Hermit Crabs Just Disappeared

takey · Jan 13, 2023

Hey Yall, I have an interesting question, and I was wondering if I could get some input on it. So I had five hermit crabs in my 15gal Fluval flex, and it's been around three months since I added them. About a month ago, around December 20th, they just slowly started disappearing for no obvious reason. One thing I could think of to explain one of them missing is that it was molting and, I'm assuming, hid in the sandbed, and I might have crushed it while re-scaping the rockwork, but as for the other four, I have no idea where they are or what happened to them. I have a tux Urchin, two clowns, and some coral, so nothing ate them, and I haven't had an ammonia spike, so I'm not sure if they are hiding in the sandbed molting or hiding in the sandbed dead. :/ If anyone has any ideas about where or what might have happened to them, I would love to know.

blaxsun · Jan 13, 2023

Did you find 5 empty shells? If not - they're still in there. Somewhere...

Dburr1014 · Jan 13, 2023

Probably climbing around the rocks.

RabidDragon · Jan 13, 2023

Do you have any empty shells at all? they do grow and need larger shells to swap into.

takey · Jan 15, 2023

blaxsun said:
Did you find 5 empty shells? If not - they're still in there. Somewhere...

It seemed like they would hide somewhere as if they were molting and drop their shells and then I would never see them again.

blaxsun · Jan 15, 2023

takey said:
It seemed like they would hide somewhere as if they were molting and drop their shells and then I would never see them again.

When they molt they'll usually reoccupy the same shell unless something more desirable is available. When they die (rare), they will leave the empty shell.

Hermie · Jan 15, 2023

My tank is 23 gallon display and about 3 or 4 years old.
I've had anywhere from 1 to 6 hermit crabs at a given time but the end result is the same, one hermit crab will kill all the others.

I suggest that the other hermit crabs were killed. You can tell they are fighting because you will hear a "clink clink clink" sound of them bashing each others shells.

Nano sapiens · Jan 15, 2023

Hermie said:
I suggest that the other hermit crabs were killed. You can tell they are fighting because you will hear a "clink clink clink" sound of them bashing each others shells.

Maybe...

I've had 4 or 5 hermits whittle down to one 'King of the rock pile' in a few months, too...and then again, I've had three hermits together for years now.

This is one of those 'it depends' (on who knows what) things in reef keeping.

JasonVH · Jan 15, 2023

They would have no problem hiding in those rocks. Especially a small species like blue legs. I've a 29 gal with 20-25? of various species. One species is rarely seen despite there being 5 of those. Another species- scarlet hermits and not so small sized either- I never see for a solid month or two. So long I forget they're in there until "whoa, hey there you are" moments. Even the fair sized blue knuckles and halloween hermit crab can be out of sight sometimes or for a little while.

It helps to have extra shells. AND they be of the right kind and sizes of shells. The different species have very clear preferences. Particularly the orientation of the shell opening seems important. Side ways orientation- trochus for example- have been refused by all. Not having extras or the right kind of shells probably leads to intense competition.. I have lots of extras in the tank and afaik, there has either been no killing or very occasional one in this set up.

If the tank is new/mostly or very clean, it helps to occasionally feed with the hermits in mind. I occasionally drop in a bit of nori wrapped around something with rubber bands and let it drop to the bottom. They go nuts for it, immediately coming out of the rockwork. It's not a worry to deliberately feed them, they are perpetually hungry and will continue their cuc duties but probably with more energy/better overall health(in case of 'too clean tanks').

Hermie · Jan 16, 2023

Nano sapiens said:
This is one of those 'it depends' (on who knows what) things in reef keeping.

Probably the sex and species of the crabs.

Show me the counter evidence and Ill change my mind.

Nano sapiens · Jan 16, 2023

Hermie said:
Probably the sex and species of the crabs.

Show me the counter evidence and Ill change my mind.

These three were together for about 2-3 years.

The Red legs disappeared at close to the same time and were then replaced by two Blue legs sometime in 2021 and all three are still in my system.

Perhaps the Halloween is refereeing for the others