Elementary my dear Watson...

DensityMan · #1 01/20/2004, 11:14 PM

So I get home from work2 and get to see the tanks lit for about 10 minutes before the lights click off/ I've been trying to locate a mantis from the 20lbs of new rock that went into the 75g tank to start the water stewing. Anyway, so I sit down in front of the tank and immediately notice something amiss...

There is a piece of LR missing from the rubble-pile:

Not only that, but there is a very clear (and relatively deep) trail leading away from the rubble pile...

more trail (it is a 48" tank after all)...

I finally spy the rock (alright... I saw the rock first, but it just doesn't make as great a story)!

If I were Sherlock Holmes, this fellow would be whatever ridiculous villain I were up against in this tale...

~~~
I know you probably can't ID him from the shot. I know the tank will be better off without him (and he will be moving into Tim's tank as a new roomie). What I really want to know (hence all the story telling) is how or why this crab, which is, as far as I can tell, not a shell-bearing hermit crab, drag/wear this cumbersome piece of LR rubble like an overcoat and walk accross the front of the tank??? Could this crab be the source of the mantis-like cracking noises?

Hoping this is at least worthy of a chuckle... couldn't think of a better place for it. If you can supply any partial facts on the crab and its seemingly odd behaviour that would be neat as well...

Enjoy!

rshimek · #2 01/21/2004, 10:13 AM

Hi,

Great story!

But....

Did you consider that perhaps the crab isn't your interior decorator? Both large polychaete worms and fish will move rocks like that (my tank gets regularly re-arranged by my Premnas female), and large eunicid worms have been photographed moving several pound rocks across an aquarium. Perhaps all the crab did was take advantage of a new hiding place.

Or perhaps, it moved the rock.

Some non-hermit crabs (generally in the crab group called the "Family Dromeidae" ) will carry quite large pieces of shells and rocks around. It is hard to tell from the illustrations, but it is possible that your crab is a member of one of that group. The way in which it is gripping the rock with its last pair of legs is rather characteristic of that group. I have some images of such crabs, but unfortunately none of them are scanned at the moment or I would add one to the thread.

You should do a short photo essay for of this (actually, you have already done this) and submit it to Skip Attix as a note for [rk]. It really is a neat occurence.

I don't know about the noises.

DensityMan · #3 01/21/2004, 10:25 AM

I thought the same thing, about it being anything else but that little crab... I have no fish yet in the tank. Only 20lbs of LR rubble in a 3 wk old 75g tank. Haven't observed any 'big' worms at night or during the daylight. I even asked my wife if she had been playing in the tank and dragged a piece of rock across the sand (you think it sounds silly here, I felt much sillier asking her).

After writing up that first bit last night I dimmed the lights and sat back from the tank so as to be less noticible. Very shortly there after the rock started moving as I watched. I crept closer and shined a light again on the rock to verify, but it was indeed the little crab just trudging along with an enormous (it's all in the perspective) piece of rock on its back.

This morning I found him and the rock halfway across the back of the tank (where I dropped a couple shrimp pellets before going off to bed).

Thanks for the info. I'll look into the "Family Dromeidae" and read up on their habits. I've already taken to calling it "Strongbad" and hope that he and the G. Smithii can work out a mutually agreed upon living arangement in the mantis tank.

DensityMan · #4 01/21/2004, 11:10 AM

"Family Dromeidae" indeed

I would know if I had an Emu living under and moving rock around in my tank.

At least I think I would.

After digging around Google a bit more and trying to limit searches down to crustaceans with that family name I have still had no luck. I am still having a good laugh and hope that last image helps other recognize when they may have an emu as a LR hitchhiker...

Thanks again!

rshimek · #5 01/21/2004, 11:49 AM

Hi,

You have WAY too much time on your hands.

I misspelled the family name, it is Dromiidae; you can find a lot of hits on them using google, but I didn't search through the hits looking for things of particular interset.

DensityMan · #6 01/21/2004, 11:58 AM

Many thanks Dr. Ron!

Reading on crabs instead of flightless, silly-looking birds now...

(The pic was just good practice.)

Forestal · #7 01/21/2004, 08:04 PM

