i have always thought of emeralds as to slow to get a mantis. my little smithii has a technique though. first he circles the emerald, the emerald cant keep up and bam! he hits it!. circles again and bam1 bits it in the same spot, what he does is takes the merald claws of and eats them, by then the emeald is hhiding in a corner with no protection. it looks so wierd though, a 2.5 inch smithii draging a crab that is a bit bigger than it. he never seems to get it into his home though.