Please visit our Sponsors
FAQs on Freshwater, Terrestrial Crab Behavior

Related Articles: Fresh to Brackish CrabsFreshwater CrustaceansInvertebrates for Freshwater Aquariums by Neale Monks, Forget Crawfish Pie, Let's Make a Crawfish Tank! By Gage Harford

Related FAQs:  Freshwater Crabs 1, Freshwater Crabs 2, &FAQs on: FW Crab Identification, FW Crab Compatibility, FW Crab Selection, FW Crab Systems, FW Crab Feeding, FW Crab Disease, FW Crab Reproduction, & Fresh to Brackish Water Crabs, FW Crustaceans 1FW Crustaceans 2, Terrestrial Hermit Crabs, &Marine: Hermit ID, Hermit Behavior, Hermit Compatibility, Hermit Selection, Hermit Systems, Hermit Feeding, Hermit Reproduction, Hermit Disease/Health, & Crayfish FAQs, Crayfish 2, Crayfish ID, Crayfish Behavior, Crayfish Compatibility, Crayfish Selection, Crayfish Systems, Crayfish Feeding, Crayfish Disease, Crayfish Reproduction,


Re: Mr. Crabby – 8/29/13
Anyway, no new crabby news from me right now.  Mr. Crabby is still waving his big claw around to no one in particular and doing his crabby man dance all over the tank.  The girls are paying no mind to him.  The tank is due for another cleaning - Yay!  They will be happy but I am not looking forward to the four hours it takes....At least I have it down to a pattern now of what to do.  Most likely I'll give them some krill this afternoon before I clean their tank this evening.  I usually like to give them some good stinky food for a nice feeding before I clean......
My friend with the hermit crab is figuring things out regarding sand....lol. He said it got too wet and started stinking, which I told him it would!  He had to buy new sand and he bought some other type of bedding/substrate.  He also has a crawling wall along the back and apparently they like to crawl up it and up to the screen top.  They also got an additional hermit crab and within a day of being brought home from the pet store, he changed shells....haha.  I know I asked you about iodine for them - where should they add it or how should they give it to the hermit crabs?
<Add to the bathing water.>
It's easy with the Fiddlers to add it to the tank water, but I wasn't sure how to tell them to give it to their hermit crabs...especially since the bottle says to give such a small amount/gallon.  I know they have a salt water dish (they buy the bottled salt water) and a fresh water dish....but is that too small of an amount of water to put the iodine?   
<Possibly; if it's easiest you could mix with tap water in a large empty soda bottle (a couple litres here in England) and then store and use as required. Somewhere cool and dark, but need not be refrigerated. You can then decant as much as you need.>
Thanks for your advice for me and for my friend now too!!!  I know he said he appreciates it because he didn't realize what a learning curve there was for hermit crabs!!!  He also said he was shocked to find out they could live for 15 years or more.....haha.  I thought that was funny.  I keep laughing at him because it all started with his little girl wanting to win a crab at the carnival.  As you mentioned, we used to have carnivals with goldfish and when I was little we won a little goldfish.  Of course that turned into us buying two more goldfish as friends for him....and it turned into a ten gallon tank and them living for over ten years!!!  So, I know how that goes with a carnival "win" turning into a costly long-term investment. 
<Ah, yes, a common "problem" with animal visitors. On the other hand, the rewards of animal ownership are many, especially for families with children -- patience, responsibility, passing of time and resulting growth, death, birth of next generation... so much easier to explain these things to children when they can experience it through their animals.>
Well, I am sure you'll be hearing from me again as I know I'll have questions.  For now, I think I am good.....lol.
<Real good! Have fun with the various animals in your care, Neale.>

