hermit crabs aggressive towards each other

Why Do Hermit Crabs Attack Each Other?

Hermit crabs live in large colonies in the wild, often up to 100-strong. This shared living space can lead to confrontation over shells, territory, and other issues. So, hermit crabs will attack each other on occasion.

Hermit crabs playfight to determine a social hierarchy. This involves antennae wrestling or pushing contests. Fights become more serious when competing for shells. This process can be peaceful, but may turn aggressive. In such cases, hermit crabs will need to be separated.

Most hermit crabs are docile and calm by nature. Discover the warning signs of aggressive behavior and understand any reason behind it. This way, you can take steps to help your hermit crabs serenely co-exist.

Are Hermit Crabs Aggressive or Docile?

Hermit crabs are regarded as docile animals. They will rarely attack without provocation. Even then, hermit crabs prefer to avoid confrontation, preferring to hide in their shell to becoming embroiled in conflict.

This does not mean that hermit crabs are weak. They have pincers and know how to use them. If a hermit crab pinches you, you will know about it. This means that they may also end up hurting each other.

Like all animals, hermit crabs will fight sometimes. This doesn’t mean they should live alone. Hermit crabs are social, living in large colonies in the wild. When you put this many hermit crabs together, then conflict will always arise.

Hierarchies of dominance and disagreements will need to be settled. This may result in fighting, but this aggression is rarely life-threatening. In most cases, they prefer to settle their differences amicably.

Why is My Hermit Crab Aggressive?

While most hermit crabs are gentle, it is by no means a guarantee. Some are cantankerous and pick fights for seemingly no reason. This is especially common in hermit crabs that spend prolonged times alone.

Despite their name, they dislike solitude. The term ‘hermit crab’ refers to the fact that these animals carry their home on their back. This creates a sense of social dependence. They grow anxious when alone.

This is primarily because they need to change and upgrade shells regularly. As these animals prefer shells previously occupied by other hermit crabs, they need company. Additionally, they are at the bottom of the food chain, and there is safety in numbers.

Nervous hermit crabs often become aggressive. While they rarely launch unprovoked attacks, they will attack in self-defense. The more time they spend alone, the more fearful they become.

So, are hermit crabs aggressive toward each other? They can be. It is important to understand what hermit crab aggression entails. They often playfight for fun. Hermit crab mating can also resemble a fight.

why is my hermit crab aggressive?

Hermit Crab Fighting Behavior

Hermit crab fights take four core forms. Three of these are normal and natural interactions. Let these events unfold as nature intended. Captive hermit crabs need to embrace their nature.

You only really need to get involved if hermit crab fights are growing vicious. Many conflicts between them are kept civil. If hermit crabs are becoming boisterous, while attempting to cause bona fide damage, things have clearly gone too far.

Feeler Fights

All hermit crabs have antennae, also known as feelers. It’s common to find two hermit crabs entangling these antennae. They may even appear to wrestle with their feelers. This is normal behavior.

Feeler fights are sometimes not even fights at all. Hermit crabs use their antennae to gather information about each other. These antennae pick up on smell. Consider how dogs sniff each other for an idea of why hermit crabs entwine antennae.

Some will engage in feeler fights as a test of strength. Think of this as hermit crab arm wrestling. This activity is used to decide upon a social hierarchy. All hermit crab colonies have an alpha. A feeler fight will help decide this status.

Equally, a feeler fight may just be a recreation for hermit crabs. Like many animals, they sometimes playfight for fun to pass the time. It is rare for a feeler fight to progress into anything more than a shoving match.

Pushing Contests

A little pushing and shoving are often how hermit crabs play. It’s a test of strength that is common in the animal kingdom. This play helps hermit crabs decide who is dominant and who is more submissive.

Pushing is a way for them to test the boundaries of play. Hermit crabs may also climb over each other. They even flip each other over as part of the game. Ideally, they will help each other up afterward. Hermit crabs can get stuck on their backs.

As discussed by Behavioral Ecology, shoving matches can escalate. This is most common when the hermit crabs are assessing the quality of a rival’s shell. If both hermit crabs are taking it in turns to push each other, there is no problem.

If one hermit crab is chirping loudly, it is a warning that the pushing is growing aggressive. Equally, a frightened hermit crab may retreat to hide. In this instance, try to separate them before play becomes bullying. If physicality is one-sided, it is not fun for both hermit crabs.

Shell Rapping

Shell rapping is the most common form of hermit crab conflict. This behavior occurs in the wild but is more prevalent in captivity. Shell rapping can be a peaceful and respectful negotiation. It can quickly escalate into a physical duel, though.

