Venomous Snakes of Illinois

Illinois is home to four dangerously venomous snake species. They’re listed below.

Eastern Copperhead (Agkistrodon contortrix)

Northern Cottonmouth(Agkistrodon piscivorus)

Timber Rattlesnake (Crotalus horridus)

Eastern Massasauga(Sistrurus catenatus catenatus)

Illinois is also home to a couple of venomous snake species that are not dangerous to humans. These are the Eastern Hognose snake and the Garter snake.

We will talk about all of these venomous snakes in the paragraphs below.

Pit Vipers

Rattlesnakes, Copperheads, and Cottonmouths belong to the venomous Viperidae family. Another name for these snakes is pit vipers. Pit vipers have heat-sensing pits between their nostrils and eyes. These pits are actually specialized organs that detect infrared radiation from prey animals. Pit organs enable pit vipers to strike their prey precisely, even in the dark. They are also able to detect body heat from about 1 meter away.

Pit vipers have hollow fangs connected to venom glands. They use their fangs to inject venom into their prey. This venom immobilizes the prey, making it easier for the snake to consume. They primarily consume small mammals, reptiles, amphibians, and small birds. These snakes play an important role in maintaining balance in rodent populations.

Eastern Copperhead

Scientific Name:	Agkistrodon contortrix
Description:	Adult copperheads are 20 to 37 inches (50 to 95 cm) long. Their bodies are coppery brown overlayed with dark brown hourglass blotches.
Habitat:	Deciduous forests, river bottoms, and rocky wooded hillsides.
Conservation Status:	Common and native to the southern third of Illinois.

The Copperhead population in Illinois was formerly divided into two subspecies. These were the Northern Copperhead and Southern Copperhead. However, DNA analysis shows little genetic difference between the two. Today the former Northern Copperhead, Southern Copperhead, and Osage Copperhead are taxonomically combined. The common name for these snakes is Eastern Copperhead. Their scientific name is Agkistrodon contortrix. Source

The Eastern Copperhead is a pit viper native to the eastern United States.

Copperheads are stout heavy-bodied snakes. Adult copperheads are 20 to 37 inches (50 to 95 cm) long.

Eastern Copperhead snakes have reddish-tan to grayish-tan bodies. Their bodies are overlaid with hourglass-shaped dark brown markings. Their triangular heads are proportionately large. The color of their head is dark coppery brown. This is the reason they have the name “Copperhead.”

Where Do Eastern Copperheads Live in Illinois?

Eastern Copperheads are found in the southern third of Illinois. They are found in deciduous forests, river bottoms, and rocky wooded hillsides.

Eastern Copperhead Behavior

Copperheads are dangerous because they use camouflage as their number one defense mechanism. In other words, these snakes choose to lie perfectly still rather than flee most of the time. Their camouflage helps them blend in with leaf litter and other ground debris.

When they feel threatened, they occasionally mimic the tail vibration of a rattlesnake. But, in most cases, they choose to lie perfectly still.

Most copperhead bites on humans occur when the person steps on or near the snake.

Wintertime Brumation

Snakes do not tolerate the cold weather in the winter months very well. They are ectotherms, which means they can not regulate their body temperature internally. Physiologically, ectotherms cannot hibernate. Yet, they go into a state of suspended animation called brumation for up to 6 months out of the year.

Copperheads winter underneath rocks, in hollow logs, and in fissures on rocky hillsides. An individual might brumate alone in some parts of their range. But copperheads tend to be social. In some areas, they congregate together in dens with other snakes through the winter.

In hilly terrain, south-facing slopes capture more radiant warmth from the sun. So, that is where these dens are generally located. The other snakes they den with are not necessarily just copperheads. Sometimes, they share their dens with other species of snakes. You may find a Timber Rattler, a Black Rat Snake, or an Eastern Black Racer sharing the same den with copperheads. These wintertime dens may hold up to 60 snakes.

What Do Copperheads Eat?

