The rusty crayfish (Orconectes rusticus) is native to the Ohio River basin in the United States. It has been distributed to other areas around the country, most likely as unused bait released by fishermen. It arrived in Wisconsin in the 1960’s and has since established itself as a nasty invader throughout the upper Midwest and can also be found in New England and some western states (full map here).
A jump from Ohio to Wisconsin may not sound like a big deal. People do it all the time. However, the rusty crayfish occupies streams in its native Ohio range and behaves quite differently when it settles into lakes. Rusty crayfish can reach much higher densities than resident crayfish species because they out-compete other crayfish for shelter and food and are more aggressive with predatory fish, which makes them less likely to be eaten. Rusty crayfish are capable of altering the character of a lake when they reach high densities; they clear-cut aquatic plants, consume large numbers of snails and aquatic insect larva, and even impact the fish community.
Invasive Crayfish: It’s all Relative
I have an affinity for the virile crayfish (Orconectes virilis), perhaps because we are both natives of the upper Midwest. In my reference frame, the virile crayfish are the modest native species that are constantly bullied by the feisty rusty crayfish. My values were challenged when I discovered that virile crayfish is a scorned invader in Europe and several US states.
This story highlights the diversity of crayfish and how a species can be benign, even threatened, in its home range while being TOO successful in another. There are over 500 species of crayfish worldwide, 75% of which come from North America. Many of these species have very specialized and limited ranges. Some species, such as the rusty and Louisiana crayfishes, are able to do very well in an expanded range, while other species are more vulnerable to changes to their familiar conditions. On a final note, it strikes me as ironic that the primary threat to native crayfish diversity is the introduction of new crayfish.
The silver lining here is that many different invasive crayfish make tasty treats for invasivores. Tomorrow, I’ll be sharing two variations on a crayfish boil recipe that are sure to impress.
This species profile comes to you courtesy of guest contributor Ashley Baldridge. Ashley is a PhD student at the University of Notre Dame whose research focuses on the impacts of invasive rusty crayfish in Wisconsin and Michigan.