MSU Extension Invasive Species

The Great Lakes Almanac to Invasive Crayfish pamphlet highlights four invaders: Rusty Crayfish (Faxonius rusticus), Red Swamp Crayfish (Procambarus clarkii), Marbled Crayfish (Procambarus virginalis), and Australian crayfish (Cherax species). For each crayfish species, a detailed description and illustration is provided highlighting significant physical features that can be used to identify the species.

Crayfish are important members of aquatic ecosystems and are a favorite snack for birds and other animals. They are also popular pets in aquariums. Unfortunately, well-meaning people who keep crayfish as pets sometimes release them into waterbodies, where they have the potential to become invasive and harmful to our environment. Of the ten crayfish found in Michigan waters, two are invasive: rusty crayfish and red swamp crayfish. Non-native crayfish such as the red swamp crayfish can rapidly reproduce, out competing our native species for food and habitat, and alter aquatic ecosystems.

Unfortunately crayfish identification can be very challenging. With over 600 crayfish species worldwide it can be hard to figure out if a crayfish in a fish tank or available online is a pesky invader. Retail crayfish are especially difficult to identify because they have been bred to have diverse colors, color patterns, and shapes. For this reason, physical features, not color alone, should be used to determine a species. Research has also shown that crayfish are not always sold at the wholesale or retail level with accurate labels, adding another layer of complexity. And when scientific names are provided on labels, they can also be inaccurate. Sometimes simple common names such as red crayfish, white crayfish, striped crayfish can be used to describe the same species.

Preventing the introduction of non-native crayfish is essential to the health of Michigan waterways. There are a wide variety of crayfish species in the pet industry and retailers, suppliers, and hobbyists are in a unique position to aid in the detection and prevention of invasive crayfish. It is imperative for retailers and hobbyists to know how to identify and report invasive crayfish.

If you have an unwanted crayfish, do not release it into Michigan waterways. Give or trade with a local retailer or other hobbyist.

Check out the Reduce Invasive Pet and Plant Escapes (RIPPLE) website to learn more and to order free copies of this poster. This product was funded in part by the Michigan Invasive Species Grant Program and the United States Environmental Protection Agency through the Great Lakes Restoration Initiative.

For the most up to date information about invasive crayfish and regulations in Michigan visit michigan.gov/invasives.