Mantis Explosion

[yawny]

About 2 weeks after bringing in a piece of rock with corals from the LFS, I started noticing signs of burrowing activity in the biggest rock in the tank. Then I started seeing little crustaceans running in and out of the burrow holes, and a few dead (transparent) crustaceans bouncing around in the water column every day.

At first I assumed these were amphipods as most of them were so small, and even the bigger ones (3-5 mm) had a striped or banded appearance... and they seemed to lack the telltale folded appendages and eye stalks seen in the mature mantis.

However now that this brood is growing up it's clear that some or all are stomatopods. Last night I saw two clear examples, dark red, 5-7mm each, coming out of each of two main burrows.

I set traps but so far nothing. In the last few weeks I've lost a couple of snails but these could easily have been crab victims, as at least one blueleg is sporting a new Nerite snail shell.

So my questions are:
(1) while these mantises are still juveniles, will they cannibalize each other? Right now there are literally scores of the little fellas running around at night, god knows how many inside the rock. I'm wondering if they start exercising their own population control while their numbers are still legion.
(2) how fast do they grow? assuming the biggest is 7 mm (say 1/4-3/8"), and that they are smasher types, how soon might they start presenting a danger to the inverts in the tank?

Basically I want to know how much longer I can wait and watch, and when I need to start taking action. I'd like to keep one or two in a spare 6gal eclipse nano tank that I have but right now they're pretty hard to catch.

 

[AttackDonut]

Yes, they'll happily chow on each other, but bear in mind they chow on everything else to boot.

Probably take some months do whittle them down to manageable levels, and even then that's too long.

If they are all hiding in that one rock, perhaps take it out and put elsewhere?

 

[yawny]

Yeah unfortunately it's the centerpiece of my 37 gal, it's a 20-pound rock with all kinds of coralline, feather dusters, a huge spaghetti worm, brittle stars, a soft coral attached, etc. etc.

Not only would I have to tear the whole tank down, but doing the club soda or freshwater routine would kill a lot of good stuff.

I may try squirting club soda into the burrow holes, then trying to net any that come out, but even in the best case I figure this is unlikely to make a big dent in the overall population.

That's why I was hoping to count on the little devils to help manage thier own numbers.

 

[DensityMan]

Re: Mantis Explosion

Any chance you have some photos or are able to take and post some?

Everything you've mentioned so far gives me the impression they are not mantids but could instead be isopods or even larger amphipods.

I do not know the odds of them cannabilizing themselves as I bet that would largely depend on hunger and species. Most will fight over territory or burrows. I have read of cannibilization after mating in some cases...

Yes, they'll happily chow on each other, but bear in mind they chow on everything else to boot.

Man is this stereotype true. Just last week the police came to my door twice. The first time looking for the mailman (accident, he got to close to the tank) and then again for my mother (I told her not to stand so close to the tank)... I was worried the police may find some clue or piece of vital evidence linking my mantis to the crimes, but I needn't have worried. He ate all the evidence, then the desk his tank rested on and then consumed himself from the tail up. After he finished that last meal I thought my other tanks would be safe for certain, but sure enough fish still disappeared and sometimes corals died. I knew it was still that damn mantis though. They kill everything!

(The above paragraph is a work of sarcastic fiction. Tim was in no way harmed during the writing of said piece. The mailman will turn up someday and I still haven't been able to get the maternal-unit close enough to the tank to interest him...)

All mocking aside...

Smashers are fairly commonly imported as hitchhikers on liverrock. They do eat/hunt/kill gastropods of various species/type and perhaps various crustaceans as well; shrimps, crabs or hermits. During faminous conditions they may experiment with other foods as well or may accept other prepared foods as well.

Spearers are less common in aquaria, especially so from LR as they typically build burrows in the sand/mud. Spearers do hunt/eat/kill fish. They are not specialized to eat gastropods or hard-shelled crustaceans.

These are generalizations I've learned here from Dr. Roy and elsewhere on the BlueBoards and from various books.

 

[yawny]

Unfortunately my camera sucks for closeups. I'll be getting a real camera soon. Here is the best I could do, last night. It's very blurry...

But there are two crustacean-y critters in this shot: if you can see the pink coralline patch right in the center of the image, the one I have ID'd as almost definitely a mantis is below and to the right of that patch--looks like dark red coralline. It's come almost all the way out of its burrow and is foraging around on the rock surface.

I've included a second, equally bad photo so you can compare and see how the red guy moved in the picture.

There is also a clear-colored guy just to the left and a little above the pink coralline.

I just captured a baby specimen (about 5 mm) and looked at it under a microscope. It definitely appears to have the smasher appendages but it's so small it's hard to tell. He's still alive so I put him in a jar with a tiny bit of food.

Some mantis-like behavioral notes: in the photo, the clear-colored guy is standing up straight. Do amphipods do this? All of these guys are extremely flexible and roll about in the burrow holes. And lastly, they like to park themselves in the burrow with just the tip of the carapace and/or the antennae protruding, then rush out to get little bits of bait that go by the burrow hole.

This is probably typical of other types of crustaceans too, but seem to be common characteristics of stomatopods. Oh yeah, and the occasional tank clicking sound. I have that too esp. around 8-11 pm.

 

[yawny]

OK, I just pulled out a cantelope-sized rock and did the club soda trick. I got about 15-20 small critters. And this is not even the main rock.

I quickly put them in a 6 gal nano tank with some aquarium water in it and a few rocks. Some of them are still alive, though stunned. I got a good look at one of the bigger ones, there is no question this is a smasher guy. He has triceps like Popeye.

 

[Cube Crazy]

Would you like to send one my way if they get bigger? I will pay for shipping. let me know

Thanks,
Dave

 

[traveller7]

Please take offers and discussions to PM or the sale/trade forums.

Thanks

 

[dwarfatize]

You still have yet to convince me that they are mantis shrimp. Mantis shrimp have yet to breed and be raised in home aquaria. I know some scirntisis have raised them but those were under extremely controlled conditions.

Do they look like this?

 

[Gonodactylus]

I can't tell from the photos if these are stomatopods, but if I make out a pair of eyes correctly, they probably are.

It is not uncommon to have a massive recruitment of postlarvae in the field. If those rocks were then harvested and shipped fairly soon, you could have dozens of juveniles in a rock. I don't remember ever seeing this in the trade, but I have certainly collected rubble in the field that was full of juveniles.

As for eating one another, not likely. Cannibalism is a problem when trying to rear larvae, but not juveniles. The comment was made that stomatopods have not been reared in the home aquarium. That is true if you mean egg to egg. It is relatively easy to rear postlarvae to adult if you have enough time. In Neogonodactylus wennerae, egg to egg is close to two years and the total life span is five or six years.

These animals are NOT going to be a major problem to any tank mates larger than they are. They will eat micro-crustaceans, amphipod juveniles, etc.

As for how fast they will grow, that partly depends on food. However, I can tell you in the field that postlarvae (usually 6-9 mm) molt twice a month and grow around 10% a molt. As they get older, the rate of growth slows considerably. After 6 months, they will be 15 - 17 mm and after a year around 22 - 25 mm Breeding starts around 25 - 30 mm.

Roy

 

[yawny]

Ah, so the little transparent crustacean shapes bobbing around the water column every day are probably molts and not entire dead organisms...? That would make sense -- whether they're amphipods or stomatopods or both.

I'll see how the juveniles do in the nano tank. I'm not too optimistic but right now it looks like about 5 or 6 of them survived the club soda ordeal.

As for the microscopic view, the eyes in the one I looked at did not seem as developed as in the picture above, but they might have been damaged from all the moving around and getting squished on the slide. However the raptorial appendages were gigantic, and looked exactly like every picture I've ever seen of a juvenile mantis.

I'll post more pics if/when I get them. My son has a junior microscope, I'll see if I can get a photo of a specimen...

Thanks Roy and everyone else who responded.

 

[Hwarang]

Please take offers and discussions to PM or the sale/trade forums.

Spammer.

 

[traveller7]

Spammer.

I think you meant to say enforcer ;>)