Hermit crabs aren’t happy when kept alone. Ideally, they should be kept in groups of 3 or more, depending on space, but a pair can work. When choosing companions for your hermit, you may need to make size-based choices. Many owners believe that you need to keep hermits of identical sizes, while others claim that it doesn’t matter.
Hermit crabs can live together regardless of their size. While it’s ideal if all hermit crabs are of a similar size, big hermies can live with small hermies. They’re no more likely to fight or get into altercations. The only risk is improper care or habitat conditions, which can lead to smaller hermies getting bullied.
If your hermit crabs have enough space, food, and basic resources, they’ll live together in harmony. If fights do happen, upsizing or adding enriching features to the tank should resolve any aggression issues. If taking this action doesn’t resolve the problem, you may need to separate the hermits until you can narrow down the problem.
Do Big Hermit Crabs Get Along with Small Ones?
Big hermit crabs can get along with small hermit crabs. They need time to get to know each other. That’s because hermit crabs are good at building relationships.
According to Ethology, they may start to recognize other hermit crabs after a single 30-minute exposure to them. When you introduce a new hermit crab, whether large or small, one is likely to approach the other for a friendly antenna sparring match.
This may look a little worrying at first, but it is crucial to forming social harmony. Antenna sparring is a way for hermit crabs to understand where a newcomer fits in their existing social hierarchy. It shouldn’t result in aggression. Antenna sparring may also be accompanied by leg sparring.
Hermit crabs have complex social behaviors and hierarchies in the wild, and this translates into domestic settings. A group of hermit crabs that are kept as pets will have their own social structure and hierarchy. In a situation where large and small hermit crabs live together, the most important factor is which hermit is new to the group.
New hermit crabs are often treated, accurately, as outsiders. The other hermit crabs will approach the new hermie with curiosity and a degree of stand-offish behavior. If any conflict arises, it will arise at this time, but it has little to do with the size of each hermit. Size only determines who is going to win the fight.
If aggression comes, it will be in the form of cheliped sparring. As long as they are grasping each other’s claws, this is most likely a harmless way to assert dominance.
However, if you see your hermits trying to sever limbs, antenna, or eye stalks with their chelipeds, it is time to separate them. These actions are undoubtedly aggressive and can cause injury or death.
Will Big Hermit Crabs Kill Small Ones?
While acts of serious aggression are possible, it’s not common for hermit crabs to kill each other in fits of aggression.
Of course, larger hermit crabs have a higher chance of killing smaller hermit crabs by accident during a fight. Nonetheless, well-kept, happy hermit crabs shouldn’t feel overly aggressive or fight. They might spar as a natural part of communication from time to time, but no injury should result.
However, there are some instances in which hermit crabs of any size can kill each other. The most common situation in which a hermit will kill another is during an attempted shell theft. There has been some scientific debate about whether attempted shell theft is an act of negotiation or aggression.
Some argue that this is a matter of negotiation. According to Animal Behaviour, though, the intensity and length of fights increased in tandem with potential gain.
In short, hermit crabs in dire need of a larger shell or those trying to get a particularly attractive shell were more likely to be severely aggressive when trying to steal a shell. In unsupervised situations, this can lead to injury and death.
During an attempted shell theft, death most often occurs when a larger, stronger hermie tries to pull a weaker or smaller hermit crab from a desirable shell.
This is, in part, due to the immense struggle the incumbent hermit crab will put up. Forceful removal of a hermit crab from its shell is likely to lead to the hermie splitting in the middle, causing death.
How Big Can Hermit Crabs Get?
There are more than 1,000 hermit crab species globally, the largest of which is the coconut crab.
This gigantic species can have a leg span of 3 feet when mature, but of course, these are not a pet species. In the United States, the main domestic species of hermit crabs are coenobita clypeatus and coenobita compressus.
The coenobita clypeatus, or Caribbean hermit crab, can grow up to 6 inches in length when fully grown. Meanwhile, the coenobita compressus or Ecuadorian hermit crab is much smaller at 12 mm. to 1 inch in size. While different hermit crab species can live together, it is not recommended. Each species has slightly different ideal conditions.
This, combined with the vast difference in the average size of these species, means that housing them together is far more likely to result in aggression or bullying. One is not more likely to cause fights than the other, but any aggression can immediately turn deadly because of the size difference.
Of course, the smaller Ecuadorian hermit crabs are likely to bear the brunt of any bullying in this situation. They’re better kept in single-species habitats where their specific needs can be met.
Can You Put Big and Small Hermit Crabs Together?
