Actually there are hundreds of species of crayfish, 21 in Ohio alone, and new species are still being described, even from Ohio! Some are very restricted in their habitats, limited to caves, or clear streams, or springs, and others are common and widespread. Two crayfish are invasive, if not in Ohio, then elsewhere.
The Red Swamp Crayfish (sometimes called the “Louisiana Crayfish”) is the one you may find in markets and as part of those delicious Cajun recipes. It is native to the southeastern USA but has been introduced to many other parts of the world, mostly for aquaculture. Where it is established it outcompetes native crayfish, impacts amphibian populations by feeding on their larvae, and its tunneling changes the pattern water flow in rice culture. Fortunately in Ohio the Red Swamp Crayfish occurs primarily near the sites of old fish hatcheries, although there is a large and expanding population in Sandusky Bay on Lake Erie. Freshwater biologists in states to our northwest, especially Wisconsin, are very concerned about the invasive potential of the Red Swamp Crayfish to harm native species, and are taking steps to limit its entry.
The Rusty Crayfish is Ohio’s most common and widespread species. It is native to central and western Ohio but fairly recently has spread to all areas of the state. Much of its movement is assisted by humans transporting live crayfish for fish bait. Its populations are expanding throughout the northeastern and Midwestern USA, and it threatens to overwhelm and replace some native species (such as the little-known Sloan’s Crayfish in Ohio). It feeds voraciously on algae, especially the common Cladophora, and in doing so it alters aquatic ecosystems, which is partly what defines “invasive.”
Like many invasive species, the Rusty Crayfish appears to thrive in waterways and ponds disturbed by human activities. A take-home message is that what may not be invasive in our own backyard might cause problems for someone else, and we must continue to be careful when we move living plants and animals around.