HCA: Hermit Crab Association

Hey everyone. I’m new to this community but I’ve owned hermit crabs for about 4 years now. I started noticing some strange behavior about 6 months ago but it was nothing too concerning until now. I had three crabs almost a year ago. Two mediterraneans and one Ecuadorian. The two Mediterranean’s (Bong Water and Young Man) were my first crabs. Mathers (my Ecuadorian) was not introduced to them until about a year after I got them. I noticed right away that Young Man (a typically docile crab) was very aggressive towards Mathers. He tried pinching his eye stalks and antennas, pushing him off of high objects, and tried to steal his shell even though he was too big for it. The behavior calmed down after a while but Young Man never became fond of Mathers and still displayed micro aggressions periodically. One day about a year ago after 2 years of living together Mathers (an exceptionally friendly crab) decided to eat Young Man out of his shell and wear it around for several days before changing into a proper sized shell. I was shocked to say the least. I immediately checked all of their food brands to ensure that it wasn’t due to a vitamin deficiency. The food I had then and have presently has everything they need so I know it wasn’t for nutritional reasons. The shell he took from Young Man was much too big so I know it wasn’t over housing issues. After searching for answers I couldn’t find anything. To this day I question if it was an act of revenge after 2 years of being bullied since I couldn’t find any logical answers. Almost immediately after eating Young Man, I noticed that Mathers and Bong Water started to be more aggressive towards each other. Mathers would approach Bong Water in a normal fashion and Bong water would try to either get away from him or slap him with his antennas. It was a strange sight to see since Bong Water is my alpha crab and is significantly larger. This behavior calmed down but I noticed that Bong Water progressively interacted less with Mathers. Now almost a year after Young Mans death Bong water has seemingly reenacted the exact situation that happened. Mathers had buried himself to molt and the next morning I woke up to see Bong Water crammed into Mathers tiny shell. He wore it for two days before changing back into his favorite shell. The strangest part about this is that I could hear something under the dirt moving against the glass when Bong Water was no where near glass. This second incident happened about two weeks ago. I’ve been crossing my fingers that Mathers is still alive under the dirt but I no longer hear anything out of the normal. Bong Water is now presumably alone. I want to get him another tank mate but I can’t figure out why any of this happened and I don’t want to subject another crab to such behavior. I know I need to move fast though. Today he’s started to be more lethargic but it’s not near his time to molt. He exhibited the exact same behavior patterns before when he was lonely (right after I got him he lived alone for 2ish weeks since he came from the fair). I’m not sure what to do here. Was this all a strange unavoidable incident or is there something I’m doing wrong?

Tank size: 40 gal

Substrate: coconut fiber eco earth

Food: Hermit Grub premium hermit crab food (I have 8 different complete meal types of this brand as well as coconut and flower treats)/ fresh produce periodically/ fluckers calcium supplement

Heat: stays between 80-90 degrees Fahrenheit. A back wall heater on only half the tank

Water: two 4 inch deep water bowls. One salt and one fresh water.

Humidity: stays between 70-80

Extras: I have four different hiding spots in the tank, a climbing wall, a hanging net, and moss. However, the moss was not introduced to the tank until 2 months ago.

Also I put this in the wrong area and I apologize for that


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Hmmm. We have a purple, Triple H and an E, Gunshow and they also seem to have their spats from time to time. They will push, shove, grab, bat antennas, and stare each other down every few months. Ours seem to have their spats after molts. Perhaps it's a dominance thing thinking one becomes the alpha then the other resurfaced? Does the aggression seem to follow molts with you? Does it seem to happen around food dishes?

I would try adding some more calciums. If you are only offering one type they may be tired of what they have. Our crabs go crazy for crab exo. That can usually be purchased in garden areas.

If the aggression is around food dishes you may need to add another dish and keep them in opposite sides of the tank.

Do you have any wheels or saucers in your tank? If you don't you could try adding a wheel for enrichment and exercise. That may help curb some pent up energy turning to aggression.

Hopefully these suggestions will be of some help to you.