You can put big and small hermit crabs together, but you have to make sure that their habitat is suitable. Keeping any group of hermit crabs happy and preventing them from fighting comes down to this.
It’s a matter of ensuring that they have a habitat that meets all of their needs:
To be happy and relaxed, hermit crabs need:
- Ample substrate of the right kind
- Things to climb
- Spaces to hide
- A habitat temperature of roughly 80 F
- Humidity of 75 – 80%
- Ample food
Tank Size for Big and Small Hermit Crabs
It is recommended that you have a 10-gallon tank minimum. However, a small hermit crab of 1 inch across the shell needs a minimum of 2 gallons of space to itself.
Therefore, if you have three small hermit crabs, you will find that a 10-gallon tank will quickly become cramped as they grow. If you have large hermit crabs along with small ones, you will need a larger tank.
Giant breeds can require 60- to 90-gallon tanks.
Substrate for Mixed Species Hermit Crabs
Furthermore, you will need substrate 3 times as deep as the size of your largest hermit crab. Hermit crabs love to dig. This behavior is integral to large parts of a hermit crab’s life and is even how it protects itself during molting.
Ecology shows that hermit crabs do not like muddy, silty, or overly wet substrate. Instead, you should give them a substrate that is 5 parts sand to 1 part coco fiber.
Toys for Small and Big Hermit Crabs
As well as substrate to dig in, hermit crabs need places to hide and enriching toys. Hiding places allow hermit crabs to de-stress.
Hermit crabs will hide inside their shells, of course, but you should also provide shaded or enclosed spaces for them to hide in when feeling agitated.
Likewise, toys, ropes, rocks, and netting for climbing will stimulate your crabs and stop them from getting bored.
Food for Different Sized Hermit Crabs
You need a plentiful supply of the right kinds of food for your hermit crabs.
If your hermits are stressed or resources like hiding spots, toys, and food are scarce, fights become more common. Hermit crabs are omnivorous scavengers, too, so don’t be afraid to offer a variety of food to help ensure happiness.
Can Different Sized Hermit Crabs Live Together?
Differently sized hermit crabs should co-exist peacefully. That is, so long as you’ve ensured the habitat is:
- Of the right size
- Has enough of the right type of substrate
- Outfitted with plenty of toys and hiding places
- Contains plentiful food of the right kind
However, you may find that your large hermit crabs are still bullying smaller tank mates, or any of the hermits are fighting regularly. If so, two further issues could be at work.
If the behavioral issues revolve around shells (or, more specifically, hermits attempting to take already inhabited shells), then the issue could be a lack of suitable shells.
Hermit crabs molt as a part of their growing process. They will seek out a new, bigger shell after molting. While they may stick with their old shell for a short while as they grow, it will start to become uncomfortable.
This discomfort can become a motivating factor in hermit crabs showing aggression and trying to de-shell tank mates. Finding out whether this is the case is relatively easy.
Isolate the aggressive hermit crab and provide it with a range of shells to choose from. If its shell is too small, it will seek out a new one. Providing a wider range of shells in the main tank should prevent further fights.
Let’s assume your hermits have enough shells to choose from, as well as enough food, substrate, climbing toys, hiding places, and space. In this case, aggression and bullying are most likely behavioral problems.
There are times when bigger, stronger hermit crabs bully smaller tank mates to get their way. If one hermit crab is pushing the others around, you will soon see a pattern.
Stopping Big Hermit Crabs from Attacking Small Hermit Crabs
Signs of aggression in hermit crabs can take many forms. For example, hermit crabs may croak or chirp when agitated.
This can be a sign of minor irritation or active aggression but may also be a reaction to being pushed around. If you hear croaking or chirping, it’s most likely a sign that there is a source of tension in your hermit crab tank.
Likewise, cheliped clashes or sparring can be aggressive acts if the hermit crabs try to sever limbs or cause other bodily harm. In some cases, widespread aggression can be caused by a lack of protein.
However, when a singular hermit crab is behaving badly and pushing smaller hermit crabs despite having everything it needs, you can address the issue by isolating that hermie.
The best idea is isolating an aggressive hermit crab that is bullying its tank mates. You can provide it with somewhere dark and private while you assess the tank.
Once you have isolated that hermit crab, you should try replacing substrate, switching up toys and hiding places, and offering new shells. If stress or boredom were to blame for its behavior, the hermit crab should be less aggressive after reintroducing it to its tank mates.
Hermit crabs can live together, no matter their size. Large with small, medium with large, and small with any size can all work. It merely depends on how well the entire tank is set up.
The size differences won’t cause fights, but an unsuitable habitat might. In this case, the size difference determines who will win the fight and who might get hurt.