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.