then cover it loosely with a clean, dry dressing. Keep the bitten area still and, if possible, position it at or below the level of the heart to slow the venom’s circulation.
Do not attempt to cut the wound, suck out the venom, or apply a tourniquet; these actions can cause further harm or accelerate venom absorption. Do not apply ice or heat to the bite, and avoid consuming alcohol or caffeinated beverages. Attempting to capture or kill the snake is also not recommended, as this increases the risk of another bite.