Hermit crabs are not just exotic animals -- they're a very sociable bunch. Because we interact with them differently than we do with more mainstream pets, it's easy to forget they possess their own unique personalities. Like the rest of us, sometimes their personalities will clash.
Normal Hermit Crab Behavior
If you have a hermit crab habitat -- otherwise known as a crabitat -- with more than one crab, you've likely seen them engage in playful behavior. It's normal for hermit crabs to crawl over each other or have pushing contests and feeler fights. Though this may appear to be aggressive behavior, to hermit crabs it's a way to get to know their housemates and to establish the pecking order in their crabitat.
A crab's shell is more than a home; it protects the crab's soft abdomen, helps maintain a proper level of moisture and protects against predators. Sometimes a crab will take a liking to a housemate's shell despite the fact the other crab is wearing it. Shell fights, as they're known, are usually accompanied by chirping noises from the aggressor, who grabs the other crab's shell and pushes it back and forth. The fight escalates when the victim crab retreats into his shell and tries to protect himself with his grasping claw -- often hermit crabs would rather give up a limb than a shell. Other times the victim crab will give in easily and take up residence in the shell abandoned by the aggressor crab. If you see shell fights happening in your crabitat you should intervene and put the aggressive crab in a container that has a variety of shells for him to choose from. Use different sizes, shapes and weights of shells to give the unhappy crab ample opportunity to find a shell he likes. You can do the same for the victim, who might recuperate better in new digs after his ordeal. He'll decide on his own if you make the opportunity available.
Dominance or Aggression?
If a crab is acting aggressively but doesn’t seem to be trying to take over another crab’s shell, it could be that the crabs are establishing the hierarchy in their group. This isn’t unusual if you’re adding new members to the crabitat. Chirping from a crab is a signal that it’s responding to aggression or that he’s highly irritated with a housemate. If that’s the case, isolate the more aggressive crab in a comfortable habitat of his own. Make sure he always has access to shells. Spend time talking to him in a soothing voice and giving him treats. He may be having a hard time adjusting to his space -- particularly if he's new to the habitat -- or to another crab. Allow him back in the habitat with other crabs when you're around to supervise him, gradually increasing the time he spends with them. It can be helpful to rearrange the group habitat, and his, while you allow all the crabs to interact outside of it in neutral territory.
Caring for Victim Crabs
If one of your crabs has been injured by an aggressive housemate, isolate the victim. Chances are he's lost his shell, so provide him with one that is similar in size, shape and weight. Rinse his abdomen to remove sand, then place him and the empty shell into a glass cup together. Put the cup in the isolation tank and leave him alone for a while. This will keep him from wandering away from his shell, conserve his energy and encourage him to take up residence in the shell you've provided. Keep him isolated in a warm, moist area and give him time to recover on his own.
Minimizing the Risk of Aggression
Habitat can play an important role in minimizing the risk of aggression. If you have a lot of crabs or a particularly aggressive crab, try a larger tank or separate your crabs into two separate tanks. Like other animals, hermit crabs will feel safer if they have areas where they can go to hide from predators. Flower pots, cups and bowls that won't chip paint into the habitat make good caves for hiding. Having a wide variety of empty shells available will help minimize the chance of shell fighting among your crabs.
- The Crab Street Journal: Identifying and Addressing Aggression in Hermit Crabs
- The Daily Californian: Hermit Crabs Show Social Aggression for Survival, Study Finds
- Naturally Crabby: Shell Fighting in Hermit Crabs
- Hermit-Crabs.com: Behavior and Aggression: Why Does My Crab Act the Way It Does?
- The Hermit Crab Patch: Friends Are Important
- Hermit-Crabs.com: Hermit Crab Sea Shells: Picking the Perfect Mobile Home
Hermit Crab image by Bobbybigfish from Fotolia.com