Red Claw Crab Missing Limbs   10/12/10
I purchased 2 Red Claw Crabs from PetSmart.
<Perisesarma bidens and interesting, if aggressive, brackish water crab.>
I believe one was male and one was female, do to the markings on their underbellies, plus one had slim claws, and the other had fat, wide claws.
<Do bear in mind males and females view each other as food except when mating!>
After about a month, one crab (female) molted. She was seemingly fine after the molt, with all appendages in tact. Two days later, 2 legs and both front claws were missing. I removed the other crab (male), assuming he attacked her. Three days later, the attacked crab died.
<As often happens.>
Am I correct in assuming the other crab attacked her?
<Possibly. When crabs moult they would normally hide in places such as caves or bury themselves in leaf litter. Either way they'd be out of view. Crabs view one another as potential meals, and in their "soft" state they're easy targets. A lot depends on their environment, and in a spacious tank with plenty of hiding places crabs can moult successfully. But if you crab two crabs in 5 or 10 gallon tank, it's hard for them to avoid each other, and if there aren't any good hiding places, and I mean REALLY good hiding places, not some upturned flowerpot, then they can, will attack one another.>
Did the molt have anything to do with what happened here?
<Can certainly be a factor. But bear in mind lack of iodine is a very common reason for failed moulting. Use marine aquarium iodine supplement at 50% the quoted dose per gallon of water. Also make sure their diet is calcium-rich -- a mix of whole lancefish, unshelled shrimp, and suitable soft fruits should do the trick, along with regular offerings of crustaceans foods such as those from JBL, Sera, and others.>
Would the lost appendages result in her death?
<Not in themselves, no, but lack of iodine can cause various problems, deformed appendages merely being the most obvious symptom.>
Also, I've read on your site that RCC are land crabs, but mine stayed in the water most of the time.
<Well, they are land animals. In the wild they live in estuaries, dipping into brackish or salt water periodically but foraging on land. On the other hand, for a variety of reasons they may prefer to stay underwater in a given aquarium, perhaps because there's only enough dry land for one dominant individual. Cold and dry air can also stress them.>
My tank set-up: 10 gallon tank, part land, part water. Sea salt mixture added to water,
<How much? You really need brackish water, not "teaspoon per gallon" amounts of salt. Use marine aquarium salt at not less than 6 grammes per litre (~3.8 US gallons), and ideally 9 grammes/litre, for a specific gravity of at least 1.003 and ideally 1.005 or more at 25 C.>
with calcium and other trace elements especially for invertebrates.
<Iodine is the key, and yes, you do need iodine supplement.>
Utilized a terrarium filter to clean the water. Fed spirulina flakes, bloodworms, krill, and crab pellets. No heater was used in the water.
<Well, that's one problem. They are tropical animals. The air needs to warm and moist. Essentially you're creating a habitat similar to what you would for tree frogs, except the bathing pool contains brackish rather than fresh water. Apart from that, the coconut fibre substrate will be similar, and the bogwood and plastic climbing branches will be similar.>
After this experience, I do not believe PetSmart should be selling these crabs.
<Difficult to argue against. But they are bizarre animals, and some dedicated individuals have even bred them! The larvae need to be moved into seawater conditions and fed tiny live foods, but it is possible.>
They seem to be aggressive towards one another,
<As are virtually all crabs.>
and their requirements go way beyond what the pet store would have you believe.
<Same with Goldfish, to be honest.>
I wouldn't recommend them as a pet for the average person.
<The huge problem is that the "average person" doesn't usually keep pet animals terribly well. How many dogs do you know that get short, infrequent walks? How many parrots do you know living in small cages? How many Goldfish do you know get in bowls or small aquaria? You and I are different in caring about how animals are maintained in the home; the average person often doesn't care all that much -- or perhaps more charitably, doesn't understand how badly they're treating their pets.>
Thank you for any information you can give! Your website is awesome!
<Kind of you to say so.>
Lorie Masi
<Cheers, Neale.> 

my crab... F, really BW... color change... beh.  06/12/09
Dear Crew;
I have a red clawed crab that I have had for almost 6 months now. He always seems pretty happy and forages around a lot for food. I feed him shrimp pellets and the odd tiny piece of orange (which he attacks and drags into his cave to devour). Today I looked at him and he has suddenly gone really red. I mean really red: his legs, his chest, and even some of his back. The little guy has molted twice now and I don't remember the colour change. He seems really active, the water is clean, I don't know if something is
really wrong, or really right. Can you help me?
<Hi Rachel. It's difficult to know whether or not what you're seeing is normal, and the best approach with crustaceans generally is to focus on preventative healthcare. We know precisely what Perisesarma bidens needs to do well: an aquarium with dry land to explore; marine aquarium iodine added at half the normal dose; and brackish rather than freshwater conditions, 6 to 9 grammes of marine salt mix per litre of water being adequate. If you do all these things, your crab should be in good health. If you're not doing all of these things, then it's possible you're seeing some sort of negative reaction. If he's active, that's a good sign, so if you correct conditions in the tank, hopefully he'll settle down and have a healthy life. Cheers, Neale.>

