I caught one at one of my local beaches a few years back. It never hurt a thing in my reef tank. It stayed at the bottom and just waited for me to feed it. It ate anything I would give it, shrimp, squid, silver-sides, anything. The thing I remember most about it is it was the fastest growing crab I've ever seen. I caught it when it was about an inch across. Around 5-6 months later it was pushing 5 inches across. The size difference after a molt was very shocking. He died right after his last molt, while his shell was still soft, a fish ripped him to shreds, I couldnt stop it... They were under the liverock.