help with mantis

[g.t]

yesterday i seen a mantis shrimp on one of my rocks.he is about a 1" long and he is black.i had my rock now for about three weeks.i havent lost any crabs or snails yet.what kind can he be?
will he eventualy kill my live stock.i also have a clown & pygmy.

 

[mx250]

Just curious, where did you get the rock? I doubt it would hurt your fish, but crabs, snails, etc..., would likely be prime targets.