Crayfish Escapism
Crayfish can easily swim to the top of a tank, then once up there hook on to the rim and crawl around until they find a way out. Mine also does climb the corners by using his smaller back claws to grab the soft silicone (there IS no excess, he just digs right in to it). They can also climb air hoses, heaters (which I know you probably don't have), filter tubes, ANYTHING.
Once they have escaped they are nearly impossible to find, and can travel quite a distance "on foot".
One of my friends has a turtle and he feeds it crayfish. When they are attempting to escape the turtle, they jet backwards with their tails. I have seen them do this so fast they jump clear out of the water and bang into the glass lid on top of the tank.
Fair thee warned!