Stomatopod Log Entry: February 24,1998

Contributor: John Fordemwalt

Key ideas: effect of mantis on tank conditions; cohabitation of mantis & other tank inhabitants; effect of light on mantis shrimps; moulting (or non-moulting as the case may be) of mantis in aquaria.

I saw your snippet above and thought I'd send you just a few observations on the mantis I have in a small (25gal) reef tank. This tank is actually not doing as well as I would like (repeated algae outbreaks) in part because the mantis has been so effective in erradicating all the herbivors in the tank. At one point, the tank had over 35 snails (trochus(sp), nerite, and cerith) and 20 red legged mexican hermit crabs. This population has been cut to three hermits and a half dozen snails (the best that I can tell) over about a three month period.

As well, this little fella (perhaps 1.5" to 1.75" in length <ed. note: 4-5 cm>) shares the tank with a six line wrasse and a coral banded shrimp. I have noticed that the CBS is missing several legs, which I attribute to the mantis. I'm eventually expecting that the CBS will be a meal for the mantis.

This mantis is a fairly dark brown color (I've seen others that were a much lighter mustard color), with green highlights under the proper lighting. His favorite hole is approximately 1/4" <ed. note: approx 0.75 cm> in diameter and faces the front of the tank. Often in the morning, I can see his two little eyes surveying the surroundings from his hole. Of note is that he can clearly see movement outside the tank. When I come in the room, he completely disappears into his hole, but may emerge to the eyestalk if I stay still for a bit. If I move at all, he'll retreat again.

I have enticed him to come out of his hole with chunks of cut shrimp from the supermarket. He can really move! I will occasionally put a small chunk of shrimp in the tank for him (in a vain effort to keep him from preying on the snails and hermits). This does not seem to deter him from killing hermits and snails. (I'll also see hermits in cerith shells with the ends broken off - I can only assume the mantis did this either to get the snail or to entice a hermit to exit the shell.) He also will block the entrance to his hole with bits of shell, sand, and pulverized rock.

While I often see the molted skin from the CBS (usually partially sucked into the intake of a power head), I have never seen the shed skin from the mantis. I have had the mantis in this tank for over six months (came in with a live rock). However, with the state of algae in the tank, I may be forced to remove him. I think this is unfortunate because he is such an interesting creature, and he has chosen a hole which is readily visible from the front of the tank. (I often shine a handy flashlight into his hole if it is open. He *really* doesn't seem to like the light in his eyes - he'll curl up apparently into a ball and hide his face with his tail!) *

Oh, and one more anecdote: I was once cleaning the rock with the mantis' hole in it (the hole had been blocked off with shells and sand) and inadvertently knocked the hole open with a toothbrush. The mantis took poorly to having his hole invaded, and struck the toothbrush several times. Even at the end of the toothbrush, I could clearly feel the sharp snap. Good thing it was the toothbrush and not my finger!

Thanks for sharing information on these fascinating creatures on your web site!


Editor's note: Dr. Caldwell has informed me that eating of the molt skin is fairly common in the gonodactylids, and that is probably why the author of the log was not able to see one during this time. I have also noticed the curling reaction in some of the mantis shrimp that I keep, and I would guess that this reaction may be related to the common tactic of smashers to present their heavily-armored telsons to potential adversaries and threats.

Thanks to John Fordemwalt for the log entry.


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