Copperhead snakes are opportunistic feeders. They eat insects, spiders, frogs, small animals, birds, and other reptiles.

How Dangerous Are Copperheads?

A Copperhead can bite and inject venom from the time they are newly born. Like most pit vipers, they have hemotoxic venom. 

Most copperhead bites are not life-threatening. On the other hand, any bite from this snake is a medical emergency and should be treated as such. Prompt medical attention increases the chance of a good outcome.

Copperhead bites can cause intense pain, shock, and swelling. Their bites also have the potential to cause blood in urine, tissue damage, and kidney failure.

An interesting study has found that Copperhead venom contains a protein called contortrostatin. Contortrostatin has been found to stop the growth of cancer cells in mice.

Northern Cottonmouth

Scientific Name:	Agkistrodon piscivorus
Description:	Northern Cottonmouth snakes are stout, muscular snakes that grow up to 3 feet (.91m) long. They have a dark body with few markings. Their mouth is white.
Habitat:	They favor wet habitats such as swamps, drainage ditches, slow-moving rivers, and lakes.
Conservation Status:	Common and native to southern Illinois.

Another common name for the Northern Cottonmouth snake is water moccasin. These are stout, muscular snakes that grow up to 3 feet (.91m) long. They look a little bit like rattlesnakes without the rattle on the tail. People also sometimes mistake them for common water snakes. This could be a dangerous mistake.

The Northern Cottonmouth has a dark brown to black body with few markings. The inside of their mouth is white, hence the name “cottonmouth.” When threatened, they will pose with their mouth open. They have cat-like pupils, which appear as narrow slits in the day, and at night, they have a round appearance.

The juvenile cottonmouth has a more clearly defined pattern than adults. Their patterning resembles that of a copperhead snake. They have darker bands, though, that widen toward the belly and narrow at the back.

Where Do Northern Cottonmouths Live in Illinois?

Cottonmouths are found in southern Illinois. They are one of the three venomous species of snakes in the Shawnee National Forest.

They are semi-aquatic snakes. They favor wet habitats such as swamps, drainage ditches, slow-moving rivers, and lakes. Interestingly, they can hold their breath underwater for up to an hour while hunting for prey. They commonly sun themselves on rocks or logs at the water’s edge. Cottonmouths sometimes venture overland. It’s not unheard of to see one far from any aquatic environment. See

What Do Northern Cottonmouths Eat?

These snakes prey on fish, freshwater crustaceans, amphibians, small mammals, and other reptiles. Cottonmouths sometimes congregate around drying wetland pools to feed on any trapped fish.

How Dangerous Are Northern Cottonmouths?

Cottonmouth snake venom is cytotoxic. This means it destroys body tissue. Northern Cottonmouth bites sometimes lead to the amputation of limbs. On rare occasions, death can occur. See

Timber Rattlesnake

Scientific Name:	Crotalus horridus
Description:	Adult Timber Rattlesnakes grow between 36 and 60 inches (.91 to 1.52m) long. Their bodies are yellowish-brown with a dark chevron pattern. They also have a rusty stripe down their backs. Their tails are dark brown or black.
Habitat:	Timber Rattlesnakes prefer wooded areas and hillsides with rocky outcroppings.
Conservation Status:	Timber rattlesnakes are listed as threatened in Illinois.

Timber Rattler and Canebrake Rattlesnake are both common names for the Timber Rattlesnake. Generally, in higher-elevation habitats, they are called Timber Rattlesnakes. On the coastal plain, though, they’re called Canebrake Rattlesnakes.

The average Timber Rattlesnake grows between 36 to 60 inches (.91 to 1.52m) long. However, there have been reports of them growing up to 7 feet (2.13m) long. See

These snakes vary in color. Their general base coloration is a yellowish-brown to grey-brown, though. They have a dark brown to black chevron pattern on their back and sides against a lighter base color. Moreover, they have a rusty to reddish stripe down their backs. Their tails are dark brown or black with a tan rattle. There are also melanistic timber rattlers. These are dark and sometimes almost entirely black. In the dark color morph of these snakes, the tail is also darker than the rest of the snake’s body.