Shell rapping begins with one hermit crab (which we’ll call the aggressor) approaching the shell of another (the resident). This occurs because the aggressor covets the shell of the resident. It wants this shell for itself.

The aggressor will knock against the shell of the resident. It may use its legs or conduct a more volatile knocking of one shell against another. This action could have several consequences.

  • The resident leaves its shell to see what is happening. The hermit crabs wrestle, with the winner claiming the resident’s shell.
  • The resident ignores the rapping. The aggressor tries again with increasing force until it receives a reaction.
  • The resident vibrates within the shell. The aggressor sees this as a display of strength and walks away.
  • The aggressor grows weary of waiting for a response and tries to tear the resident from its shell.
  • The aggressor gets bored of rapping with no result and looks for a different shell.

Shell rapping itself is not something to stop. Hermit crabs need to resolve these differences for themselves. If they can do so diplomatically, everybody wins. If the shell rapping leads to aggression that could result in injury, the hermit crabs must be separated.

Pulling from Shell and Pinching with Claws

If you spot this behavior, you must separate the hermit crabs at once. There is nothing fun or playful about these actions. An angry and aggressive hermit crab may attack the eyes, legs, or soft abdomen.

Of equal importance is preventing hermit crabs from forcefully evicting rivals from their shell. This is rare but can occur, especially if a hermit crab has just molted.

Hermit crabs will do whatever it takes to avoid being shorn of their shell. Some hermit crabs will shed their limbs and hide deeper in the shell. Others will fight back, which only aggravates the conflict.

Why Do Hermit Crabs Fight?

There are six primary explanations for hermit crabs to come into contact with each other. Knowing what incites such behavior means that you can take action to prevent it from recurring. All hermit crabs will appreciate your intervention in this matter.

Unprovoked Aggression

As previously discussed, some hermit crabs are just antagonistic. The victim of an unprovoked hermit crab attack will usually try to ignore it. Most will respond to aggression by hiding in the shell.

Watch out for bullying among hermit crabs. If a larger hermit crab gives a smaller counterpart a hard time, it will only go ignored for so long. This is unlikely to end well for the smaller combatant. As per the Journal of Ethology, size is an advantage in the conflict.

Try to understand why a hermit crab is acting aggressively. It may be in pain or another form of discomfort. Alternatively, it may be struggling with life in captivity. Not all hermit crabs cope well with life as a pet.

If you have an aggressive hermit crab, give it periodic time outs in a separate enclosure. Most hermit crabs dislike living along, but some may prefer the space and privacy. Give the belligerent hermit crab every opportunity to prove that it can live with the company first.

Shells

As discussed under shell rapping, shells are a regular source of conflict for hermit crabs. As per Proceedings of the Royal Society of London, shell exchange does not need to be antagonistic. If both hermit crabs are willing to trade, this will be a peaceful exchange.

Sadly, diplomatic negotiations are far from assured. All hermit crabs want the best possible shell. That means a shelter of appropriate size, mobility, and sturdiness. Dominant hermit crabs consider themselves worthy of the finest shell in a tank. Current residents of a superior shell are unlikely to give it up without a fight.

Reduce the risk of shell fights by providing a constant supply of new shelters. You will notice that your hermit crabs line up to try these new shells on for size. In this instance, a mutually agreeable outcome is likelier. Hermit crabs will not miss a shell they have never inhabited.

Alpha Status

As we have intimated previously, a social pyramid is important to hermit crabs. Whether it contains two hermit crabs or ten, every tank will have an ‘alpha hermit crab.’ These dominant hermit crabs enjoy their pick of shells.

Ethology confirms that hermit crabs remember their place in a pecking order. New attempts at being dominant may be periodically launched, especially after molting. Most of the time, though, hermit crabs are respectful of the established hierarchy. 

Territory

Hermit crabs may fight over territory. Watch your hermit crabs in their habitat. You’ll likely find that all hermit crabs have preferred locations. If rival hermit crabs enter a claimed space, they will be challenged.

This becomes more prominent in smaller aquariums. Hermit crabs may be tiny, but they still need plenty of space. Your pets likely started life in the wild. They are used to having an entire beachfront to explore.

10 gallons is the minimum size for a hermit crab enclosure. If you are keeping multiple hermit crabs together, upgrade this size. A tank of 20 or even 30 gallons will reduce this territorial squabbling.