Re: unknown crab, fdg., sys., beh.   4/22/09
I was mistaken when I said that the crab had eaten a nice piece of cantaloupe.
<Banana! Land crabs seem to love banana, the softer the better! Also try small pieces of white fish, ideally lancefish, which you can buy in pet shops. These have bones in them, and the calcium there is excellent for the crabs. Unshelled prawns, perhaps sliced along the middle to make things easier, are also a good source of calcium. Crabs are scavengers, and generally eat anything that's soft or meaty.>
My wife had removed it as it was getting a bit smelly. The crab has not eaten anything since we got her and has seemingly become very weak.
<Review air temperature and humidity; these are essentially like frogs in terms of care, and cold, dry air does them no good at all. Turning the heater up in the water side of the tank can create more warm, humid
conditions in the land side of the tank. Likewise, keeping the lid more firmly secured will help, too.>
She has not moved much in the past 2 days. Maybe she's getting ready to molt.
<You can actually check this: before they moult, crustaceans absorb extra water. When picked up, you may notice they've both bulked up and yet the shell is softer than normal, and may even yield a bit to the touch. They feel less heavy for their size that you'd expect (a tip you using when buying edible crabs, by the way). While the following link refers to Land Hermits, in terms of generalities, it would hold true for Land Crabs too:
So, prior to moulting, the crab will puff up, become softer, tend to hide away from light, and generally become inactive. Moulting starts with the exoskeleton unzipping, and the crab sort of backs out of its shell,
tail-end first.>
I hope so. We would not feel like very good stewards if she dies.
<I understand!>
Already lost one pet this week :-( One of our Fischer's lovebirds had a seizure and died in my hands.
<Oh, sorry to hear that.>
Of course, I have zero history on the crab. Have tried feeding her a variety of foods to no avail. Any suggestions? Thanks.
<Cheers, Neale.>

Odd freshwater Crab behaviour I have a ten gallon tank with low water and rocks for crabs and other crustaceans. I bought some crabs and here's my q's. One: Are the crabs with one large and one small claw  males, and the ones with two small claws females? Two: Today the male??, one large one small claw, climbed out of the water onto the rock and started foaming? or bubbling from his face and doing something, like he was washing?? what is this? He the proceeded to sit then later he did this crazy claw dance, waving his arms around slowly in these rhythmic motions all the way out and then back in, what the heck? Does he have mad crab disease? Three: I put in feeder golds but they seem to ignore them. so I feed blood worms. should I add plants for veg food, or just stay with blood worms and whatnot? Four: The red crab I got has only one claw will his other grow back like at molting or something? Five: What's the ratio on crabs? The same as fish or? i tried here and all over to find good info on their behaviour and i came up empty handed! >> Yes, crabs with one larger claw are more likely males in most species. Crabs have to get oxygen when they are out of the water they will "chew" a small amount of water to mix it with air and get oxygen from this process, that is likely why your crab is foaming. He is waving his claws to show his territory and attract females, so he is not mad. You can feed with bloodworm, but try other foods to see what else your crabs will eat, it varies from one species to another, but most are omnivores. The missing claw should be replaced in the next molt,  I would not worry. For a great website on crabs and other crustaceans check http://www.crusta10.de not sure if it is all in English, but the site owner is one of the most knowledgeable people on the subject. Good Luck, Oliver

Anomalous Crab Question - 10/30/2004 Hello, My little red crabs keep getting on the filter and just sit there like they are in a stream. <Er, do you know what kind of crabs these are?  Can you give me a good description of them?  Size, coloration, markings, anything like that?> I do not see how they are getting up there unless they can swim. Why and how do you think that they are doing this? <The how is the easy part.  Crabs are *amazing* for being able to climb nearly anything....  I wouldn't be too terribly shocked if they were simply climbing the glass!  But more likely, they're finding a way up to the filter intake tube, and climbing that.  Now, as for the "why" of it, there are likely a few reasons.  First, is this a fresh, brackish, or saltwater aquarium?  In what country do you live?  In the US, there are nearly - or absolutely - no crabs sold in the hobby that are truly freshwater animals.  Most will survive in freshwater for a time, but they will not thrive and will not live their full life span.  Moreover, nearly - or absolutely - no crabs sold in the trade in the US are truly aquatic.  All are amphibious, or land crabs that only occasionally venture into the water.  Chances are, your little inverts are just trying to find a way out of the water.  At the very, very least, I recommend you drop the water level a bit, and give them a surface to rest on out of the water.  Try to provide them with a few hidey-holes on the surface to help them feel secure.  Remember, crabs are extremely adept escape artists, and they can and will find any way out of the tank, especially if they're not happy with their setup.  Please be sure you have a tight-fitting lid, or you might wake up in the morning to find a crab cuddling you in bed!  ;) > Thank you Kayce <Wishing you well,  -Sabrina>

Molted Crab - 05/31/2004 I have a Red Claw Crab, he is my first crab and I don't know what to do now that he has molted. His old shell/skin is sitting at the bottom of my tank, I don't know if I should remove the skin or leave it in the tank. <I would leave it.><<Often are eaten, reincorporated into new exoskeletons... necessary mineral content. RMF>> I know Hermit crabs need their old skin to eat, but I don't know what to do with this one. <If it's not gone in a few days, pull it out.  I would assume the crab (or other denizens of the tank) will have made short work of it, by then, but if not, best to get it out.  Wishing you and your crab well,  -Sabrina> Shelly Warren

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: