Identifying Illinois’ Venomous Snakes
Illinois is home to four native venomous snake species: the Copperhead, Cottonmouth (also known as Water Moccasin), Timber Rattlesnake, and Eastern Massasauga. All are pit vipers, possessing a heat-sensing pit between their eye and nostril that helps them detect prey.
Venomous snakes in Illinois share common features. They have a triangular-shaped head, noticeably wider than their neck, and elliptical pupils resembling a cat’s eye, unlike the round pupils of most non-venomous snakes. The Copperhead, for instance, has a copper-red head and a body that is red-brown or yellow-brown with distinctive hourglass-shaped markings.
The Cottonmouth is dark brown to black, sometimes displaying dim crossbands; younger individuals often have a yellow-tipped tail. Timber Rattlesnakes are gray, yellow, or greenish-white with jagged dark bands along their back and a prominent rattle. The Eastern Massasauga, Illinois’ smallest venomous snake, is gray or light brown with rows of dark blotches and a rattle that creates a buzzing sound.
Where Venomous Snakes Are Found
Illinois’ venomous snakes occupy specific habitats across the state. Copperheads are primarily found in the southern third of Illinois, particularly south of Route 16, and along the lower Illinois River valley. They favor upland forests, rocky hillsides, and river bluffs with limestone or sandstone outcroppings, often hiding under rocks or debris.
Cottonmouths are semi-aquatic, inhabiting swamps, marshes, and slow-moving water bodies in the southernmost tip of Illinois, south of Route 13. They can be found in various freshwater habitats, including streams and ditches, and are often active at night.
Timber Rattlesnakes are found in the southern fourth of the state, particularly in heavily timbered areas with rock outcrops and bluffs, and along the Mississippi and Illinois River valleys. They prefer dense forests and river floodplains, often using rock crevices for hibernation.
Eastern Massasauga Rattlesnakes, an endangered species in Illinois, are localized, found in scattered colonies across the state’s northern two-thirds. Their habitats include wetlands, bogs, wet prairies, and old fields, though they may move to drier areas in summer.
Encountering and Responding to Venomous Snakes
Encounters with venomous snakes in Illinois usually result from accidental disturbance, not aggressive pursuit. If a snake is seen, maintain a safe distance of at least six feet. Avoid provoking, handling, trapping, or killing the snake, as most bites occur during intentional interaction. Allowing the snake to move away on its own is the safest approach.
If a snakebite occurs, seek immediate medical attention by dialing 911 or going to the nearest emergency department. While waiting for help, remain calm, as panic can increase heart rate and potentially speed venom circulation. Remove any jewelry or tight clothing near the bite area in anticipation of swelling.
Keep the bitten limb immobilized and positioned at or slightly below the level of the heart. Gently clean the wound with soap and water, then cover it with a clean, dry dressing.
- Do not apply a tourniquet.
- Do not cut the wound.
- Do not attempt to suck out venom.
- Do not apply ice, as these actions can cause more harm.
To prevent encounters, wear appropriate footwear in snake habitats, avoid reaching into concealed areas like rock crevices or dense brush, and be aware of your surroundings.