If you know where it lives, u can pull out that rock and do a hyposaline dip. it will come out. u can also hang the rock over a bucket keeping it moist and it will come out looking for water and fall into the bucket.
LFS do sell mantis traps. be warned tho, mantis LEARN. do it right the first time. there are also DIY traps on this board. if u do a search, there are lots of ideas on how to build different types
also, there is a reason mantis are called thumbspltters, so be careful once you get it out...:yes: