HCA: Hermit Crab Association

Hi! I wasn't sure which forum to post this in...
One of my crabs went through a molt (his second one in a couple months, it took us by surprise and no one noticed until I got home yesterday -- I've been at college, luckily nothing happened) and switched shells. I keep tons of shells in the cage and switch them out every once in awhile so my crabbies have a lot of options -- but my crab (Herbert) switched to a shell half the size of his pre-molt one. He doesn't fit in it at all, most of his body hangs out of it. I thought if I gave him some options he would switch eventually, but it's been almost two days now and he's still hanging out in a shell that doesn't even cover his back, much less his eyes or legs. I'm not sure why he chose it because there are quite a few shells that are the same shape and the right size, and I'm not sure what to do about it, whether it's hurting him or not. I'm really worried about him, he's not responding when I pick him up like he usually does and he's not very active either. Should I do something? Should I just wait? I'm not sure the local vet knows anything about crabs, and my reptile store is pretty useless. Is he sick?
Thank you for your help.

They may choose smaller lighter shells if they are weak for some reason. Can you answer the questions in the help template in the ER section? That includes all the info we need to get a picture of their environment. We might be able to spot if something is off and causing his issues!

wodesorel wrote:They may choose smaller lighter shells if they are weak for some reason. Can you answer the questions in the help template in the ER section? That includes all the info we need to get a picture of their environment. We might be able to spot if something is off and causing his issues!

1. What kind of substrate is used in your tank and how deep is it?
I use sand, it's 3 inches deep and mixed with a calcium supplement (I also keep eggshells for them to eat in there)
2. Do you have gauges in the tank to measure temperature and humidity? If so, where are they located and what temperature and humidity do they usually read?
Yes; I keep the temp in the 70s and the humidity in the 70s or 80s.
3. Is a heat source used in the tank? If so, what?
I have a heat lamp and also keep my room in the house warmer with a space heater.
4. What types of water are available (fresh or salt) and how is the water treated (what brands of dechlorinator or salt mix and what ratio is used to mix it)?
Both fresh and salt water are available. I dechlorinate naturally -- let the water set for a week. For salt I use a salt water hermit crab conditioner and just follow the instructions on the bottle.
5. What kinds of food do you feed and how often is it replaced?
I give them fresh fruits and vegetables, and cooked meat when I have some available. I change it every day. I also keep food pellets in the cage all the time and some millet (like you give birds, they really like it).
6. How long have you had the crab and what species is it, if known?
I've had Herbert (and his sister) for about a year and a half now. He's a purple claw crab.
7. Has your crab molted, and how long ago did it happen?
Yeah, he's molted once before this, about 4 months ago. And then he just molted again last week, like I said.
8. What type of housing are the crabs kept in, what size is it and what kind of lid is on the housing?
I have a terrarium -- 20 gallons but tall instead of wide, so I have space for the substrate and climbing stuff. The lid is just a chicken wire reptile lid to keep them in, although they can't reach the top. Part of it is wrapped in aluminum foil to keep the heat and humidity in.
9. How many crabs are in the tank and about how large are they?
There are 4. Herbert is the biggest and is about 3 inches, maybe a little smaller.
10. How many extra shells are usually kept in the tank, if any?
I like to keep 15-20 of various sizes in the cage that they can switch into, plus bigger ones for climbing and hiding in.
11. Have there been any fumes or chemicals near the crabitat recently?
No
12. How often do you clean the tank and how?
I try to clean it once a month, and whenever I'm home (about every two weeks) I clean the water dishes and change out the shells and sift the sand. When I clean the cage I replace the sand, wash the walls with vinegar and water, and rearrange the set up so they don't get bored with it.
13. Are sponges used in the water dish? If so, how are they cleaned?
No, I was using them but they got dirty so quickly that I stopped. There are shells in there to help them climb in and out, but not sponges.
14. Has anything new been added to your crabitat recently?
No

Are they burying to molt? If your largest is 3 inches and you have 3 inches of substrate it doesn't sound like they can get completely underground to build thier little molting caves like they need to. We recommend at least 6 inches or enough to cover over your biggest crab three times, whichever is more.

And is it playsand or calcium sand? Calcium sand isn't good for them, it sticks and creates molting trouble. It should be silica based playsand, which is also a lot cheaper, $5 for 50 pounds, and a 20 tall can take 2 to 3 bags for the right depth.

You also say you sift the sand, is it being kept dry? It should be moist enough to shape, like for sand castles. That is how they are able to tunnel and dig. Calcium sand cannot be moistened or it turns into cement as it dries.

If they are surface molting or if you can see them while they are molting, that is probably the cause of the slow down. Each one causes them damage, and eventually they run out of energy to keep doing it.

If you have chlorine in your water then aging it is enough, and it only takes 24 hours. If you have chloramines though, that takes weeks to diffuse and really needs a dechlorinator which also means you can use it immediately Hermits are sensitive to heavy metals so a dechlor that contains that is a good idea anyway, no matter what is in the water. Most of us here use Seachem Prime as it gets all the nasties and only takes a couple of drops.

Strangely enough, hermit crab salt is not enough. Most hermit crab products are not actually good for them. The salt water conditioners won't hurt them, but it also won't help them as it contains the wrong types of salt. To mimic ocean water, which is what they need, it takes a saltwater fish salt like Instant Ocean. One $8 box will last a year or more, and you just mix it up as needed.

The same goes with hermit crab food, many pellets actually contain harmful ingredients. I am not sure which you are feeding but it could be adding to the problem. We have a sticky in Food & Water with commercial foods and which ones to avoid. A good diet of fruit, seafood/insect, meat, veggies and plant matter is important to keep them healthy. In the wild they eat everything!

Most of us here use Seachem Prime as it gets all the nasties and only takes a couple of drops.


The directions for the seachem prime is 5ml/50 gal. That works out to a teeny amount for 1 gal. I have a syringe and it's still difficult to measure .1ml. How do you do that? The bottle doesn't have a "dropper" built in.

It's .1 ml per gallon, or a tenth of a Milliliter. You can measure that accurately out of a syringe, especially 1ml feeding syringes or the really small ones made for insulin if they have a removable needle. I used to ask my vet for extra syringes and they were always happy to provide feeding tips for free, but we ended up just ordering a few sizes online so we wouldn't run out when dosing various meds.

Alternatively, you can purchase a dropper tip online and turn the whole bottle into a self-made dropper.

I personally use an embroidery needle to poke two holes across from themselves in the seal. Easier now that they are using foil! One is for air release so the other will drip, and I mostly use the bottle as a shaker.

wodesorel wrote:It's .1 ml per gallon, or a tenth of a Milliliter. You can measure that accurately out of a syringe, especially 1ml feeding syringes or the really small ones made for insulin if they have a removable needle. I used to ask my vet for extra syringes and they were always happy to provide feeding tips for free, but we ended up just ordering a few sizes online so we wouldn't run out when dosing various meds.

Alternatively, you can purchase a dropper tip online and turn the whole bottle into a self-made dropper.

I personally use an embroidery needle to poke two holes across from themselves in the seal. Easier now that they are using foil! One is for air release so the other will drip, and I mostly use the bottle as a shaker.

I use a syringe but it's still very difficult to get such a small amount. Is it a problem if a little more than that is added?

Not at all! I always give an extra shake to be on the safe side.