HCA: Hermit Crab Association

My large PP, Moose, dug down last night and I suspect is planning to molt. Now that I think about her behavior in the past weeks the signs were there. My question is on timing. I adopted her last September and her only molt with me was from 1/7/2011 to 3/2/2011, so the start of the molt was 5 months ago. I thought it was normally longer between molts for a large. Since she's my biggest one I don't have any other point of reference.

Also, I noticed that the substrate that she piled up where she was digging is way too dry. My substrate is 9" and must be dryer below the surface. My humidity is 80 to 82 and I spray about a quart of water on the top layer twice a week to account for drying from the lights. What would be the best way to safely get more water down deeper knowing she is molting, as are a couple others (and I don't know the others molting location? I'm hesitant to pour water in anywhere. I was thinking that I should spray the top layer pretty heavy every couple of days, assuming it will soak through to the lower layers. Thoughts?

I just did a weekly clean of the tank and stuck my finger down in the substrate. The hole held without collapsing down 3" to 3.5" (as far as my finger would go). I decided to spray heavily and sprayed about a half gallon total all over the surface. Apparently Moose was not very far down and the spraying irritated her and she came back up. Still interested in thoughts on checking the moisture level all the way down with 9" of substrate and how to moisten it, if needed, without chancing issues with other molters.

Moose digging her way back out.


Moose ticked off and sitting on the bridge covered in wet substrate. Curly is getting away from the unhappy Moose (upper left).

I don't really know what to suggest. I usually have 10+ inches of substrate and I've never really noticed the bottom drying out. Every deep clean I've had (except this last one) the sand at the bottom was still sand-castle consistency and smelled nice and beachy. This last deep clean I discovered my built in pools were leaking and the last few inches of substrate was too wet and smelled rotten. In my crabitat the sand that dries is just the top layer under the heat lamp and a bit along the back edge near the UTH (which is on the back glass, not on the bottom).

I've seen others recommend using your finger or a pencil to poke holes in the corners and dumping water there now and then. This method always worries me.....too easy to flood I would think and what about molting/underground crabs? The only other thing I can think to suggest is if you ever notice all of your crabs on the surface at once, take that opportunity to thoroughly mix the substrate......but if you have more than a few crabs this is almost impossible. Hope you find a solution that's safe for your molting crabbies.

I'm starting to wonder if the dry sand was what was piled up from the top couple of inches and if my problem is near the top. I've had crabs molt and I know they are making caves because occasionally I see one against the glass. If so, I can probably resolve that by spraying a sprayer full of water across the surface every few days for a week or so.

Not a good picture, but here is Mickey in a cave about half way down, so 4" to 5" from the surface.

If they still can form caves then I'm sure it's fine. I wonder if the substrate your crab dug out dried out after it sat on the surface for a while? A good spray should do it.


Also, I forgot about your first question about frequency of molts for a large. That does sound like your crabby is going down earlier than "normal". Does she have any damage or missing limbs? They'll often molt sooner if they need to repair themselves. Are you sure she actually molted the first time? Also, she may just be digging for the fun of it and not actually molting again. I've noticed my large crabs usually molt once or twice a year.

I'm pretty sure she molted before. She stayed down 2 months and although she didn't look much different, she had sharp little toes. To my knowledge she doesn't have any damage. She may just be digging around, but she has been shell shopping pretty regularly for the past week and did dig down for 1 day about a week ago. I did adopt her and the tank she was in had substrate only about one and a half times the depth of her shell. If it had been a while since she molted before could she then maybe molt again sooner?

If your substrate is that deep and the top layer is still a good dampness for caves/tunnels I wouldn't worry about substrate deeper than that. The top couple inches is what would be evaporated first. Most crabitats are some form of enclosed environment so even some of the water that does evaporate ultimately condenses and ends up back in the tank.

If you think about digging a hole outside, the top layer of dirt can be dry, but deeper is almost always damp. I would actually be more concerned about flooding the lower reaches of the substrate by over-watering rather than it being too dry.

Thanks. I can check the bottom through my stand and last time I looked there was no water. I have insulation there so I don't check all the time. I don't pour water into the substrate, unless I spill a little when lifting out a water bowl. I just spray about a quart of water on the top layer once a week, plus I have a Reptifogger.

Just an update. Moose has been up and down since early June. Digging one day and then coming back up the next. She sure has made a mess in there since she is a large! I keep having to fill in holes that are 4" deep so the little guys don't get trapped. She dug down 2 days ago and has stayed down so maybe she does really plan to molt.