The foot, without the chitinous plate, is the chowdah part. Crabs are, for the industrious crab sheller, a real taste treat. Blues, and their less colorful lady cousins, are easily trapped with crab traps. Set your trap on channel and grass edges, in 1 to 10 feet of water. Put them out in the evening and check them first thing in the morning.
Big blues are mostly night hunters.
A better bait is a fish frame or a handful of clams. These are, after all, the usual foods of the crab. Shellfish will attract so many crabs, so quickly, as to be almost a nuisance. Sometimes you can come back in just 15 minutes to a full trap. Those claws are more like kitchen shears and will hurt you the same way, and in a blink of an eye.