Please visit our Sponsors

FAQs about Marine Crabs 3

Related Articles: Crabs, Hermit Crabs

Related FAQs: Marine Crabs 1, Marine Crabs 2Marine Crabs 4, By Species/Group:  Arrow CrabsEmerald Green Crabs, Decorator Crabs/Sponge Crabs, Fiddler Crabs, Pom Pom Crabs, Sally Lightfoots, & FAQs on: Marine Crab Identification, Marine Crab Selection, Marine Crab Compatibility, Marine Crab Systems, Marine Crab Feeding, Marine Crab Reproduction, Marine Crab Disease, Emerald Green, Mithrax/Mithraculus Crabs, Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone Eating ShrimpCrustacean Identification, Crustacean Selection, Crustacean Behavior, Crustacean Compatibility, Crustacean Systems, Crustacean Feeding, Crustacean Disease, Crustacean Reproduction,

Neopetrolisthes maculata in a Stichodactyla anemone.

Predatory Xanthid crab  3/5/03 Was wondering if you could ID this crab (small pic attached). I have three of them in my reef tank and I believe they are eating my fish.  Thanks for the help. <I cannot ID this crab by species with certainty but merely can say that it is a Xanthid species. Like most crabs, they are omnivorous with a strong inclination to be carnivores. I have no doubt that this creature would eat fish given the chance. Avoid most all crabs in reef aquaria and systems with small fishes. Kindly, Anthony>

Spider crab with a Decorating Fetish Date: Thu, 3 Feb 2005 Hello, thank you all for all you do. My Spider crab was banished from my 55 ga tank because he decided to mow down a colony of polyps and stick them on his ENTIRE body. Anyway he was transferred to my 15 gallon next to it.  When I was looking at my tanks the other day, I noticed my Long tentacle anemone moving. After looking a little harder I seen the spider crab "digging in" at the base of it. I left the house for an hour or so and when I came back, the spider crab had stuck the anemone on its body. The pink skunk clown was still swimming in its tentacles and the anemone crab was clinched to the base. The really unbelievable part is the crab is only the size of a hockey puck and the anemone is the size of a softball. I guess my question is, Ever heard of such a thing?  Corey  <Corey what I believe you have is what is called an anemone crab. These crabs will stick anemones to themselves which serve as protection for them. I think what you have is unique and I would leave it alone. James (Salty Dog)>

Crab Hitchhiker Crew: I have discovered what appears to be a Mithraculus crab in the Indonesian LR in my refugium. Should I be concerned about negative effects? Because of the layout of my system, any attempt to remove it will almost certainly kill it. Thanks, Steve Allen. <If it is truly a Mithrax crab no problem, esp. in a refugium.  Craig>

Re: unidentified crab sans QT 2/26/03 Thank you for your help...I know that quarantining for the rock is a necessary thing for the health of our tank...and we have been a bit lax in doing it lately (hanging head in shame.. G), as over a period of 2 years (and several QT periods) we have had no problems with live rock from this shop (our tank has thrived and grown tremendously)...however, that being said...that is no excuse for not being more careful... <all correct my friend> thank you for the reminder that just because we have not had problems so far...doesn't mean that we couldn't have problems in the future.     <I must admit that I learned my QT lesson the hard way too <G>> As far as the crab holding his claws in front of his face...we have seen no evidence of that.   <perhaps not Calappa then... rather conspicuous> He (or she) seems to keep them either tucked to the side or slightly out and down of the body.  I got a really great look at it's back last night (o.k. it was a 2 AM peek at the tank.. G) and it's back was not as smooth as we had thought...it's very slightly bumpy...and it's body is  squarish in shape as well.  I will send in a pic when I can get one (looks like another 2 am tank peek...LOL) and send it to you.    <indeed the best way for us to help ID for you> We did notice one thing that may or may not help...around where it was at...was a bunch of what appeared to be algae in little balls around it.  Also...I might not have been to clear. but it's  back legs are hairy. but it's pinchers are smooth....if that makes a difference.   <unfortunately not...  a couple hundred possibilities/species> Thank you for answering my e-mail...and I must agree with what a lot of people have wrote about you guys. you are awesome!!! <thanks kindly! It really is a labor of love> Thanks again!  Will start re-searching the shame faced crab today. Lee
<best regards, Anthony>

Crab ID Must of came on live rock any ideas? <Mmm, no... e pluribus unum! Bob Fenner>

Starfish and crab questions - 02/21/03 <Ananda here today...> I have a quick and easy (guessing) question this time.  What does a sand-sifting starfish eat?  I read on your website most starfish eat mollusks or shrimp once or twice a week but thought this sand-sifter may be different because of #1, its name, #2 because it is so small (probably 2.5 inches from top to bottom).   <Sand-sifting stars are called such because that's how they get their food: they sift through your sand bed looking for goodies to eat.> I have a 55 gallon FOWLR that has several different fish, snails, and two cleaner shrimp.  I fed the fish frozen foods such as Formula one, two, brine shrimp plus, plankton, and krill.  The only problem is the fish obviously eat all the food before it could settle for the starfish to crawl over it.  Should I, and if so what, feed the starfish individually? <The best way to keep these critters fed is to have a good sand bed full of the stuff they normally eat. A critter-producing refugium can help supplement this.> I also have a closing question.  I saw an emerald crab in the LFS with no claws, just two legs on one side and four legs on the other side.  Will it grow claws in time or not?  Will it be able to eat without claws or will it die? <When it molts, it should regenerate the claws and legs. Whether it will live to do so is another matter. This crab uses its claws to bring food to its mouth -- so unless it molts very soon, it may be out of luck.> As always, thanks. Ray <You're welcome. --Ananda>

