Wild About Illinois Snakes!

Forty species of snakes inhabit Illinois, dwelling in forests, grasslands, marshes, swamps, ponds, lakes, streams, rivers and sloughs. Some species are quite common, while others are very rare. These reptiles are solitary predators that eat a variety of prey. Snakes have interesting structural features including the Jacobon's organ, which is used to detect odors. They lack legs, ear openings and eyelids. Four species of Ililnois snakes, the eastern copperhead (Agkistrodon contortrix), the northern cottonmouth (Agkistrodon piscivorus), the timber rattlesnake (Crotalus horridus) and the eastern massasauga (Sistrurus catenatus) are venomous. The chief conservation concerns for Illinois snakes are habitat alteration and loss and over-exploitation for the pet trade. Misinformation, lack of information and irrational fears have also affected snake populations.

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​Click on the family name to see the gallery! Different images may be available on the species page as well as the attached PDF.

Kingdom: Animalia - Animals are multicellular organisms that rely on other organisms for nourishment. There cells do not have cell walls. Most animals are capable of movement at least in some portion of their life cycle. Reproduction is generally sexual, but in some animals asexual reproduction may be utilized at certain times.
Phylum: Chordata - The Phylum Chordata contains the vertebrate animals. Mammals, birds, reptiles, amphibians and fishes are included in this phylum. These animals have a notochord at some point in their development. They have a tubular nerve cord along the back. Gill slits and a tail are present at some point in their life cycle. They have an internal skeleton.
Class: Reptilia (lizards, snakes and turtles) - These organisms develop from and amniotic egg, which is either deposited on land or retained within the female for the extent of its development. The egg provides everything the embryo needs to develop. The shell of a reptile egg is leathery. Fertilization is internal. Reptiles are covered in scales, and their skin is dry.
Order: Squamata (lizards and snakes) - The lizards and snakes have dry, scaly skin. Their lower jaw is attached by a special bone that allows the mouth to open very wide.

Family: Colubridae - The family Colubridae is the largest family of snakes in the world. Because of the great number of species found in this category, it is difficult to find characteristics that are common to all of its members. Three features that they have in common are no pelvic girdle, no functioning left lung and the head covered by large scales. All of the colubrid snakes in Illinois lay eggs and are harmless to humans.
     scarletsnake (Cemophora coccinea)
     North American racer (Coluber constrictor)
     coachwhip (Coluber flagellum) [state endangered]
     prairie kingsnake (Lampropeltis calligaster)
     eastern kingsnake (Lampropeltis getula)
     milksnake (Lampropeltis triangulum)
     rough greensnake (Opheodrys aestivus)
     smooth greensnake (Opheodrys vernalis)
     Great Plains ratsnake (Pantherophis emoryi) [state endangered]
     western foxsnake (Pantherophis ramspotti)
     gray ratsnake (Pantherophis spiloides)
     eastern foxsnake (Pantherophis vulpinus)
     gophersnake (Pituophis catenifer) 
     flat-headed snake (Tantilla gracilis) [state threatened]

Family: Crotalidae - These are the venomous snakes including the rattlesnakes, copperhead and cottonmouth that are found in Illinois. These “pit vipers” have a pit on each side of the head that detects infrared radiation to help them locate warm-blooded prey at night. They also have a pair of fangs in the front of the mouth, a triangular-shaped head and an elliptical pupil in the eye. They give birth to live young.
     eastern copperhead (Agkistrodon contortrix)
     northern cottonmouth (Agkistrodon piscivorus)
     timber rattlesnake (Crotalus horridus) [state threatened]
     eastern massasauga (Sistrurus catenatus) [state endangered and federally threatened]

Family: Dipsadidae - The members of this family are generally small snakes that have teeth in the back of the jaw that are used to transfer venom into their prey. They lay eggs and are harmless to humans.
     common wormsnake (Carphophis amoenus)
     western wormsnake (Carphophis vermis)
     ring-necked snake (Diadophis punctatus)
     red-bellied mudsnake (Farancia abacura)
     western hog-nosed snake (Heterodon nasicus) [state threatened]
     eastern hog-nosed snake (Heterodon platirhinos)

