Ask Milo – Hermit crab is surface molting

Kendahl asks:

my hermit crab just started molting a few days ago and we put him in an ISO tank but he is completely out of his shell and surface molting. I know thats not good for a hermie but for some reason he just wont dig. i’ve been checking on him and hes still alive and doing fine, hasn’t ate his exoskeleton yet. I’m worried he’s not going to molt properly and die. is there anything I can do to get him to dig underground? or should I just leave him alone?

Dear Kendahl,

It depends what your ISO looks like. If it is pretty bare they can get stressed. If the substrate isn’t easy to dig in that could also be the problem. Can you describe the ISO set-up?

What I have done in the past is dig a small hole in slightly damp sand/ substrate and put the crab and shell in the hole and cover with a flat clam or scallop shell or something you have to create an area for the crab to calm down. A hidey hut made from a coconut shell also works well if you have one.

I’ve had crabs successfully surface molt but this technique has worked for me in the past. One of my crabs then dug down after he had the energy to do so. It is also important that your ISO has correct humidity levels, especially if the crab is out of its shell – that’s where they keep their water reserves.

I have gently helped crabs into their shells only two times successfully out of three attempts (different crabs). Usually if you dip the shell in fresh de-clorinated water and lift the crab gently and curl the abdomen into the shell and put your hand near its eyes it will back into the shell. I have only tried this with strong, healthy crabs – I would be very very gentle or not do it at all if it was going to stress out a crab that had, say, lost limbs due to stress. If you don’t think you should risk helping him into a shell then the other suggestion I have is to offer larger shell that has water inside already, for him to back into.
That has worked for me in the past. They can’t really carry the shell but they have the protection and water reserve.

I hope this helps and please reply with a description of your ISO set-up.

If you don’t have hearing and humidity required you might need to put him back in the main tank with a soda bottle ISO unit over him. Instructions can be found on CSJ – search for ISO.

Your friend in a pinch,
Milo