Today’s featured Michigan invasive species is one that I am intimately familiar with since I used them for my graduate school thesis experiments, which I’ll tell you all about another time. This species is the rusty crayfish, and the State of Michigan is serious about controlling their population, for reasons you will learn below.
Name: Orconectes rusticus, commonly called the rusty crayfish.
Native Range: Ohio River Basin including Ohio, Kentucky and Indiana.
Description: The rusty crayfish is a small, lobster-like crustacean up to 6 inches in length. Their most distinguishing feature is the rusty red circle on both sides of their carapace (the part of the body just behind the head, ending at the segmented abdomen). They also have dark bands at the tips of their large front claws, and their claws have gaps when “closed”. They usually also have a wide, rusty red stripe down the back of their abdomen.
Habitat: Rusty crayfish are very hardy, but generally prefer well oxygenated waters 68-77 degrees Fahrenheit and clay, silt, cobble, or gravel substrates. They are rarely found in waters deeper than one meter, except in Lake Michigan.
Negative ecological impacts: This little critter is the perfect storm of negative ecological impacts. They have about twice the metabolic rate of native crayfish which makes them voracious eaters. They are also omnivorous and will eat just about anything they can find, including macrophytes (large plants), algae, macroinvertebrates, fish eggs, small fish, detritus (dead stuff), snails, and clams. Juvenile rusty crayfish also grow faster than native juvenile crayfish, which makes them better competitors for food. Their large, indiscriminate appetites destroy delicate plant beds that are used for nesting and as shelter for juvenile fish and macroinvertebrates. Their constant cutting of plants increases the spread of invasive Eurasian water milfoil, which spreads by fragmentation, while reducing populations of native aquatic plants. Their relatively dense populations compete with native crayfish species as well as juvenile fish for food resources, meaning native crayfish are often crowded out and fish survivorship to adulthood is decreased. They also increase fish predation on smaller native crayfish by ousting them from their burrows, leaving them vulnerable. Meanwhile, adult rusty crayfish assume a claws-up defensive stance (see below) near fish rather than swimming away, which leaves them less vulnerable (they are ballsy little suckers).
Positive attributes if any: Rusty crayfish are good bait for fishing, which is likely how they were introduced into Michigan waters in the first place. It is illegal to use them as bait in any Michigan waters. Rusty crayfish are supposedly good to eat (I haven’t tried personally). It is illegal to catch and move live rusty crayfish EXCEPT for the purposes of cooking and eating them. Catch as many as you like and have yourself a good old-fashioned crayfish boil while helping stream ecosystems!
Key identifying characteristics:
- Rusty red dot on both sides of the carapace
- Rusty red stripe down the middle of the abdomen
- Claws with dark bands on the tips that have gaps when closed
How to report this species properly:
To report his species, use this link for the Midwest Invasive Species Information Network. They’ll ask you to register (one time only) before you can report your sighting, but the good news is that once you’re registered, you’re all set to report again next time you find an invasive species! You can also learn more about invasive species using fact sheets on this site or browse their data which is pretty cool.
More Info:
State of Michigan’s Management Plan for rusty crayfish
Invasive Species Profile from Michigan.gov
USDA National Agricultural Library Species Profile, which links you to many federal, state, local, professional, and academic resources and task forces.