They are not easy to catch by hand. Lift rock slowly and put your hand under it, scaring away the crawdads, etc. You feel for them then catch em like a crawfish. Some use a black net, lift the rock slowly and they head for darkness. I have seen guys catch dozens while I have only 1. There is not better smallie bait IMO.
I'll share a technique I learned many years ago while fishing the juniata.i wear an old belt with a hammer hook.carry a framing hammer with you.turn rocks until you find a stone cat, when he hides under another rock, hit it with the framing hammer.most times it stuns them and they float up when you lift the rock.sometimes it kills them, but dead ones catch.also other fisherman seem to steer clear of some nut whackin rocks in the river with a hammer, lol.i used to catch them at night when they are more active.
I looked into it and margined Madtoms, which is what we have around here, are legal to catch and use for bait. There is actually a species called stonecats, which occur in the ohio river basin, and are illegal to use as bait. I'm going to hopefully get out in the next week and try my luck. I'll report back with my results.