15 Apr 2008

Why Did My Fiddler Crab Die?

Dear Blue Lobster:

We volunteered to take the Fiddler Crab from my son’s in-class science project. The crab appeared to be doing well, eating and taking some dips in his “pool” of salt water. We changed his water and his food regularly. He burrowed through the substrate mixture (sand and humus?) in the bottom of his cage – and often slept under his see-through pool (the container the class used to provide salt water).

He was more lively than usual over the weekend – climbing up and over the flat seashell, ½ coconut shell, fake plant, and swimming pool.

Today, he appears liveless – he is upside down in his cage and has not moved since we woke up this am. There doesn’t appear to be any new appendages or a new crab anywhere in the cage.

Can you tell me how to tell if he is dead, molting, or already molted?

This mom is unfamiliar with fiddler crabs and wants to make sure we know what “Thunder” is doing, before assuming him dead.

Thank you.
Linda Adams

Dear Gentle Sir:

Thunder, from your description, appeaears to be dead. I am so sorry for your loss.

A crustacean's living conditions general health affect its ability to molt. Sick or otherwise unwell crustaceans molt abnormally and may not molt at all, and if a crustacean can not molt when it needs to, it will die.

When an illness or stressful situation limits the crustacean from molting, it will literally explode in its shell. The cracks induce sepsis from the numerous infectious agents now able to attack the soft inner body.

In Thunder's case, it appears that his living conditions were suitable generally and he was in more or less robust health, so what other factors might have been at play?

It is possible that, despite Thunder's well-kept tank, the stress from too many visitors kept him feeling unprepared for a molt. Did one of his numerous visitors offer him something potentially poisoinous?

One must keep in mind that Thunder might have been nearing the limits of his lifespan. You don't mention a physical description, but most Fiddlers live no more than two or three years. One species, Uca senex, lives to be seven years old in some cases, but that is an exception to the norm.

It is possible Thunder had scuttled through the greater part of his life when you inherited him, and either his own old age or the stresses of students and moving to your residence finally knocked him off.

One must not blame onesself for such tragedies, however; only in dealing face-front with crustacean rearing and death does experience build. Check out some crustacean or aquarium literature from your local library and consider your time with Thunder. The next little friend you take in will benefit.


Anonymous said...

yes the same thing happed to my daughters crab he was doing fine now he is in the tank not moving at all :(

Anonymous said...

my mom bought me a crab the other day and I got on the computer last night to get information about them. And when I opened his tank to get some fresh air he's big claw was missing and so was a little point of one? It was so sad. He was tipped over and I thought he was still alive because he was moving but I guess it was just nerves. email me at riddleghost@yahoo.com please

Anonymous said...

I know this is very late since the last post, but I am really curious as to what happened to my crabs and I couldn't find any other source. Sorry.
So I had two fiddler crabs in one tank and for about 2 months they were doing fine, until today. I looked into the tank and I saw a horrid sight. My female crab seemed to be ripped to shreds. The top half was detached from its legs...
My male crab seemed to be standing normally, but when looked at closer, I could see that his underside was peeled back, like it was hinged open. It was lifeless. I fished them both out of the tank. I'm extremely confused as to what happened because they both seemed to be doing fine in their environment up until today. They seemed to just explode. It was like a massacre.
Any help would be greatly appreciated.
If you could email me at nick17260@hotmail.com

Anonymous said...

My fiance and I bought several of them, but our male died today. :( my condolences to you all for your similar losses.

Anonymous said...

Two of my fiddler crabs are upside down in my tank. My mom and I think that they fought with each other... later on, one of the "dead" crabs had white liquid streaming out of the back shell. But weirdly, the crabs kept on moving a little bit; they either moved their claws or legs, or their eyes and mouth moved....but my family decided to trash them. HOW SAD!!! :'(

Anonymous said...

I have a fiddler crab and she seems to be doing very well during the day but at night she stays in one spot and she will not move. Is she sleeping or molting or dying? Her face looks very old and kind of looks like her shell might come off, but she wont move. She is underwater right now. what should i do? is this normal?

Anonymous said...


Anonymous said...

ok so i'm not alone. my fiddler crabs have been doing great, but when i returned home from work i noticed that both of them were sitting on there butts, they purposely lodged themselves in between things so that they would be sitting, they werent on there backs or there bellies but with there faces toward the cieling looking like they were in the process of dying, but at a closer look the female was still moving it's mouth and an occasional claw so i let them sit for awhile, then i got worried so i poked them both with my finger and considering they are very skittish creatures and they didn't move a muscle i quickly got them out of there tank and into a new fearing something in the old tank was killing them, i read up and found out there brackish so now there in a brackish beach front tank, i set them on the sand and the male is doing kinda better it's moving more but only when i poke him, and the female insists on sitting on it's butt looking at the sky, but it uses every last bit of it's strength to do that and i fear it will not make it thru the night, please someone tell me whats wrong and why this is happening all the sudden out of no where.

Anonymous said...

no reason to have fliddler crabs in your tanks...they usually die for reason....sucks! it's been 2 years Ibeen buying same thing and they die..they don't last longer than my fish....=)

karl olsson said...

i had two mangrove crabs in a niece perfect tank but after they Had fight both of them started to get slow and in a week ore two they both dies sadly one of them lost three legs and the other one got its back legs paralyzed since it couldn't move them

Anonymous said...

I bought 2 male fiddler crabs about a month or so ago,my little male died :-( and the big one is doing well so I replaced him with a female fiddler which we've only had for a few days,I had them in my 60 gallon tank with all my fish they were doing great then I read on the internet that the crabs need land 2 or they would die,so I got a 10 gallon tank and I made them a new crabitat with 1 side being dry land which sloped down to a small piece of land with small water that lead into deeper water about 2 inches deep or so,I put my bubbler in the water so its getting fresh oxygen as I read well I checked on them through the night an they were doing fine so I thought well I went to bed an got up this morning to get the kids off to school and I go in an check on the crabs an my female is dead :-( once again the big male is still alive,so I'm wondering what to do with him should I leave him in the tank or out him back with my family of fish tank,I'm confused to what happened to both my smaller crabs and I need to know exactly what to do...please any advice would be great....thanks a bunch
You can email me @ moonstone2009@yahoo.com

izzy098 said...

Ok, so I had two fiddler crabs. They were both doing fine moving around having a good life. I brought them home from school male- cha cha and female squirt. They were doing well in a brackish water community with decorations and everything else I spent 90 dollars on, I came home one day and my female crab was tired over on its back. I thought it was dead but left her for several hours untouched in case she was molting. She didn't move so when i scoped her up to discard her I saw that her belly was almost detached from her and legs scattered around her. Her companion was losing many legs also. I thought that maybe they had fought, but why would they? Now I only have the male left and he seems inactive and just stays hidden and immobile all day. What should I do? HELP!!!!!

Anonymous said...

My female died today. I have four in a ten gallon tank. 2 males and 2 females. The second day i had the first pair of the male and female her arm had been ripped off so she only had one claw. About 3 weeks later i found her the next morning on her back white as a ghost and belly flap was open. Not sure of it was old age or stress or what. The other 3 seem fine. Their tank has half sand and half brackish water and they eat regularly and have clean water. Im gonna go get another female probably a small one cause its probably younger. Im thinking it was old.

Anonymous said...

i have 2 fiddler crabs and last night i went in and looked in their tank and i seen a molt from on of the crabs and i found a crab on its back i could see its bellie i tried to poke it with a plastic spoon but i wouldnt move so my mom and i had a crab funeral was it even dead or just molted?

Anonymous said...

i have 2 crabs both male and i seen a molt in the tank so i scooped it out when i did i seen a crab on it back in the water i poked it with a plastic spoon then i scooped it out was it dead or did it just molt? it wasnt moving

Anonymous said...

Lost our family fiddler "Mr. Krabs" today.

Seems he had been hiding in a seashell from out overly grown and hungry goldfish. The goldfish seems to have caught him during a molt since I found his claw and shell in one corner and the poor guy lifeless on his back in the other with his small arm missing.

I guess he had to come out to molt and was vulnerable. Not sure why losing the limb would have killed him. His large claw was already hardened this morning so I am only speculating on what transpired.

We have a pleco, bettas, harlequins, and this damn goldfish. It was just a feeder fish the kid's saw and wanted because of his pattern. He has become a voracious eater and sucks and mouths at everything while it zips back and forth ALL day.

It's nearly 5-6 inches now and I haven't found a Koi pond to toss him into.

Not sure what to do with him but I was putting fish food in the crabs favorite sea shell as a temporary solution since he eventually got terrified of the aggressive goldfish.

We've had Mr. Krab's for about 6 months.

I'm going to put the GF in a bucket and get a new pair of Fiddler's. I'm also going to build a ladder with a little shelf for them to get dry land. He never tried to escape and was happy until the GF got too big.

Will make sure to have lots of hiding places too. So sad. We'll miss you little guy!

Anonymous said...

I have four fiddler crabs and three fish, there are two big males and a little male and a female, they have been doing fine with their environment, doing their little crab dance and everything, we've had the small male and female for a few weeks and we just got the two big males, they get along well enough with the occasional territorial dance, we found the female belly up this morning missing an eye, was she molting or dead?? Email me at amcglone922@yahoo.com, I'd really like to know, we did flush her but then some sites are saying she was molting but she didn't even move when we poked her with the fishing net

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