Calappa Shame-faced Crab?  - 2/25/03 Hello! I have been looking all over the internet trying to find a picture of the crab I just discovered in my reef tank. When I ran across your web site, I just had to ask if you could possibly identify the crab.   <please send a picture later for a better ID> The story behind this unexpected critter,  is that about 2 weeks ago we bought some live rock for our 30 gal reef tank.  Two days later, <Yikes... 2 days later indicates a lack of quarantine for this rock. Beyond the risk of importing a parasite, pest or disease, QT is necessary for all live rock to verify stability. A stress to the rock or large invertebrate mass inside (Holothuroid, Echinoid, etc) could wipe out your entire display tank. Please be sure to QT every single thing you buy in a separate tank for 4 weeks prior to entry into your display tank. Else it is a matter of time before something really bad happens. Please browse this site and beyond for articles and information about QT protocol> I discovered that one of our blue legged hermit crabs had been smashed to pieces.  All that was left was a smashed up shell and maybe 2 legs.  I thought at first that maybe some of our live rock might have fallen and  smashed the crab, then my husband (or another family member) re-stacked the rock. I questioned everyone, but no one seemed to know anything about it.  I thought that maybe some one wasn't telling me the truth, and I didn't give it much thought after that.  Then today I was doing a weekly  water change, and cleaning up the tank, when my eye happened to see some really quick movement in the tank.  Since we do not have any fish, or anything that moves really fast, I was thinking that maybe my eyes were playing tricks on me.  Just to be sure, I started watching the tank.   After watching for about 5 minutes, much to my surprise, I seen this crab come creeping out of a hole!    <crabs are very common with live rock... all are opportunistic predators... most are dangerous indeed. One of the many reasons for a proper QT period. in Qt they are easily trapped by propping rock off the bare glass bottom of the tank and baiting the floor with meaty food. All the crabs come out for dinner <G>> It is dark grey (or black) in color, it has no outer shell (at least none that we could see...due to possibly molting?)) and it's back is smooth, light grey and black (or dark grey) and checked (kind of like a checker board), it has 2 light grey streaks running vertically between it's eyes.  The eyes are not on stalks and are red in color.  It's legs are really squat and thick and square-ish in shape and hairy looking.   <big and hairy claws are the giveaway that it is predatory> It is also about 1 to 1 1/2 inches wide at most.  It is the most bizarre looking crab I have ever seen...and I cannot seem to find a photo of it anywhere.   <its hard for us to ID this crab without knowing the geographic origin of the rock and w/o a picture. Still... I would ask if the claws fold tightly in front of the crabs face at times (like a shield)? Wondering if it is a Calappa species. Calappa are highly variable in color and form... but most all fold their large thick claws in front of their face> We went back to the place where we bought the live rock, and they had no clue as to what it was and suggested that it could be a baby emerald crab.  I have seen tons of pictures on adult emerald crabs, and no pictures on baby emerald crabs, but I don't think  this critter is a baby emerald crab (or an adult emerald crab either...but hey, I could be wrong).   <Mithraculus is indeed doubtful> I am hoping that you can help me to identify this critter.   <do send picture and research Calappa forms in the meantime across the 'Net> I have pretty much figured that this unknown crab ate the blue legged hermit crab, <agreed> but I have never heard of a crab ripping the shell to pieces.   <actually... it is extremely common among crabs. Some can rip apart snails including conch shells!> Am I wrong to think that the crab did this??? <agreed> Thank you for your help with this critter! Sincerely, Lee Brisboy <best regards, Anthony>

Crab Id please? Hey Crew.. I think I've found the clicking source from my tank. <nope... but I'm glad to hear your optimism :) You still will hear the clicking. Quite likely a small pistol shrimp from the live rock or sand> Think this is it? <Nope> Some kind of crab? <yep... this image shows a Mithraculus (AKA Mithrax or Emerald Green crab). They are good algae grazers but dubiously reef safe in the long run> Thank you!
<best regards, Anthony>

Re: any idea what this crab is? Hello,   I caught this guy in my reef tank after he was pushing around a coral.  He has also eaten two small clams.  I won't go into details about him eating the clams, unless you would like me to. His shell is about 1.5". <Nice photo. Don't know the species, but it's likely a member of the family Xanthidae. Please see here: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm and the linked FAQs (in blue, at top) beyond. I would remove this crab. Bob Fenner> thanks in advance,
Keith MacNeil

Re: any idea what this crab is? Bob,   Thank you for your response.  I did remove him and put him in a specimen cup with a lid and holes in my grow out tank.  Now I just have to figure out what to do with him. thanks again, Keith <Maybe your local fish store will take "him" in... and find a home that's suited. Bob Fenner>

Re: crab in my clam There's a small white crab living in my small Tridacna maxima clam.  I thought I might have read something somewhere in which these were described as potentially commensal, but now my searches don't turn anything up.  Knop only seems to write about crabs doing bad things to clams.   <yes... more of what I have read about incidental shrimps and crabs in the gills suggests they are mildly to very harmful> I have had these clams for about 4 months, and when they first arrived, I found the crab in the attached photo on the outside of another clam and removed it. The clam is looking stressed.  The mantle is not fully extended, but otherwise looks ok. Should I make an effort to remove this crab? <I would indeed... you can make a brief magnesium salt bath (same SG as sodium seawater). If necessary... a brief FW dip can be used to force the crab out. Many clams are intertidal and will tolerate the FW just fine> Thanks! Michael <best regards, Anthony>