Family: Natricidae - These snakes can be found in a variety of habitats, although many of them live near water. They give birth to live young. The scales are keeled (ridged), although the keels in some species may be difficult to detect. They are harmless to humans.
     Kirtland’s snake (Clonophis kirtlandii) [state threatened]
     Mississippi green watersnake (Nerodia cyclopion) [state threatened]
     plain-bellied watersnake (Nerodia erythrogaster)
     southern watersnake (Nerodia fasciata) [state endangered]
     diamond-backed watersnake (Nerodia rhombifer)
     common watersnake (Nerodia sipedon)
     Graham’s crayfish snake (Regina grahamii)
     queensnake (Regina septemvittata)
     DeKay’s brownsnake (Storeria dekayi)
     red-bellied snake (Storeria occipitomaculata)
     western ribbonsnake (Thamnophis proximus)
     plains gartersnake (Thamnophis radix)
     eastern ribbonsnake (Thamnophis sauritus) [state threatened]
     common gartersnake (Thamnophis sirtalis)
     lined snake (Tropidoclonion lineatum) [state threatened]
     smooth earthsnake (Virginia valeriae)

​Four native Illinois snake species are venomous: the copperhead, cottonmouth, timber rattlesnake and the massasauga. 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.

Photo © Scott Ballard - The head of a timber rattlesnake 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. 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.

​​Snakes, like all reptiles, have a scale-covered body. The dry scales reduce moisture loss through the skin. Depending upon the species, scales are either keeled or smooth. Snakes do not have eyelids. Each eye is covered with a clear, hard scale. The snake's tongue is used in the sense of smell. By flicking its forked tongue out of the mouth, a snake can pick up chemical particles from the air around it. When the tongue is pulled back into the mouth, the fork tips are placed into the Jacobson's organ, located in the front part of the roof of the mouth. The snake detects odors by analyzing the particles with its nervous system. The sense of smell is important to this animal for recognizing prey, enemies and a mate. Snakes have teeth that are curved toward the back of the mouth so that prey items cannot easily escape once they are in the mouth. The lower jaws are movable which allows the snake to take in large food items.

Snakes do not have legs, yet they can move quickly and easily in a variety of habitats. Their flexible movements are the result of their reduced skeletal system, which is composed of a skull, many vertebrae and many ribs. The skeletal and muscular systems, along with the platelike scutes on the belly, work together to allow a snake to move swiftly, pushing off of surface irregularities in the places it crawls.

The male snake has paired reproductive organs called hemipenes stored in the base of the tail, one part along each side. They are used to transfer sperm to the female. Only one hemipenis is used at any time, and the one used depends on which side of the female's body the male snake is crawling along.

​Illinois snake species hibernate during the cold winter months, becoming active in spring as temperatures and day length increase. Snakes are cold-blooded and can be seen basking in the sun on logs or other objects. They are generally active during the day, but they can become nocturnal when summer temperatures rise. Snakes are solitary predators. They use their sense of smell to track prey items. Once encountered, the prey is either overpowered, constricted or injected with venom to subdue it, and then swallowed whole. After feeding, the snake seeks out a place to hide until the prey is digested. Snakes eat a variety of prey including invertebrates, fishes, lizards, birds, rats, mice and other small mammals. Some snakes even eat other snakes.

Although the snake's body grows throughout its life, its outer skin layer does not. The snake must shed its old skin to allow the new skin layer underneath to continue growing. At this time, the body produces a milky-blue fluid that separates the two layers of skin, which causes the clear scales over the eyes to become milky in appearance and the overall color of the snake to be drab. After a few days, the eye scales become clear and the snake begins rubbing its head on rough objects to loosen the skin. It then crawls out of the old skin. Snakes shed their skin two to four times per year depending on how much they eat. The shed skin is usually turned inside out.

Photo © Scott Ballard - A copperhead sheddings its skin. Notice the bright pattern on the snake where the old skin has peeled away.

Snakes come together in the spring and fall for mating. Spring matings result in young born or hatched in the late summer or early fall of the year. If a female mates in fall, she will store the sperm in her body until spring. If she does not encounter a male in the spring, she can still produce young using the stored sperm. Snakes are either oviparous, ovoviviparous or viviparous. Oviparous snakes lay leathery-shelled eggs in late May and June. The eggs are placed in moist, warm areas such as rotting logs and stumps. The young have a small egg tooth on the snout that enables them to cut through the shell. After hatching, the egg tooth falls off. Ovoviviparous and viviparous snakes retain the developing embryos in their body until late summer. Their young are born live in thin, transparent membranes from which they emerge. Snakes do not exhibit parental care for their young. Young snakes live for a few days on yolk stored in their stomach before seeking their own prey.

Photo © Scott Ballard - Recently hatched snake eggs in moist, rotting wood. 

​Eleven Illinois snake species are listed (as of 2020) as either state endangered or state threatened. Endangered Illinois snakes include the coachwhip, the southern watersnake, the massasauga, and the Great Plains ratsnake. Illinois threatened snakes include Kirtland's snake, the timber rattlesnake, the plains hog-nosed snake, the Mississippi green watersnake, the flat-headed snake, the eastern ribbonsnake and the lined snake. Several of these species are at the edge of their geographic range in Illinois, occurring in only a few counties and having never been present in large numbers. Kirtland's snake, the massasauga and the timber rattlesnake, however, are sharply declining over a large area of the United States.

Habitat alteration and loss are major factors in the declining populations of snake species. Many people do not consider snakes beneficial and are not concerned about destroying the forests, grasslands, swamps and sloughs where snakes. Another factor is the illegal trade of reptiles in Illinois. There are several laws designed to protect all native Illinois snake species. However, selling reptiles can be profitable and is tempting to some people even though it is illegal. Killing of snakes because of misinformation, lack of information and irrational fears has also affected populations. Habitat preservation, law enforcement and education are the keys to conserving Illinois snakes.

The eastern massasauga, a rattlesnake species, is endangered in Illinois.

bask - to expose the body to the direct rays of the sun (e.g., snakes may be seen basking on rocks or logs)

cold-blooded - having a body temperature that varies with that of the environment

constriction - method used by some snakes to kill prey by coiling tightly around the prey item to prevent it from breathing

endangered species - a species in danger of becoming extinct within all or part of its range

hemipenis; hemipenes (pl.) - paired organ in male snakes used to transfer sperm to the female in sexual reproduction

hibernate - to become inactive during cold periods of the year

Jacobson's organ - chemically sensitive organ in the mouth that is used with the tongue to detect smells

juvenile - individual that has not attained sexual maturity

keel; keeled - raised ridge on the scales of the sides and back of some snakes

keratin - hard, tough, fibrous protein produced in the skin; the basic substance that makes up scales, claws, fingernails, and hair

oviparous - animals producing eggs that hatch outside the body of the female

ovoviviparous - species in which the eggs develop and hatch inside the female's body

pit viper - a venomous snake with a heat-sensing pit on each side of the head

scute - an enlarged scale on a reptile, such as that found on the belly of snakes

threatened species - a species likely to become endangered

venom - a poisonous secretion transmitted by a bite or a sting

venomous - secreting and transmitting venom

viviparous - species in which the young are born live after developing completely within the female's body

The smallest snake in Illinois is the flat-headed snake. The longest Illinois specimen measures eight inches (20.3 cm).

The largest Illinois snake is the gopher snake, with the Illinois record length at seven feet, two inches (218.5 cm).

A snake can swallow prey that is three times larger than the size of its own head.

Snakes are very efficient rodent controllers. Large and medium-sized snakes can eat up to nine pounds of rats and mice per year. That amount of rodents could fill a king-sized pillowcase!

Females of some snake species can store sperm for as long as five years inside their body.

Snake scales and rattlesnake rattles are made of keratin, a hard protein also found in the hair, fingernails and hooves of other animals.

Snakes have four rows of teeth in the top of the mouth and two rows on the bottom of the mouth.

Rattlesnakes add a new segment at the base of the rattle each time the snake sheds its skin. Old segments at the tip may disintegrate or break off.

Kingsnakes are immune to the venom of copperheads, cottonmouths, and rattlesnakes.

When threatened, a hog-nosed snake spreads its head and neck, somewhat like a cobra would, then rolls over and plays dead if it continues to be disturbed.

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