Bruce Rauner, Governor

DNR Links Skip to Content Skip to State Links

 IDNR Home
 Agency Offices
 Disabled Outdoors
 Freedom of Information Act
 Get Involved
 Grant Info
 Great Lakes Restoration
 License / Permit / Register
 Kids & Education
 Law Enforcement
 Mandatory Safety Programs
 Lodges / Leasing
 More Links
 Outdoor Recreation
 Parks & Recreation
 Press Releases
 State Museums
 World Shooting & Recreational Complex
 DNR A to Z



Venomous Snakes

Four native Illinois snake species are venomous: the copperhead (Agkistrodon contortrix), the cottonmouth (Agkistrodon piscivorus), the timber rattlesnake (Crotalus horridus), and the eastern massasauga (Sistrurus catenatus). Venom is a toxin for subduing prey. It is delivered through a pair of hollow fangs in the front, upper mouth that fold up when the mouth is closed and drop into place when the snake bites. The fangs are shed and replaced periodically. Venomous snakes strike, inject venom, then pull away. They find and eat the prey after it dies. Illinois' venomous snakes produce venom that affects the blood of the prey. Juvenile snakes have venom equal in potency to that of the adult, but they produce lesser amounts.

Illinois' venomous snakes are pit vipers, having a large opening, or "pit," on each side of the head between the eye and nostril. It is used to detect heat emitted by potential warm-blooded prey. Besides the pit, venomous snakes can be recognized by the elliptical pupil in the eye. With the exception of the timber rattlesnake, the tip of the tail is bright yellow in all juvenile Illinois venomous snakes.


The head of a timber rattlesnake (Crotalus horridus) shows the characteristics of a pit viper. Note the elliptical pupil in the eye and the heat-sensing pit, which is seen just above the upper lip, between the eye and the nostril.

Venomous snakes tend to be restricted to specific habitats. Copperheads occur in the southern one-third of Illinois, south of Route 16, and in the lower Illinois River valley. They prefer upland forests or river bluffs with limestone or sandstone outcroppings. Cottonmouths live in swamps and wet bottomlands in southern Illinois, south of Route 13. Timber rattlesnakes may be found in the southern one-fourth of the state (south of Interstate 64), in the lower Illinois River valley, in the Mississippi River valley and in a few other locations. These snakes prefer heavy timber with rock outcrops and bluffs. Eastern massasaugas live in scattered locations within the counties of Madison, Clinton, Piatt, Knox, Warren, Will, Cook, and Lake. Their habitats are prairie wetlands and river floodplains.

While venomous snakes are not aggressive and tend to bite people only when stepped on, picked up, or cornered, their bite is a serious matter. Even freshly killed snakes can bite. These snakes should be avoided and precautions taken (wear leather boots, do not reach under rocks or logs, do not step over rocks or logs, look around before you sit) if you are entering an area possibly inhabited by venomous snakes. Although usually not deadly, the bite is painful and can cause swelling, nausea, and the risk of infection. If you are bitten, go to a hospital for treatment immediately.

Click image to return to Table of Contents

Kids & Education

 New This Month
 Online Order Form
 Student Pages

Copyrightę 2015 Department of Natural Resources
Accessibility    Contact    FAQs    Podcasts    Privacy    Social Networking