Hey Jim, if you haven't heard of them before they're probably not a problem. I think most of the states where they're a problem put advisories in their fishing bulletins. This site gives their range and pictures:
http://nas.er.usgs.gov/queries/SpFactSheet.asp?SpeciesID=214 Look for the big rusty spot on the side.
From what I understand, rusties will do the following:
- Consume all or most of the plants in a lake
- Outcompete other crayfish (for food and cover), causing them to die off
- Fight off fish to the point that fish can't really rely on them as a forage species.
In short, rusties have turned healthy lakes with normal fish populations into oxygen-depleted ones with little plant cover, few fish, and a whole lot of each other. On the upside, they're just as edible to people as other crayfish and grow bigger than lots of other species.
