Hot crabs here, hot crabs!
When I first began fishing for bones I almost strictly used shrimp flies, so of course I caught all my fish on those. However, a small trip to Eleuthera a few years ago started me on crabs. We found this nice bay that held fish. It was sandy, wadeable and the fish were biggish. I was able to get 1 early on with a Gotcha, but after that we couldn't buy a hookup. On the way back to the car we noticed all these potholes in the flat, each one with a little, tan crab in the bottom. That night we whipped up a some #6 crabs and the next time we hit that flat... it was money. You'd toss the crab a little ways in front of the fish, wait till they got near, give one 6-inch strip and stop. You'd clearly see the fish dart forward, tip up and eat. Setting the hook was merely a matter of smoothly coming tight with an easy strip.
After that I started fishing crabs more at home and there are certain times when they really get the majority of strikes. This can be especially true with big, smart fish that will spook at the constant stripping action you mostly use with shrimp flies. That can also be the problem: crab flies are harder to fish than shrimp since bonefish mainly want the crabs sitting still so you have to watch for the strike. You can't feel it like you can if you're stripping a Gotcha or something.
Just this last winter season I did very well on crabs, so much so that they were my go-to flies. I tied so many #6 Merkins that I coudn't stand it. So, I simplified. I lost the rubber legs and splayed feathers. My crabs now consist of a tuft of marabou, three strands of yarn, mini-lead eyes and a weedguard. So simple it's stupid, but it works. It's all in the way you move it.