I got mine as a hitchiker about 6 to 8 months ago when I broked open a piece of liverock I bought with a SPS on it. There was a tunnel inside and this creature fell from the tunnel. It was the size of a large amphipods just a bit longer. At first I thought it was an amphipod and I was going to kill it (I hate amphipods) but then I saw the eyes and realized it was a mantis.
I put it in my quarantine tank and it went hiding in the rocks. I forgot about it and tought it was dead. Then I set up my new nano 15 gallons with a 10 gallons sump and there it was one day, flying through the tank at great speed. It's now 2" to 3" long and come to eat from the pipette. I will have to be carefull as he grab as much food as he can and go back in his cave.. I guess that can pollute if he does not eat all.
Mine is soooooo skittish, and rarely come out of its cave, only when I am feeding with the pipette. It took months for it to be tame enough to do this as before it was not even coming out for food.
When it was a baby it was light beige in color, but now it is starting to gain nice colors. Amazing how it grew from about 1/2" to 2" 1/2. I guess it must be pretty close to adult size.
I will try to post some video, if I can, because it is so skittish. I have it now with one large cleaner shrimp, 2 blue legged hermit crabs, 2 clownfish and a leopard wrasse (going in my 75 gallons soon).
I had it for months with an orchid dottyback and they lived well together, but since I sold the dottyback the mantis took the dottyback's cave and it's really happy about it.
man yer lucky i wish i could get a mantis as a hitch hiker u should try to figure out what type he is
heres a link to help if u wanna know