Crab Dear sir,             About 1 year ago I noticed a small crab in my reef tank which I just caught a glimpse of and no more, I thought nothing else about it until I spotted it recently.     It's body is about 2.5 cm.s long and is reddish in colour with hairy legs and it's claws had black tips at the ends. I looked up a few pages on the internet and thought that it might be a red rock crab. I haven't lost any livestock up to now but if it is a red rock crab does it pose a danger to my tank and what size will it grow to, also, if it has to come out have you any suggestions on how to do so?                                yours sincerely                                                                Mr. J Robertson <Mmm, from the description of the claws, size I suspect you have a Xanthid crab (please see here: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm), and further from your notes I suspect it is of no dire consequence to your livestock. Most members of this family of decapods reach a maximum of two inches (5 cm.) across. Bob Fenner>

- Mystery Crab - Hello WWM <Hello, JasonC here...> I yesterday I emailed you guys about a crab that I had found as a stowaway on some live rock I recently purchased. <I do recall.> I just wanted to send you some pics of him so you can maybe help me identify him. <Well, it's safe to say that is a crab.> Cuz I have no clue what he is. <And neither do I.> Maybe you can help me. Thank you for your time. Matt
<Cheers, J -- >

- Hairy Crabs - Hello again WWM crew. <And hello to you, JasonC here...> Last night I decided to bait out the little cave critter with some krill tied with some clean fishing line. Found out it wasn't a Mantis shrimp (whew there). What I did find was a really hairy crab. I looked on the FAQ for crabs and saw someone else write about a crab he couldn't identify that looked like a tarantula. That's exactly what this guy looks like. He's got a grayish body with some hints of purplish red and he's got purplish red arms and legs. Later on after doing more research trying to find out what it might be called I came across pictures of the Mithrax Sculptus aka Emerald Crab. This guy looks Exactly like one of those only minus the Green color. <They do come in other colors.> Same build and everything just no green and he's got a bit more hair on his body. <Sometimes the crabs put that there to disguise themselves.> If you guys could help me identify this crab I wouldn't mind keeping him in a small nano reef based around him if he doesn't get to big. <Sounds like you've done about as well I as I could do identifying this crab. You have the advantage of seeing it with your eyes, I can only read descriptions, which generally aren't enough.> Ill be baiting him completely out tonight using the Nylon stocking trick and a good net. So Ill have my Digi cam ready to take some pics and possibly send so you guys can get a better view of what he looks like. <That would help.> Thanks for your time and efforts :) Matt <Cheers, J -- >

Re: Blue Eyed Crab What can you tell me about Blue Eyed Crab.  Do you have any information <I have lots of information, but none on a "blue eyed crab" - do you know this beast by any other name? Cheers, J -- >

All You Can Eat Crabs? Dear WWM crew, <Scott F. here tonight> Please can you help me with my hermit crab problem. Since Christmas I have lost 1 small red crab, and 2 blue crabs. They seem to have died in their shells, and only the red crab had legs missing. Before this the largest blue crab had died, he was whole, but away from his shell. My livestock is: 1 yellow tang, 1 six line wrasse, 1 fireball angel, 2 clowns, 1 blue cheek goby, 1 scooter blenny. I have a few blue crabs left and a zebra hermit, who is very quiet at the moment, any suggestions why? I also have a pom-pom crab, that I got in October. My readings are all good. <Sounds to me like someone is having a little buffet there! Hard to say if it is the other crabs, the wrasse, or even the clowns...I've seen this kind of "warfare" before; usually it turns out to be some kind of fish that is the culprit, but it's tough to say. I would have suspected a possible iodine deficiency or something if it weren't for the "parts of the crabs" that were missing...I say predator. Keep a close eye on things, and I'm sure that you'll find your answer.> Thanks in advance, James Matthams <Your welcome, James- just keep on observing! regards, Scott F>

Shame faced crab <Hi Chris, Ananda here tonight.> Hi. I've been reading through much of your site recently and it has already answered so many of my questions. <Good to know.> I do have one that I have not been able to answer via your site or the rest of the web though. I have an established 10g nano reef with about 10lb of LR. I picked up a hitchhiker which looks to me like a shame faced crab less than an inch in length. <There are two photos of the shame-faced crab here: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm ...does yours look like these guys?> The intentional inhabitants currently residing in my tank are a small yellow tailed blue damsel, one percula a fire shrimp and a peppermint shrimp (along with some red hermits and snails). I am wondering whether I need to get the crab out of the LR or not. <If you've followed the link and found the photo, you've seen the note: "not to be trusted with invertebrates". I would remove it. It is a cool-looking critter, so perhaps you could find it a home in an invert-free refugium, if you have one. If not, consider putting it into your quarantine tank (or some other container if necessary) for the short term until you can find a home for it.> He's been in there for about 3 days and has not done any noticeable damage yet. <Perhaps. But with a beautiful and expensive fire shrimp, I would remove this critter post-haste.> You opinions would be greatly appreciated. Thanks for your attention. Sincerely, Chris <You are quite welcome...we are here to help. --Ananda>

