This is not like an emerald.

Red eye crabs are bad news. Remove. Remove. Remove.

Hairy crabs are generally 'bad'

Put a piece of people-food style shrimp in a glass and lean it up against the rock he's in
He'll be in the glass in the morning, or the next morning ( don't smell the shrimp when you pull it out :surprise: )

Take a pic for us and/or take him to the LFS for ID, or to be fed to something hungry :twised:

So I am curious to know why these crabs are so bad? Do they eat corals?

I had a hitch hiker crab in my tank... The glass trap didn't work so I got a syringe with a thick needle and skewered the little bastard. :what:

Opportunistic feeders. Could start taking snails out. Hermits. Eventually it might enjoy a fish for dinner. The one I had killed three.

My scary crab ate our sea hare
Grabbed it by the soft side from inside a hole when the hare slid by and pulled it in
The 4" hare was half eaten by a 1" crab before I found it

Ok, I guess the crab must go. You have me convinced!

Got one of this crab. Been eating my wallet.