Just want to say i enjoyed your story immensely

I look forward to hearing how he fares in the new tank

skippy2 · #8 01/21/2004, 08:27 PM

A great story. Now I will look for the emu at 3 in the morning.

DensityMan · #9 07/02/2004, 11:17 AM

Got rid of the emu shortly after that picture... he was too big to keep in there long-term. *wink*

Been meaning to do an update for a while on this little guy. I still have no idea what he eats specifically and have only noticed him molt once to date. He's still a pleasure to keep and Tim doesn't even pretend to notice him moving about...

He was given the name Strongbad shortly after indroduction into Tim's tank, though after just a couple seconds of thought now, it would've been better to call him Strongmad, Ben Grimm or the Thing in retrospect). *shrug*

I enticed him into a little photo-shoot to better show off his rugged good looks and his sole trick.

Home sweet (crabby) home...

*flip*

Better angle...

Getting a little brave...

Braver still...

Less brave... more creeping...

*pause*

*scamper* - notice the fine, smooth craftsmanship of his walls

*FLIP*

He really hates it when I do that, but I hate it when he bulldozes through the rock-work. It all balances out... *grin*

The photos above were all taken in the span of about 30 seconds and most of that was spent waiting for him to get the nerve to actually scamper out and flip his mobile-home over.

WetWilly · #10 07/03/2004, 09:34 AM

lol funny. If it matters, your posts made me laugh

rshimek · #11 07/03/2004, 12:25 PM

Hi Scott,

MANY THANKS!!!

chrali · #12 07/03/2004, 12:41 PM

That emu scared the heck out of me when i scrolled down! Wasn't expecting it. Very entertaining story.

FishGrrl · #13 10/25/2004, 05:52 AM

I just found this thread from the reef keeping article, and thought I should add my (belated) experience. I had a similar crab about two years ago. It started in a nano tank at work. I came into work one day, and thought my coworkers had been messing around with my tank. How else would a rock get moved? As I was fuming about it, I see the rock "jump" out of the corner of my eye. I was certain I was seeing things. However, careful monitoring the rock, i.e. staring at the tank rather than working, and I see it "jump" again. My first thought was some strange aquatic version of jumping beans.

Eventually I saw the culprit. He was much more orange than the one in the live rock pictured here. I had a great idea for him too. I took him home and placed him in my puffer/trigger tank. He turned out to be the only crustacean that survived with my puffers for any length of time. In fact, I think he would still be alive today, had it not been for a pencil urchin that ate apart his rock, exposing him to sharp, greedy mouths.

I always wanted another one, but its not exactly the type of thing you can special order.

sdm · #14 10/25/2004, 01:39 PM

Actually, if DM's ID (see his article) is correct, it is likely that google searching "sponge crab" or "sponge-back crab" you should find a number of places offering crabs of the family. Liveaquaria and saltwaterfish have Dromia spp. for sale.

FishGrrl · #15 10/25/2004, 09:14 PM

True, except I don't think your normal sponge crab drags around live rock, unless I'm misunderstanding this thread. And sponge isn't going to protect a crab from a puffer.

sdm · #16 10/25/2004, 09:30 PM

Aaaah, it's the same genus. "Sponge crab" is a far too generalized term-"sponge crabs" have been seen using: songes, rocks, shells, rubble, and any kinda junk they can find.

FishGrrl · #17 10/27/2004, 12:08 PM

Actually, same family (Dromiidae). Likely different genus (Hypoconcha). I'm fairly certain any sponge or decorator crab that is going to be available is not going to be the same as this critter. Even though they do decorate themselves with rocks, its rubble, not one whole rock, or in the case of the shell backs, one whole shell. Saying they're the same is akin to saying apes and humans are the same because they're from the same family Hominidae.

. . . but maybe I can just start asking shops to start keeping their eye on live rock that moves of its own volition. Then they can look at me like I'm really insane. "live rock, you know, doesn't mean it actually can get up and walk around." I can just see their reaction now.

sdm · #18 10/27/2004, 01:08 PM

nice catch! (genus? what was I thinkin?) But your thoughts have error. Spongeback crabs on saltwaterfish.com use a single, WHOLE object.

FishGrrl · #19 10/28/2004, 01:18 AM

Ohmygood. Thank you for pointing them out to me. I haven't seen them offered anywhere else before. Now I have to just wait for them to be available.