Mating Privileges

Hermit crabs do not have a mating season dictated by the calendar. Female hermit crabs are typically more receptive to mating immediately after molting. Oftentimes, males display their interest in mating with females by gently rocking their shells.

The choice to mate will always lie with female hermit crabs. They are picky about who they breed with, especially in captivity. The Journal of Crustacean Biology confirms that males never force the issue. If a female shows interest, the male will guard her jealously.

If other males attempt to approach the female, regardless of intent, they will be chased off. This is known as guarding behavior. The male sticks to the female like glue until they have mated, or it is made clear there will be no romantic entanglement.

Food

Hermit crabs have small stomachs and are rarely gluttonous. Some hermit crabs may hoard food, though. This is a sign of dominance. This means that squabbles can break out at the feeding dish.

Prevent hermit crabs from storing food in their shell, favored hiding places, or under the substrate. They will likely forget about their treasure. This means the food will quickly rot. This becomes a bacterial hazard, attracting mold and other health concerns.

If your hermit crabs have a complicated relationship with food, hand feed them individually. This will ensure that all hermit crabs enjoy sufficient nourishment. It can also be a great way to bond with your hermit crabs and reduce aggression based on anxiety.

hermit crab fighting behavior

Identifying a Hermit Crab Fight

As discussed, there are different styles of hermit crab fights. Sometimes, they are just amusing themselves and having fun. On other occasions, they may even be mating. This is rare in captivity, though.

Learn to spot the difference between fighting, playing, and mating in hermit crabs. If your pets are fighting, they should be separated before one of them is hurt. Mating in captivity should never be interrupted – it is a minor miracle. Playfighting is harmless fun.

Watch your crabs for a few seconds. Observe and review the table below for what you consider the closest description of what is unfolding. This will help you assess if your hermit crabs are mating, fighting, or playing.

Chirping and croaking:Fighting, or at least planning to
Climbing over each other:Playing
Dragging another crab out of its shell:Fighting – break up immediately
Guarding another occupied shell:Male wants to mate, is fending off rivals
Male gently rocking the shell of a female:Attempting to coax mating
Pushing and shoving each other:Playing, but can escalate to fighting
Strongly rapping on the shell of another crab:Challenging to a fight
Swiping eyes, claws or abdomen with pincers:Fighting – break up immediately
Wrestling and pushing antennas:Playing

As you’ll see, when hermit crab conflict escalates to fighting, they should be separated. Temporarily rehome both hermit crabs in a separate dark, private enclosure to cool off. Be careful when picking them up. Lift the shell and keep your hands away from pincers.

Do Hermit Crabs Fight to the Death?

Most hermit crabs will not attempt to hurt each other. For example, in a conflict over shells, victory is rarely decided by whoever is the last hermit crab standing. It’s more like a TKO.  As per Animal Behavior, the winner of shell disputes is usually the hermit crab with the most energy.

In shell conflict, one of the hermit crabs will give up eventually. This could be the aggressor, with the resident relinquishing their shelter and agreeing to trade. Alternatively, the resident may stand firm until the aggressor grows tired or bored and walks away.

Alas, there are always exceptions to every rule. A particularly angry, aggressive, or desperate hermit crab may take things too far. This is why fights should be broken up. You cannot watch your hermit crabs 24/7 but do all you can to keep them safe.

If you have two hermit crabs that cannot get along, separate them in different homes. Do not keep either of them alone. That will just make the hermit crab even more antisocial. Divide your tank occupants in half, housing friendly crabs with each pugilist.

Why Do Hermit Crabs Eat Each Other?

As per Reviews in Fisheries Science & Aquaculture, acts of cannibalism can be common in decapod crustaceans. Hermit crabs are typically the exception to this rule. Hermit crabs rarely hunt and eat live prey, with the possible exception of insects.

A dead hermit crab may be eaten by its tankmates, though. The first explanation for this is instinct. Wild hermit crabs are scavengers and will survive by eating anything they can find.

This frequently includes dead animal carcasses, including those of conspecifics. If a hermit crab eats a friend, it knows it will consume fat and calcium. This can be dangerous, though. The hungry crabs may also ingest toxins if they killed the animal in question.

Cannibalism in hermit crabs is also a defense mechanism. The hermit crabs can smell the corpse, which suggests that predators can scent it too. This can attract invaders and reveal the presence of live crabs. Eating their dead hides and removes evidence of the living.

If you keep multiple hermit crabs together – which you should – they will occasionally attack each other. While hermit crabs enjoy living in groups, they squabble and play fight. Only be concerned if the conflict turns vicious. In most instances, hermit crabs resolve differences among themselves.