Re: shame faced crab Thank you for your response Ananda. <You're welcome.> I'm trying to get a pic of him to no avail as of yet since he only comes out at night and runs when I whip out the flashlight. <Have you tried using a red filter over the lens? Additionally, your crab's being nocturnal is another indicator that it may indeed be a shame-faced crab.> From what I do see, he often expands these large fan-like appendages from the front of his mouth. They are large in comparison to his whole body. I see him chowing down on some of the small tufts of hair algae right before he runs for cover. Do all crabs extend these large appendages as mine does? <I have not seen this in the crabs I have had.> Coloration wise, he looks similar to the shame faced crab pic on the right. He is very small though (less than an inch in diameter) <All crabs start out small....> The fire shrimp is pretty big around 2.5" from head to tail. Removal of the crab is in progress <Ah, good.> and hopefully I'll have a pic to send for a real identification. <Looking forward to it.> Thank you again. Chris <Happy to help. --Ananda>

Popeye and The Crab From Another World? Hi there again Mr. Fenner, <Scott F. here today> I recently emailed you about a clownfish with a case of Popeye.  Upon receiving it, the whole thing was somehow butchered.  I wish to apologize for the annoying inconvenience. <Never a problem> I believe the reason for the whole mishap was because of our new internet service.  Anyway, to the point.  It seems my oldest (and favorite) fish, an Amphiprion ocellaris, has somehow managed to contract Popeye.  It is a mature female in a 75 gallon reef aquarium. It has a mate and a host sea anemone (Heteractis crispa).  It is housed with numerous invertebrates including shrimp, hermits, LPS and SPS corals, as well as several other fish tankmates.  These include a Sixline wrasse, yellow tang, a blue tang,  and a reef safe yellow wrasse (pet store said it was a yellow Coris wrasse and I know it is not).  Those are all the fish.  Believe it or not, I recently lost my yellow tang at the same time my poor clownfish contracted the disease.  With the simultaneous occurrences, I suspected water quality as the culprit.  But, on the other hand, the corals looked excellent.  I decided to run full water tests anyway. <Good procedure!> When all was said and done, the parameters were all in the green, if not optimum.  They were as follows:  Ammonia 0, Nitrite 0, Nitrate 0, pH 8.3, Ca 450, Alkalinity 3.5 mEq/l, S.G. 1.025, Temperature 80 degrees.  With seeing the results, I was stumped as to what actually caused my yellow tang's untimely death.  I was beginning to think of the clownfish and its eye as a fluke accompanied by some misfortune.  Since the clownfish does have a disease, how can I go about treating it.  I want do cause as little stress as possible, preferably without removing the fish from the tank.  Are there any treatments that I can perform or should I leave her to her own devices and heal? <Unfortunately, if you are going to intervene with medication, you need to remove the afflicted fish to another tank for the treatment. If the disease is indeed Popeye, and not just an injury (if an injury, you can use Epsom salt to reduce swelling), you should treat with an antibiotic, such as Maracyn 2> And now back to the tang.  I have figured two possibilities:  1) fish was spooked and jumped out, then my dog summarily ate him (the canopy lid was raised to lower temp) or 2) there is a small (relatively speaking) stone crab present as a hitchhiker that has eluded my grasp in all instances (including when I broke the tank down to find him).  Could it have been this demon that ate my tang? <Possible...hard to be sure> I already know I must find a way to remove him (then I can sell him to my local pet store for a quick buck).  All considered, could you help me to find out what to do? <I'd opt for removal, if you suspect this guy to be the culprit!> Please help me with my clownfish as it is a favorite as well as a best friend .I suppose it is a little too late for the tang:( Thanks in advance, Andrew <If the Popeye is in one eye only- it's probably due to injury, and Epsom salt/good water quality/time will do the trick. If its both eyes, you need to use medication, IMO. There is a lot more on this illness in the wetwebmedia.com archives. You can use the Google search feature and look under 'Popeye". You can save this fish with quick action! Good luck! Regards, Scott F.>

Unknown Crab Hello, <Hi there> I wonder if you could help. We've found a small (approx. an inch across), very light green, almost translucent crab, in the invertebrate tank today. It's probably been there for about a year and we haven't noticed any major problems, although we do keep seeing marks on the pair of clown fish in the tank. <Probably caused by each other> Do you think it will be a problem? We also have a fish set up with gobies, yellow tang, blenny etc. where it could be transferred. <Mmm, I would shy on the liberal live and let live side here. Unless you see actual destructive activity by this crab, I'd let it be, enjoy it. Bob Fenner> Many thanks, Maureen

Clams, Anemones and Crabs Anthony I can keep the crocea and maxima species in the top 10" of my tank.  I might have to rearrange some of my rockwork, but that's alright.  I'm going to check out the sample chapter in just a moment.  I'm sure it will be excellent reading. I thought emeralds were ok with clams.  Hmm.  Might move it to the 34gal as well then.   <there are no crabs that are wholly reef safe... all are scavengers. Some favor algae but none to exclusion. Mithraculus (Mithrax) emerald crabs literally grow large enough to eat after a few years. They can pull down 4" fish at that time. So if something is weak or sleepy enough... its fair game. I personally enjoy many crab species and fine them interesting. I would almost never put them in a reef tank > I'll leave it in until I acquire clams though, as it'll help with the algae (small bloom, probably due to the every other day feeding of zooplankton to the anemones...  switching to small cuts of silversides soaked in Selcon so that should help with the nutrient pollution as will the further stocking of my refugium). <exactly my friend... the problem isn't a lack of crabs, we just need better control of nutrients. You can continue to feed heavy too (I almost prefer it)... just be more aggressive with skimming, water flow and water changes (weekly carbon changes too)> They have been easy enough to catch for me. After re-measuring the depth of my sand bed it's around 1"-1 1/4" deep.  I had read from many sources that a sandbed deeper than 3" on a tank my size is next to worthless.   <I would disagree... and I have some experience here. I imported 48,000 pounds of sand for my greenhouse and coral farm. Used it in every way imaginable for the last decade. Pictures of it in my Book of Coral Propagation. I'm not saying I'm right.. just that I have a valid contention> I suppose I could pull out more sand without any issues though, <agreed> and remove the starfish to the other tank as well since this will be lacking the depth for it to be comfortable. Yes I noticed in some of my physics classes the effect of lighting through the atmosphere and the surface of water. <huge> I've actually been able to lower them down to about 1" off the surface.  That brings up a good question..  I have an overflow on my skimmer.  It helps with the surface gunk but there is still more there than I would like.  Any ideas? <I'm not sure what the question is specifically> Smack me all you want!  muahah I slap back!  I was thinking of the rest of my livestock in case the bleached anemone were to die.   <how about putting it in your waiting quarantine tank then and resisting the purchase of a new organism until the anemone recovers, dies or a second QT tank is purchased. A 20 gallon tank in a South or East facing window would be very fine for anemones> Better to let it go alone than to take my entire tank.  hehe  But I definitely see your point, and will keep it.  It will be a good test of my husbandry skills - to nurse it back to health.   <agreed <G>> Did not mean to seem hypocritical with the statement about flushing it. <no worries... I know that you really meant that you would find another aquarist in your area to carry the torch for it anyway. No destroying right?> That said, I just ran out of test kits and since I needed a better quality test setup I just ordered a full Salifert test kit.  Tests some 9 parameters of my water.  I should be able to keep a closer eye on water quality with that one.  Not to mention more accurate. Err I'm getting married soon!  Don't scare me! Hmm scratching is good! Any aquascaping suggestions for an anemone/clam tank?  Never really seen or heard of one.  Right now I have kind of an island like this -------------------------------------------------------------- | | |              oo oo oo o   o o o          o o oo  o oo    | |           ooooooooooooooo       oooooooooo     | |              ooooooooooooo     o o o oo ooooo    | | | -------------------------------------------------------------- that is the top view.   <you really have way to much time to spend on the computer<G>> Probably a side view would be more important considering clam placement.   <do a keyword search on Reefcentral.com for "Japanese reef aquariums"... some excellent and artistic examples> There aren't really any flat areas that a clam would likely be comfortable on.  I can put the Squamosas and derasas in the substrate ok, <agreed... but still with a flat rock buried underneath them in the sand to protect against predation> but any Croceas and Maximas will be hard to place I believe. Hrmm.  Aquascaping isn't my forte...  yet.  Give me more practice!  I can be very artsy ya know.  hehe Wow I'm full of questions.   <I would certainly agree that you are full of it> I really hope I am not bothering you.   <heehee... no worries. We are here to answer and abuse you with pleasure> Just so you know your time is not in vain, as I am learning more and more every day, especially through such e-mail correspondence! RVM <very good to hear... do pass your wisdom along in kind. Best regards, Anthony>

- The not-so-Emerald Crab - <Greetings, JasonC here...> I went to my LFS tonight and found an Emerald Crab that was pink instead of green. I of course had to purchase him but am really curious as to why he's this different color. Is it common for these to vary this drastically or did I get an oddball? <Well... my guess would be that this is not an actual emerald crab [Mithrax sculptus] but perhaps a close relative - there are other crabs in the Mithrax family which have the coloring you describe. Another option is the crab's diet, which can also affect the coloration. Perhaps we should ask the crab... ;-) > My LFS said they originally thought it was because he was going to shed but they have had him for close to 2 weeks now and nothing has happened so they believe it's just his coloring. He is eating *very* well and shows no signs of disease. <Ahh good.> On another topic, when a Turbo Grazer Snail is bred, how long until they lay the eggs? <Oh... that is a good question, and one to which I don't have a very good answer. My guess is about a week perhaps less, depending on temperature.> Ronni <Cheers, J -- >

Not a minute-man! (Emerald Crab) Hello, oh helpful ones: <whassup, bubba?> So the other day, I see my Emerald Crab isn't moving. I figure, okay, I'll wait a day and see if he moves.  Nothing.  So, I finally take the poor guy out and say goodbye.   <literally or figuratively on the "goodbye" part?> Then, I figure, while I have the gloves on, I'll move some of my LR around a little.  Lo, and behold, my Crab moves from under a rock.  A few questions, numerically, if I may: <rock on my brother...> 1.  I guess he molted (this is a first for me)? <indeed... a molt of the exoskeleton. Conspicuous in some lazy arthropods that leave it lying around... rare with others that eat it promptly (for Chiton/protein recycling)> 2. Now I read that you're supposed to leave the molt in the tank.  Is that true? <true for above reasons> 3. I already got rid of it.  Is that bad? <no biggie> 4. Is 2 weeks considered fast? <fast?!?! 15 minutes is pretty good for most of us... 2 weeks (!), you are a god. Your poor wife/girlfriend.> 5. What would influence the speed of a molt? <diet, water changes and iodine for some/many> As always, thanks for all your help.  Rich <no... thank you for giving our team a good name <G>. Best regards, Anthony>

