Originally Posted by jeffw85
I am wondering myself how big these little dudes have to be before they have the potential to start craking shells and such. Anyone have any idea?
Smaller smasher-type mantis will go after thinner-shelled snails and other smaller critters until they get bigger. However, they will continue to exercise their clubs on harder-shelled critters while they grow even if they are unsuccessful in breaking the shells.
Since you purchased your rock from Liverocks.com, you likely have a Neogonodactylus wennerae which are quite interesting. After a molt, they often change colors to be whatever color they think will be the most useful to them for camoflauge.
Assuming it is able to crack a hermit shell, I'm guessing that your mantis is now full grown. Wennerae tend to stay on the small side (2.5 to 3.5 inches).
PS...if you can trap it and put it in a nano tank, you'll be amazed at how fascinating these critters are.