Hermit Attacking Brain

[Howler]

I found my blue legged hermit attached to and digging into my brain coral and he managed to inflict some harm. I separated them but he went back to feeding on the same bit he'd damaged before.

The hermit shell and brain are about equal in size - almost the size of my fist.

In case the hermit is starving, I've fed him up and am hoping he stays off the coral. He's recently moulted (does this make them super hungry?).

Hermits are so ubiquitous that I presumed them to be 100 percent safe.. any thoughts?

 

[Donya]

There needs to be a concrete species on the hermit before making any formal conclusions. Blue-leg usually means Clibanarius tricolor, but not always.

Hermit crabs will attack corals under two fairly common conditions:
- The crab is not being fed a proper diet (or is starved) and the coral has just eaten. Food is ripped out of the coral, but coral tissue is usually not ingested or minimally ingested.
- The coral has been damaged by something else (stung, diseased, etc.) and is actually decaying a bit, attracting the hermit crab as a scavenger. Diseased/dying coral tissue is not always obvious to our eyes until the condition has progressed quite a bit, but other animals will jump on it much faster.

If the hermit crab is actually ingesting lots of healthy tissue (which I want to emphasize is really, REALLY unlikely if you have a C. tricolor, so look for other explanations before defaulting to this), then you either have an individual with incredibly unusual behavior for the species or a species that is not safe with that species of coral. Abnormal behavior in hermit crabs is often a sign of other health problems. Sometimes it's diet related, but it can also be due to internal abnormalities that the hobbyist has no control over. Of the bajillions of hermit crabs I've had over the years, individuals with tumors and those with chronic molting issues have made up most of the behavioral oddballs.

When you fed the hermit crab:
- What did you feed it?
- Did you observe it eating the food or could it have been stolen by another animal?
- How often is the hermit fed normally?

 

[Howler]

Donya, this is much appreciated. I had fed the coral before the crab episode. The crab has gone the night without again going for the coral.

I'll start paying more attention to crab diet. Previously I'd worked on the basis that they take care of themselves in the tank by scavenging around.

 

[Donya]

Hermits can exist without target feeding in some tanks, but not others. It is entirely dependent on the amount of food going into the tank and how quickly it is snatched up by other animals. Hermits also can't subsist happily on just algae, so even if there is tons of algae and they are eating it, a lack of meaty or other carnivore foods will start to cause desperate and stressed behavior.

A lot of people are hesitant to specially feed CUC animals because of concern over water pollution, which is something worth considering even though the issue is usually overblown. If you are already feeding frozen foods to the tank and it isn't getting to the hermits, try adding a few sinking shrimp or krill pellets to distract the hermits before you feed anything else in the tank. If they show no interest, suck the pellets out with a turkey baster when they start to fall apart and wait a day or two before offering any more. Pellets are generally less polluting in terms of phosphates and such than a lot of frozen foods, and hermit crabs are also able to get to them much faster than lighter foods that blow around easily.

 

[Howler]

Out of interest, here's a pic where you can see the guilty party and damage done (around the middle of the coral one of the "mouths" has been dug out).

 

[Donya]

Wow - well that is no Clibanarius tricolor, that's for sure! Is the blue color on the legs in the photo true to life, and have you got any photos showing the claws as well?

EDIT: actually just saw a photo with a leg exactly like that, so I don't doubt the color anymore. There are a number of photos on the web of the species labeled as Clibanarius longitarsus, but I need to check whether that ID is legit since I'm pretty sure I've seen some contradicting photos with the same label. Anyway, a name will be found.

 

[Howler]

The blue is consistent with the look to the naked eye.

Here's a pic of him waving.

 

[Donya]

After some more looking I will stick by the Clibanarius longitarsus ID. It's a large-ish species, so maxing out with a walking leg length of probably in the 3-3.5" range. The main issue with large Clibanarius species is that they carry more "accidental" sorts of risks than small species. Large Clibanarius can damage things from climbing and falling, and you will want to avoid putting corals in paths that the hermit traverses regularly. They will often try to bulldoze well-established paths before finding new ones, and while smaller hermits can climb over corals without causing harm, a larger animal hanging off of a LPS polyp by a single pointy foot can easily cause tissue damage.

 

[Howler]

Thanks again Donya. I knew when I got the crab that he was impractical but was shopping with my eight year old son; it's theoretically his tank so his views carry some weight as to its contents.

I think another negative element is that they don't get into the smaller nooks to do a proper cleaning job... so you still need the smaller critters.

 

[Donya]

I knew when I got the crab that he was impractical but was shopping with my eight year old son; it's theoretically his tank so his views carry some weight as to its contents.

Large hermits get an unnecessarily bad reputation a lot of the time. If they are cared for properly and the clumsy aspect is planned around, particularly those in the Clibanarius genus work out just fine. I've got a similar stocking situation in my 55gal where I tried to get 24 Clibanarius virescens (usually called yellow-tip hermits), which stay fairly small. Instead, I ended up with 21 of them and 3 surprises that snuck past me, one of which has grown to probably about the same size as your blue stripey guy.

I think another negative element is that they don't get into the smaller nooks to do a proper cleaning job... so you still need the smaller critters.

Indeed, big hermits are pretty limited in what they can reach. Either they are kept well fed enough to ignore stuff that gets out of reach, or, if they are totally desperate for food, they will sometimes make a mess trying to get to whatever it is by digging in the sand and such.

 

[Howler]

To help with tidying up those hard to reach bits I bought a cleaner shrimp but he didn't survive the transplant into the tank - nevertheless, it served as a meal for the crab, which ties in nicely with this thread. I got him on camera - check out the link.


YouTube link: hermit feeding

R.I.P.

 

[Donya]

Try a silverside at some point - he'll go nuts!

How did you acclimate the shrimp? While it's not impossible for shrimp to have a shrimpy heart attack in the bag on the way home (has happened to me once; shrimp are fragile things), most rapid shrimp deaths are due to rushed acclimation, exposing the animal to different water parameters too rapidly.

 

[Howler]

I hooked up a drip line from my tank to his bag. The flow rate was around three drops per second (too quick?) and I kept it up for 40 minutes. All my water parameters were 100%.

When I got ready to put him in the tank he was already dead. I didn't check whether he was alive when I started the drip, so I don't know if he even made it to my house alive. At the shop he looked in fine spirits - I'd asked how long he'd been in the fish shop tank and it was five days, so I'm pretty confident that he was stable and hadn't just finished a trans-Atlantic flight in dodgy conditions.

Poor guy. I hate that he died.

 

[Donya]

The rate may have been a bit fast. I usually drain part of the bag water and then do 1 drop/sec or very slightly faster and spread it over 2 hours, but it's also dependent on how different the bag water is from the tank. That can be overkill if the bag is really similar to the tank. On the other hand, it can take hours at a slow drip, emptying the bag a few times if your tank has a sg of, say, 1.025 but the bag is at 1.018 (scarey low, but some stores have it there! It's always a good idea to check sg and pH on the bag water). Usually they don't die quite that fast though from rushed acclimation, so that makes me lean towards it being something like that the shrimp was bopped too hard with a net by accident at the store when being transferred from tank to bag. It could also be that the shrimp was about to molt and the timing was just ill-fated. If they are about to molt and then get jostled/stressed, they will sometimes try to delay the molt and then die suddenly as a result. It's actually a big enough problem with coral banded shrimp that I won't get one of those these days unless I see a shed skin in the tank. It's not as big a problem with the Lysmata cleaner species (skunks are in that genus), but isn't a complete non-issue either.