Killer (Xanthid) Crab Good morning Crew, Can you please try to I.D. this white little monster that's making a meal of my blue starfish. I never see him during the daytime, but last night, I placed a few silversides in a nylon stocking & set it next to his hole. Within minutes, he pulled the bait into his hole. I ended up playing tug of war w/him & was able to retrieve the bait. Any ideas on how to catch him. I think he has been killing/eating my smaller fish (Firefish, Bluespotted jaw & small chalk bass). Thanks in advance for your time Craig <This is a Xanthid (Black-Finger Crab, family Xanthidae) of some species... and it should be removed, post haste. I would bait or trap this predator out. Insight on how to do this is posted in a few places on our root web: www.WetWebMedia.com. Please either use the Google Search tool there (on homepage or indices) or go to the Marine Crabs FAQs sections. Bob Fenner>

Ocypode spp.. Ghost Crabs Dear sir, Are Ghost Crabs of the genus Ocypode also suitable for a freshwater-Amazon and beach aquarium? <Good question. I ran a search on the family and the Amazon, Brazil... no one mentioned the use, physiological plasticity of these Crabs and total freshwater... they of course do make the transition between terrestrial and marine to brackish habitats.> I have had so far about 14 different species of crabs alive in this tank over the past years. All of them did very well and seemed healthy. But I am planning to make the tank suitable for Ocypode-crabs, but I am not quite sure if the can survive in a freshwater tank. I suppose they could, since they are semi-land crabs. Do you have any information about this? And if so, is it possible to get ghost crabs from certain aquarium shops? <I have occasionally seen the ocypodids collected, sold in the ornamental trade. You might ask your local/national import dealers re species availability. Bob Fenner> Thank you and regards,   Steven Campbell

Crab ID and trapping I just got an id on a crab that hitchhiked on my LR from Tampa Bay SW, Gorilla Crab.  I can't find anything on this site, virtually nothing on the web.   <that's because somebody made up that common name, bud... and there are no popular references to it commonly.> Do any of you know the scientific name of this brute?   <you'll need to send us a photo, my friend. Something more than a common name> I know he's a bad guy and I want to get him out of my main tank, <exactly> but I'm having a hell of a time catching him. Thanks, Mike <try leaning a small glass jar (like for pickles) in the aquarium against the rockwork with weighted meaty bait in the bottom. The crab will scurry down into the jar for the food at night but to be able to scurry back up the slick glass. Best regards, Anthony>

Harlequin shrimp/Emerald crab question Greetings, JasonC here. I've not actually heard that Emerald crabs can be a threat to Harlequin Shrimp directly. That being said, there aren't many crabs that can be trusted much farther than you can throw them. They're quite often too opportunistic for their own good, and the well being of other tank inhabitants. I do know from my own Hymenocera that they will use their flat paddle-like forelegs to wave about and chase off the too-curious. I would just keep an eye on the crabs. Good luck, J --

Crab ID Hi guys, I have an ID problem with a true crab. I'd love to send you a picture but I can't. This guy is about 3/4" across the carapace, very hairy/bristly, coloration seems to be purple and white especially on his legs, banded in these colors. He is a hitchhiker on my FL Keys LR. I have several other crabs, all much smaller (half that size for the biggest) which appear to be of the "Sally Lightfoot" variety, although I'm not convinced that this ID is accurate either. Anyway, as for the big hairy guy, his claws are disproportionate with the left being dominant. His claws look just like the Stone Crab claws, which you may have eaten. (I may grow this crab to maturity just to harvest a claw. :) I plan to eventually have a couple of seahorses in this tank. Is he (he IS a he) safe for my horses (4"-5") or should I remove him to my refugium to fight it out with the Mantis Shrimp (also a hitchhiker) that lives there? <I would remove.> BTW, all have of my crabs have molted since I've had them, 2 months. I'm assuming that's a good thing. <It means they are growing.> Any idea on the ID? <No, but better to be safe than sorry.> Sorry, I know it's vague. All these crabs seem to be algae eaters; but I know that all crabs are opportunists. <Yes, very opportunistic and seahorses are slow and would be easy prey.> Thanks, Mike <You are welcome. -Steven Pro>

Lazy Snails I have a 20gal FOWLR which had a green algae problem. I took out the rock and scrubbed it and did a 25% water change. Now my snails or hermits do not move and they fall off the rock. I know they are alive because they do react when I touch them. What do you think the problem is? Should I pull them? All the water parameters are normal. I also have a problem with keeping a sally light foot crab for more than a couple of months. Shaun Nelson <Hi Shawn, Thanks for writing. Your algae comes from excess nutrient, either as a by product of fish and feeding, or in the source or replacement water. Scrubbing the rock does nothing to resolve this excess nutrient and in fact retards the ability of the rock to help process these wastes. Go to WetWebMedia.com and look up "live rock" and also "algae". You don't mention any water parameters other than to say they are "normal". The nutrient for algae is coming from somewhere. Test for ammonia, nitrite (should be zero for these) Nitrate, phosphates, silicates. Don't forget to test the source water. My guess is the snails, sally lightfoot, etc. are reacting to wastes, likely nitrates. They are also sensitive to salinity changes so make sure you aerate, match SG, heat, buffer, test any new water. The idea is to maintain a stable system low in nutrient for algae. Craig>

Cleaner shrimp and crab not surviving in my tank Hi Craig, <Hi Jun!> It's me again. I purchased a cleaner shrimp and a sally light foot crab today (third or fourth cleaner shrimp and the second light foot crab in the last 6 weeks). Within several hours they're already dead. What am I doing wrong? Water parameters are all good. I followed the acclimation process and still no luck. Please help!!!!!!! Thanks.....Jun <Hmm, did you purchase these from a local fish store or have them shipped? If shipped, this could be from adding a normal pH water to a waste laden shipping bag, perhaps affecting the toxic ammonia levels.  Also, these guys are incredibly sensitive to salinity changes. If there is a big difference in salinity it needs to changed very, very slowly, like over a day or so. A drip line works well for this and changes water very slowly. These guys are sensitive! I sure hope this helps you. Craig> 

