They also are known to spear a fish on occassion. That long probosis isn't just for looks. They've been known to carry the carcass around on the end until they've finished eating it.
But, horrible rumors and the fact that like all crabs, they are insatiable opportunists aside, not everyone that keeps arrowcrabs has problems with them. It's a bit of a gamble whether yours would turn out to be a modle citizen-and then stay that way. If you have a large tank, you could probably overlook the ocassional depredations of a single little crab. Personally, I won't keep one in my little 55, no matter how cool they look.
