having been a former mantis-hater, i would now side with Untamed12 and probe you to try and look for other predators after lights out. I have 6 pistol shrimp in my tank which are getting more openly aggresive than I ever saw any of my mantis shrimp being. I also had a 3" long polyclad flatworm hitchhiker in my TBS tank. They are confirmed snail killers, but unless you spot it/them out and about, you'll never find them. they are like the Blob, and can ooze into just about any crevice. Good luck! if you truly want the mantis out, with the smart/stubborn ones, i always had to suck it up and pull their home rock out of the display and spray their holes with seltzer water to drive them out.