Crab identification Greetings Bob, A follow up to a previous email you answered regarding a stowaway on a piece of LR I recently purchased: here are 3 of the best pics I could get...he is a shy one. The next pic shows the yellow tips and "hairy" legs, claws are the same left and right neither is larger than the other). you can get a decent idea of them from the picture above. a correction to my last email, the tank has been up for 2 months but the crab arrived with a 29lbs chunk of LR 2 weeks ago. As far as I can tell he only seems to be eating detritus from the sand, but I haven't been able to observe him with the lights off. Any help in identification would be greatly appreciated! <the crab cannot be identified by species but the photo clearly depicts this specimens large crushing and hooked claws (in contrast to small pinching/algae cropping claws). As they say... "Form Follows Function". This crab is clearly an omnivore leaning toward predator with the hooked claws. It may behave for 10 days or 10 months... but rest assured that it will attack something desirable in time in the confines of an aquarium. Do remove (to sump, QT, refugium, or elsewhere)> one more thing, in the first picture you can see a discoloration on the anal fin of the Flame Angel. It is actually a clear spot on the fin about 1.5mm in size...almost completely transparent. The Angel has been in the tank 2 weeks, with 2 weeks in a Q tank before that and seems very happy. Any clue to what this may be? <no clue from the photo but does not yet sound pathogenic. Feed well and observe for changes> Thank you very much, Emerson <best regards, Anthony>

Emerald Crab Greetings Bob and Crew!<<Greetings to you too!>> I just recently bought two small emerald crabs to take care of some algae in my tank. I know that they will grow larger and attack my snails and fish, but I'm hoping not for a while. When they do grow too large, I was thinking about buying a Marbled Cat Shark. I have a 100 gallon and in Scott W. Michael's Sharks and Rays (Bible) said that the Marbled cat shark can be housed in a 70 gallon aquarium. Do you think the shark will be able to take down the two crabs? And if not, how would I go about taking them out? I am not so worried because they are both less than half an inch wide, but still, I want to plan for the future. Could you tell me a good way of getting rid of them? Thanks Bob I really appreciate it!. Thanks and I love the site! <<Catch them and trade them in at your LFS. I would not recommend keeping a marbled cat shark in a 100. Yeah, maybe a 70 for less than a year. Sharks get BIG, are messy, require massive filtration and skimming, streamlined/angled corners, no powerheads or stuff to knock loose, etc. Please read the shark info at http://www.wetwebmedia.com/sharkfaq.htm  Many letters regarding your interest. Many requirements you are unaware of to learn about here! Please look carefully before you leap! They require BIG systems. Craig>> 

Mithrax Bob, please stop me but I have more questions. I just found this website today. ;) I was wondering on your thoughts regarding Mithrax crabs? Specifically I've seen (and caused) some debate on the boards recently as to whether these crabs are bad guys are not. Many people swear they were caught red handed feeding on corals. But many others have argued that maybe they were just cleaning damaged tissue. I challenged people to speak up if their crab was not only caught picking at the coral but that the coral showed tissue damage. No one really seemed to have any hard evidence that they had caused any real damage. But I saw on the website that these are known fish killers. I'd like to hear your thoughts on the issue. Cheers, Chris (aka newkie) < Hey Chris, Gage here. The problem with crabs Mithrax included is that they are opportunistic omnivores. They will eat anything that they feel like eating fish, coral, snails, other crabs. If they think they can take'em they will have a go. Check out this link for some more info on Mithrax and other crabs. http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabfaqs2.htm>

