The invasive rusty crayfish probably arrived in Illinois waterways as fish bait

Jennifer Geer

When these aggressive feeders take over a river, they change the entire ecosystem of the waterway.
Rusty crawfish (Orconectes rusticus)(U.S. Fish and Wildlife Service)

Native to the Ohio River Basin (Ohio, Indiana, Kentucky, Tennessee,) Rusty crayfish (Orconectes rusticus) have made their way to the northern waters of Illinois, Wisconsin, and Michigan. Experts believe they were brought here by anglers that used them as bait and released the unused ones into the water.

Why are they a problem?

Usually, when we hear about a threatening invasive species, it's coming from a far-off continent, such as Asia. But these crayfish are only a state away. You wouldn't expect a species from Ohio to be able to cause much damage.

And yet, they are very damaging to the more northern rivers, streams, and lakes in Illinois.

For one thing, they are larger and more aggressive than the native species that make their home in Illinois rivers and streams. They can become quickly established in a body of water as the females lay 50 to 350 eggs in late spring.

The rusties then starve out the natives, causing them to die off or move to other locations. The changing ecosystem may eventually affect the population of popular game fish in an area.

The crayfish are also big feeders of bottom vegetation. They can wipe out aquatic plants, causing erosion of the sediment and the loss of nesting sites and shelter for small fish, insects, and other invertebrates.

Where have they been found?

The first rusty crayfish in Illinois was found in the Peoria River in 1973. Now the species has been discovered in 20 other states.

How can you spot a rusty crayfish?

Its green-brown to brown-red on its upper body. It has brown spots on its sides with smooth claws. They are larger than the native Illinois species of crayfish.
Rusty crayfish, found in the DuPage River, Morton Arboretum(Peterwchen/CC BY-SA 4.0/Wikimedia Commons)

What can be done to stop them?

Current Illinois laws prohibit the sale and possession of rusty crayfish. However, once the crayfish become established, it is hard to remove them. Chemicals used to kill them will harm the native crayfish of an area.

One way to help control the population is through their removal. Local conservation groups try to make the rounding up and disposing of them a fun family activity.

For three years in a row, in early August, the Forest Preserve District of Kane County, Hickory Knolls Discovery Center of the St. Charles Park District and Friends of the Fox, and the Red Oak Nature Center teamed up for an event where residents help remove the crayfish from the waterways.

What else can you do?

Never release a species of any crayfish into a different body of water than the one it came in.

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Jennifer covers lifestyle content and local news for the Chicago area. New articles published each weekday.

Chicago, IL

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