If the tank has not cycled, then I would dip. Water will be toxic anyway through the cycle. The crabs are cool at first but they will get big and then start doing damage. Mantis are a nuisance really. I never saw it but heard it. I dipped my rock after it had been in my tank 4+ months and I got one off. I thought that was it but alas, I have heard clicking lately. The one I found was no where near as big as the ones in the above thread.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,