Where Do Timber Rattlesnakes Live in Illinois?

Timber Rattlesnakes live in southern, west-central, and northwestern Illinois. Source The timbered bluffs overlooking the Mississippi River are Timber Rattlesnake habitat. They also live in the Shawnee National Forest.

Timber rattlesnakes are a threatened species in the state of Illinois. Their downfall is mainly habitat loss. But indiscriminate killing is also a factor.

What Do Timber Rattlesnakes Eat?

Timber rattlers prey on small mammals such as mice, rats, squirrels, and chipmunks. They also eat small birds, other reptiles, and amphibians.

These snakes are excellent climbers. In fact, timber rattlers have been found in trees at heights of more than 80 feet. Source

The experts have proven that timber rattlesnakes help control Lyme disease. This is because as they consume rodents, they’re also consuming ticks. A timber rattler will consume 2,500 to 4,500 ticks per year, depending on the location. See

Wintertime Brumation

As we discussed in the section on copperheads, snakes brumate in the winter. Brumation is a reptile’s version of hibernation.

Timber Rattlesnakes make wintertime dens in sheltered spots. They den underneath rocks and logs, as well as in fissures in rocky hillsides. An individual Timber Rattler might brumate alone in some parts of their range. But in other areas, they congregate in dens with other snakes through the winter.

Dens are usually placed on slopes facing south because they get more warmth from the sun. They don’t always share their dens only with Timber Rattlers. Sometimes, they share their dens with other species of snakes. These might include Copperheads, Black Rat Snakes, and Eastern Black Racers. These wintertime dens may hold up to 60 snakes. Source

How Dangerous Are Timber Rattlesnakes?

Timber Rattlesnakes are among the most dangerous snakes in North America. This is due to their long fangs and high venom yield. 1% to 10% of untreated Timber Rattlesnake bites result in a fatality.

Fortunately, 40% to 60% of the time, they produce dry bites. In other words, although their fangs penetrate the body, they do not inject any venom. Source

These snakes produce hemotoxic venom. Timber Rattlesnake bites sometimes cause serious complications. These include shock, seizures, coma, internal bleeding, and deep tissue damage. Source

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Also see:

Scorpions in Illinois – Krebs Creek

Wild Cats in Illinois – Krebs Creek

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Eastern Massasauga Rattlesnakes

Scientific Name:	Sistrurus catenatus
Description:	Adult Eastern Massasaugas average 22 to 30 inches (55 to 75cm) long. Their body is light grey with dark brown blotches.
Habitat:	Swampy or marshy areas near lakes or streams.
Conservation Status:	Endangered in Illinois

The Eastern Massasauga rattlesnake grows to a length between 22 to 30 inches (55 to 75cm). Their body is a light gray with dark brown blotches. They also have a dark stripe on each side of their face and across their eye.  Some melanistic snakes are almost entirely black in color.

Massasaugas have a high-pitched rattle sound, which is different from other rattlesnakes. This is why they have the nickname Buzztail.

Where Do Eastern Massasauga Rattlesnakes Live in Illinois?

Eastern Massasaugas live in the northern two-thirds of Illinois. They live in forested swamplands, marshy grasslands, lake edges, wet prairies, and woodlands.

Eastern Massasaugas are endangered in Illinois. The Illinois Department of Natural Resources has this to say on the subject. “The endangered status of the eastern Massasauga is mainly due to habitat loss.” Drainage of prairie marshes has destroyed most of their former habitat in Illinois. Today, there are less than ten known Massasauga populations in the state.

What Do Eastern Massasauga Rattlesnakes Eat?

Eastern Massasaugas prey on smaller rodents such as mice and voles. They also eat frogs, toads, and small snakes.

How Dangerous Are Eastern Massasauga Rattlesnakes?

The venom of the Massasauga rattlesnake is cytotoxic. Cytotoxic venom destroys body tissue. Moreover, digestive enzymes in cytotoxic venom disrupt blood flow and prevent clotting. Massasauga bites to humans are rare. However, they do occur.

There are two documented deaths in Ontario from Eastern Massasauga envenomations. In each case, the victim did not receive antivenom in time. Source

Symptoms of Venomous Snake Bites

Some of the symptoms you may experience when a venomous snake bites you include:

• Discoloration in the area of the bite.
• Swelling in the area of the bite.
• Loss of muscle coordination.
• Tingling sensation in the area of the bite.
• Feeling nauseous.
• Having a faster heartbeat or rapid pulse.

What Should You Do if You Are Bitten?

If you or someone you are with has suffered a venomous snakebite, time is of the essence. Because the sooner a victim receives antivenom, the less chance the venom in their body has to cause harm. In other words, it is important to seek immediate medical treatment.

Do not attempt to kill the snake for identification purposes. This gives the snake a chance to bite you again. Also, consider that severed snakeheads can still bite and envenomate and often do. If you have a phone, take a picture of the offending reptile. Otherwise, get started on your way to the nearest hospital.

First Aid for Snake Bite Victims

• Remain calm and limit your movements. Do not run. If you must hike back to a vehicle, do it calmly and deliberately. Put as little stress on your heart as possible.
• Keep the area of the snake bite below the heart level and never above the heart level. Keeping the bite below the heart level will reduce the venom’s flow. However, holding the bite above your heart level will increase the venom’s flow.

• Remove all constricting items such as bracelets, watches, or rings before swelling occurs.
• Remember that using a cold compress on a venomous snake bite is not advisable. The cold may cause the local blood vessels to constrict and spread the venom faster.
• You can wash the affected area like any other wound with soap and water.
• You may cover the bite area with a moist dressing to reduce the swelling.

• Get medical attention as soon as possible. Call the hospital to tell them a venomous snake has bitten you. So they can have antivenom ready to give you when you arrive.
• A person whom a venomous snake has bitten may go into shock. If this happens, lay them flat and cover them with a blanket.

Dressing for Snake Country

• High-top leather boots and long pants are both wise ideas.
• Also, wear loose-fitting denim. If there’s a gap before the snake’s fangs touch your skin, your chances of being envenomated are lower.
• In the absence of high-top leather boots, some people wear snake gaiters.

Eastern Hognose Snake (Heterodon platirhinos)

Illinois is also home to the Eastern Hognose snake. Eastern Hognose snakes are one of three hognose snake species in the United States. They are rear-fanged colubrid snakes and are mildly venomous. However, outside of causing an allergic reaction, they are not dangerous to humans.

Here is a case of a Western Hognose snakebite.

The Eastern hognose snake, also known as the bastard rattlesnake or the blowing adder. They are smaller snakes with stout, short bodies. Adults average 28 inches (71 cm) in length. Their color is variable. They can be orange, brown, green, or gray. They can also be any combination of those colors. Their backs may be blotched, checkered, or solid-colored. The color of their bellies ranges from grey to cream.

These snakes derive their common name from an upturned nose scale. It gives their snout a long, hoglike appearance.

Eastern Hognose snakes live throughout the state of Illinois. Look for them in wooded areas, hillsides, farm fields, and river flood plains.

What Do Eastern Hognose Snakes Eat?

Eastern Hognose snakes feed on amphibians, rodents, and small birds. They are especially fond of toads. Some toads inflate their bodies, making it more difficult for snakes to swallow them. Eastern Hognose snakes get around this by puncturing the toad with their rear teeth.

Hognose Snake Behavior

When hognose snakes are threatened, they lift their heads and flatten their necks. This gives them a cobra-like appearance. They also hiss and strike without opening their mouths. They almost never bite. Instead, they headbutt whatever they’re striking at. If the hissing and false strikes don’t do the trick, they will roll over on their backs and play dead.

Garter Snakes

Garter snakes were long thought to be nonvenomous. However, in the early 2000s, scientists discovered that they are mildly venomous. Their saliva contains a mild neurotoxic venom.

Although they are venomous to their prey animals, they are harmless to humans. First, a garter snake’s mouth is too small, and their teeth are too short to break your skin. If a garter snake bite penetrates your skin, it might cause swelling and irritation. That’s the extent of the danger they pose.

Plains Garter Snake (Thamnophis radix)

Plains Garter Snakes have a greyish-green base color. They also have a yellow or orange dorsal stripe stretching from their head to their tail. They also have light-colored lip scales with dark separating bars. On average, adults grow 3 feet (91.44 cm) long.

These snakes are native to the central United States, from Texas north to Canada. In Illinois, Plains Garter Snakes live in the state’s northern half. Look for them in river valleys, sloughs, pastures, and meadows.

The plains garter snake feeds on a variety of prey. This includes amphibians, small fish, tadpoles, earthworms, leeches, rodents, and small birds.

Common Garter Snake (Thamnophis sirtalis)

Common Garter Snakes come in various colors. These include green, blue, yellow, gold, red, orange, brown, and black. Moreover, they grow to about 4 feet (122cm) long. However, most stay smaller than that. Most of them have vertical stripes that are yellow to brown over a darker background. They always have white scales on their upper lips that are separated by black bars. These snakes sometimes secrete a foul-smelling fluid from postanal glands when handled.

The Common Garter snake, or Red-sided Garter snake, is found across most of North America. They are the most common snake in Illinois, living throughout the state.

These snakes inhabit a diversity of habitats. These include forests, meadows, riparian zones, marshes, and vacant city lots.

Their choice of prey is similar to that of the Plains Garter snake. They feed on amphibians, small fish, rodents, earthworms, and insects.

Western Ribbon Snake (Thamnophis proximus)

Ribbon snakes are close relatives to Garter snakes. Ribbon snakes are slenderer than Garter snakes, though. Ribbon snakes also lack the black bars on their upper lips that Garter snakes have.

Western Ribbon snakes live in the western United States, Mexico, and Central America. Their range does extend into the midwestern states, though. Western Ribbon snakes live in the Illinois counties that border the Mississippi River. Their territory also extends further east into the state in southwestern Illinois.

Adult Western Ribbon snakes measure 17–50 inches (43–127 cm) long. They are olive-brown with three yellowish stripes. These stripes are located on the spine and each side of the snake. Their bellies are greenish or yellowish-white. The top of their head is dark green with a white spot in the center.

As with Garter snakes, the saliva of ribbon snakes is mildly venomous. They are not dangerous to humans, though.

Eastern Ribbon Snake (Thamnophis sauritus)

The Eastern Ribbon snake is a close relative of the garter snake. It is endemic to eastern North America. They are endemic to the southern tip of Illinois.

Adult Eastern Ribbon snakes measure 16 to 35 inches (41 to 89 cm) long. They are dark brown with three yellow stripes. These stripes are located on the spine and each side of the snake. Their bellies are greenish or yellowish-white. The top of their head is dark green with a white spot in the center. As stated above, Ribbon snakes lack the black markings on their upper lip that Garter snakes have.

Like Western Ribbon snakes, Eastern Ribbon snakes have mildly toxic saliva. However, they are not dangerous to humans.

Snake Road

Forest Road # 345 in Illinois’ Shawnee National Forest is world-famous. It is nicknamed the Snake Road. This is because the 2.5-mile road is closed to vehicles twice yearly to allow for snake migration.

The Forest Service closes the road from March 15 to May 15 to allow reptiles to migrate west into LaRue Swamp. The snakes have spent the winter denning in limestone cliffs east of the road. The road is closed again from September 1 to October 30. This allows the resident snakes to make their way from the swamp back to the cliffs.

Several species of non-venomous snakes make the biannual migration. You might also see Copperheads, Timber rattlesnakes, or Cottonmouths on the snake road.