Snakes of Illinois
Learn about common snakes found around Northern Illinois homes, what they eat, where they shelter and how to respond when a snake appears indoors or near a structure.
Most Illinois snakes are harmless to people
Illinois supports many snake species in forests, grasslands, wetlands, yards and waterways. Snakes are solitary predators that help control insects, slugs, rodents and other small animals.
They have no eyelids or external ear openings and use their forked tongue to collect scent particles from the environment. Because markings can vary by age and individual, identification should consider the whole animal, its habitat and location—not a single feature.
Species homeowners may encounter
Common gartersnake
One of the most frequently encountered Illinois snakes. It often has lengthwise yellow stripes and may live in yards, gardens, field edges and near water. Its diet can include worms, insects, amphibians and small vertebrates.
DeKay’s brownsnake
A small, secretive brown or gray snake that hides beneath logs, stones, mulch and yard debris. It commonly eats slugs, snails and earthworms and is harmless to people.
Common watersnake
A heavy-bodied snake found around ponds, streams and wetlands. Its dark bands or blotches may become less distinct with age. Watersnakes are nonvenomous but may defend themselves when handled.
Eastern milksnake
A patterned snake with reddish-brown blotches bordered in dark pigment. Milksnakes may shelter around barns, foundations and rocky areas where mice and other small prey are available.
Gray ratsnake
A strong climber that feeds heavily on rodents and may explore buildings, trees and outbuildings. Juveniles are more distinctly patterned than many adults.
Foxsnake
A larger blotched snake associated with portions of northern Illinois. Foxsnakes feed on rodents and other small animals and may vibrate the tail when alarmed, but they are nonvenomous.
Why snakes use crawl spaces and areas beneath stoops
Protected voids offer darkness, stable temperatures and escape from predators. A snake may follow a foundation edge, enter through loose siding or use a gap that already allows mice and other prey into the structure.
Repeated sightings often point to suitable shelter, accessible entry points or a food source nearby.
Common shelter and access areas
- Crawl spaces and foundation openings
- Voids beneath concrete stoops
- Loose siding and corner channels
- Wood piles, dense vegetation and stored materials
- Areas with mouse, vole or insect activity
Four native Illinois species are venomous
The Illinois Department of Natural Resources identifies the eastern copperhead, northern cottonmouth, timber rattlesnake and eastern massasauga as the state’s venomous snake species. Their ranges and habitat needs are limited, and venomous-snake encounters are uncommon in much of Northern Illinois.
Do not rely only on head shape, pupil shape or color to decide whether an unknown snake is safe. Keep your distance and use a reliable species reference or qualified professional.
If you cannot identify the snake
Keep people and pets away. Do not touch, pin or corner it. If possible, observe from a safe distance and note where it goes. For a possible bite, seek emergency medical care.
What to do when you find a snake
- Give the snake space and an escape route
- Bring children and pets indoors
- Avoid grabbing or attempting to handle it
- Photograph only from a safe distance if identification is needed
- Note nearby gaps, crawl-space doors or shelter areas
Outdoors versus indoors
A snake passing through the yard may not require removal. A snake inside a living space, crawl space or repeated shelter location deserves closer inspection because it may reveal an entry point or prey problem.
Exclusion methods can include underground fencing, siding wrap, rodent proofing and other wildlife-resistant repairs matched to the structure.
Common questions about Illinois snakes
Why is a snake near my house?
The area may provide cover, warmth, moisture or prey. Nearby rodents, dense vegetation, debris and structural gaps can all contribute.
Do snakes eat mice?
Several larger Illinois species consume mice and other small mammals. Rodent activity can therefore increase the chance of snakes exploring a building.
Can snakes climb siding?
Some species are capable climbers and can use textured surfaces, corners and nearby objects. Loose siding and open channels should be evaluated during exclusion.
Will mothballs repel snakes?
Mothballs are pesticides intended for labeled uses and should not be scattered around a home or yard. Structural exclusion and attractant reduction are the practical long-term approach.
Explore professional snake removal and exclusion
See how we inspect crawl spaces and stoops, address the immediate animal and protect vulnerable areas with underground fencing, siding wrap and wildlife proofing.