Crab question Please forgive me if I ask about something already in a FAQ...I've been reading them for about hours and haven't found info pertaining to my crab in question... <Mmm... no worries re asking... A note re a possible tool here, the Google Search feature on the Homepage and Indices... might be of service if you can formulate the search terms to match "closely" what's archived on WWM> at least not specific enough to warrant killing a free crab. <Indeed... some are very useful (in keeping down numbers of other "pest" organisms, cleaning up... let alone beautiful, interesting...)> After purchasing a 29lbs piece of live rock at the LFS (I noticed something scurry up inside the rock as the salesman strained to lift the piece out of the tank...excited to what I may find when I got home) it turns out I have acquired a 1" dark maroon crab with very "hairy" legs and hairless claws which are relatively long but not wide. The best info I have found so far leads me to "bristle crabs" which supposedly don't fair well with inverts which I plan on keeping after upgrading lights and adding another 20-30lbs of live rock. <Okay> My question is: should I make an effort to remove the crab now? The tank is 3 months old with 2 damsels, a flame angel, snails and hermits, 65lbs of live rock in a 55g with Emperor 400 and Red Sea Berlin HOT...dinky power compact at the moment but will be going with a 200w 36" pc system soon for the planned Sebae anemone and coralline algae. <A "maybe" answer... it's been a few months, the crab isn't "too big"... and doesn't seem to be "eating too much"... I am inclined to take a "wait, enjoy, and see" keep your eye on it point of view> I've had no luck determining what this crab is, please help is you can. <Many possibilities here... the only species we have to show you for comparison are posted here: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm If you can supply a photo we can pass it about, ask others re...> Thanks! btw: after spending a couple years keeping Malawi Cichlids a friend of mine with a reef tank loaned me the "bible"...The Conscientious Marine Aquarist of course! Needless to say I was sold. What a surprise to find a website run by Mr. Fenner. <Mmm, not so surprising... for one, there are a few folks who make these sites a reality, on the other, what better tool than the Net to share ones thoughts, attitudes, factual material, images, methods...? You would, will do, have done the same> One more thing: should I run more biological filtration other than the Emp 400 and live rock? <I wouldn't... until which time you're ready to add a sump/refugium as an adjunct to what you have.> total bio load will be 2 damsels, flame angel, Pearlscale butterfly, 2 Perculas with a Sebae anemone, maybe a goby. After the tank cycled it stays around 5ppm of nitrates with weekly 7g changes in its current config. Is there anything I should worry about after adding 20 more lbs of live rock and the butterfly etc? <... just that the rock is relatively "cured" to start with... Bob Fenner> Crab question (same crab, different responder) Please forgive me if I ask about something already in a FAQ...I've been reading them for about hours and haven't found info pertaining to my crab in question <They are quite vast>...at least not specific enough to warrant killing a free crab. <or returning to the fish store?> After purchasing a 29lbs piece of live rock at the LFS (I noticed something scurry up inside the rock as the salesman strained to lift the piece out of the tank...excited to what I may find when I got home) it turns out I have acquired a 1" dark maroon crab with very "hairy" legs and hairless claws which are relatively long but not wide. The best info I have found so far leads me to "bristle crabs" which supposedly don't fair well with inverts which I plan on keeping after upgrading lights and adding another 20-30lbs of live rock. My question is: should I make an effort to remove the crab now? The tank is 3 months old with 2 damsels, a flame angel, snails and hermits, 65lbs of live rock in a 55g with Emperor 400 and Red Sea Berlin HOT...dinky power compact at the moment but will be going with a 200w 36" pc system soon for the planned Sebae anemone and coralline algae. I've had no luck determining what this crab is, please help is you can. Thanks! <Without a picture of the crab it is hard to say what type he is. It would be easier to remove him now before you get everything situated. There is some good info on catching crabs at the link below. http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabfaqs2.htm btw: after spending a couple years keeping Malawi Cichlids a friend of mine with a reef tank loaned me the "bible"...The Conscientious Marine Aquarist of course! Needless to say I was sold. What a surprise to find a website run by Mr. Fenner. <I accidentally spilled a 5 gal bucket of water on my copy, it is a little more weathered now, but still good reading.> One more thing: should I run more biological filtration other than the Emp 400 and live rock? total bio load will be 2 damsels, flame angel, Pearlscale butterfly, 2 Perculas with a Sebae anemone, maybe a goby. After the tank cycled it stays around 5ppm of nitrates with weekly 7g changes in its current config. Is there anything I should worry about after adding 20 more lbs of live rock and the butterfly etc?  <I would add the live rock, wait a few weeks, and check the water quality frequently. You want your nitrates down around 0. Once the tank gets going the LR will be able to handle the bio load, no need to add any other bio media. Once the water is stable then I would quarantine first, then add new fish to your display tank. Good luck, Gage>

Crab identification Hi there! <Howdy!> Just when I thought it was safe to start adding new live rock to my tank another crab showed up last night. UGG! Just the body is 1", there are eight legs and two claws (of course claws *chuckles*). Anyway, I just walked in to look at the tank and there it was. ACK! Okay, break down half the tank and now have it quarantined. <very wise> My original base rock (that's been such a pain) is from an eco-conscious place in Florida with a lease 1-2 miles off shore. (All my other hitchhikers came from this rock, which is why I assume Florida.) I was wondering if you could suggest some good links for identifying Florida crabs or might have some idea what this crab is.  <yep... Humann and DeLoach "Reef Creatures"> I've been searching the net since last evening but am not having any luck in finding the type of aquarium crab links I need. <in terms of "reef safe"... no research is necessary: no crabs are long-term safe in reef aquaria. With only rare exceptions, most all are opportunistic scavengers... even "safe" crabs like Mithrax have been observed killing fishes, "reef" hermits killing snails, etc. I'm not one for absolute rules... but "No Crabs" is close to being valid> The crab seems to be more of a mottled dark brown than black, on a white background. Its body is oval shaped, smooth and the legs are very compact to the body. I've attached some pictures that I hope will help. <quite frankly... the pictured crab does not look especially threatening to me. Large smooth carapace, small claws, etc... indicates a likely nice guy to me. Still... now that its out of the tank... leave him out. Perhaps remit it to a refugium or sump. You can also tempt it with meaty foods to see how much of a carnivore it is and offered algae at the same time. Best regards, Anthony> Any help much appreciated!! I actually don't mind the way this crab looks, but after past hitchhiker crab experiences in my reef call me a bit paranoid. :-) CJ

Re: Crab Question thank you for your help. I'm curious as to whether this might have to with the reproductive process of certain types of crabs. Of I still have no picture but maybe my description was not to clear. The belly of the crab seems to open laterally and what look gills on the underside of a mushroom seem to occupy the space in the body. thanks AGAIN. <indeed... many crab species carry eggs in a "trap door" on the abdomen. Best regards>

Become a Sponsor Features:
Daily FAQs FW Daily FAQs SW Pix of the Day FW Pix of the Day New On WWM
Helpful Links Hobbyist Forum Calendars Admin Index Cover Images
Featured Sponsors: