Hermit crabs live in large colonies of up to 100 in the wild. Captive hermit crabs should live in groups of three or more, depending on the available space, but a pair can work.
Hermit crabs of the same species can live together, regardless of size. While it’s ideal if they’re similar, big hermit crabs can live with small hermit crabs, as there’s no evidence that they’re more likely to fight.
The only risk is suboptimal tank conditions that lead to smaller hermit crabs getting bullied. If your hermit crabs have enough space, food, and basic resources, they’ll live together in harmony.
If fights happen, upsizing and adding new features to the tank will resolve most issues.
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 because hermit crabs are good at building relationships.
According to Ethology, hermit crabs will recognize others after a 30-minute exposure. When you introduce a new hermit crab, whether large or small, one will likely approach the other for a friendly antenna sparring match.
At first, this may look worrying, but it’s crucial to social harmony. Antenna sparring is a way for hermit crabs to understand where a newcomer fits in their social hierarchy, and 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, which also applies in domestic settings. A group of hermit crabs kept as pets will have a social structure and hierarchy. When large and small hermit crabs live together, the most important factor is which hermit is new to the group.
New hermit crabs are initially treated as outsiders. The other hermit crabs will approach the new hermit crab with curiosity and a degree of stand-offish behavior. If any conflict arises, it’ll arise at this time, but it has little to do with the size of each hermit. Size only determines who is going to win a fight.
If aggression arises, it’ll be in the form of cheliped sparring. As long as they grasp each other’s claws, this is most likely a harmless way to assert dominance.
However, if you see your hermits attempting to sever limbs, antennas, or eye stalks with their chelipeds, it’s 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 aggression are possible, it’s uncommon for hermit crabs to kill each other.
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 instances in which hermit crabs of any size can kill each other. The most common situation where 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, the intensity and length of fights increased in tandem with potential gain. In short, hermit crabs in dire need of a larger or better shell were more likely to be aggressive when trying to steal a shell.
Death commonly occurs during an attempted shell theft when a larger, stronger hermit crab tries to pull a weaker or smaller hermit crab from a desirable shell.
This is partly due to the immense struggle the incumbent hermit crab will put up. Forceful removal of a hermit crab from its shell will likely lead to it 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 they’re not a pet species. The main domestic species of hermit crabs in the U.S. are coenobita clypeatus and coenobita compressus.
The coenobita clypeatus, or Caribbean hermit crab, can grow up to 6 inches long. Meanwhile, the coenobita compressus (Ecuadorian hermit crab) is much smaller at 12 to 25.4 mm.
While different hermit crab species can live together, it’s not recommended, as each species requires slightly different living conditions.
This, combined with the vast difference in the average size of these species, means that housing them together is more likely to result in aggression or bullying. One isn’t 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 ensure their tank is suitable.
To be happy and relaxed, hermit crabs need:
- Sufficient space
- Ample substrate, such as sand
- Things to climb
- Spaces to hide
- A temperature of 80 F
- 80% humidity
- Ample food
- 12 hours of light and 12 hours of dark
It’s 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 for itself.
Therefore, if you have several small hermit crabs, you’ll find that a 10-gallon tank will soon become cramped as they grow.
You’ll need a bigger tank if you combine small and large hermit crabs.
Furthermore, you’ll need substrate three times as deep as the size of your largest hermit crab.
Hermit crabs love to dig, as 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 dislike muddy, silty, or overly wet substrate. Instead, provide a substrate with five parts sand to one part coco fiber.
Hermit crabs need hiding places and toys, as these allow hermit crabs to de-stress.
Hermit crabs will hide inside their shells, but you should provide shaded or enclosed spaces to hide in when they feel agitated.
Likewise, toys, ropes, rocks, and netting for climbing will prevent hermit crabs from getting bored.
Provide a plentiful supply of the right food for hermit crabs.
If your hermit crabs are stressed or resources like hiding spots, toys, and food are scarce, fights become more common. Hermit crabs are omnivorous scavengers, so they need food diversity.
Can Different-Sized Hermit Crabs Live Together?
Differently sized hermit crabs should co-exist peacefully. However, you may find that large hermit crabs are still bullying smaller tank mates. If so, two further issues could be responsible:
If the behavioral issues revolve around shells (or, more specifically, hermit crabs attempting to take already inhabited shells), the issue could be a lack of suitable shells.
Hermit crabs molt as a part of their growing process and will seek a new, bigger shell after molting. While they may stick with their old shell for a short while as they grow, it’ll become uncomfortable.
This discomfort can motivate hermit crabs to show aggression and 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. If its shell is too small, it’ll seek a new shell. Providing a wider range of shells in the main tank should prevent further fights.
Let’s assume the hermit crabs have enough shells, food, substrate, climbing toys, hiding places, and space. In this case, aggression and bullying are most likely behavioral problems.
Sometimes, bigger, stronger hermit crabs bully smaller tank mates to get their way. You’ll soon see a pattern if one hermit crab pushes the others around.
Stopping Big Hermit Crabs from Attacking Small Hermit Crabs
If you hear croaking or chirping, it’s most likely a sign that there’s a source of tension.
When one hermit crab is behaving badly and pushing smaller hermit crabs despite having everything it needs, you can address the issue by isolating them.
Once you have isolated that hermit crab, try replacing the 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 being reintroduced to its tank mates.
Hermit crabs can live together, no matter their size. Large with small, medium with large, and medium with small can all work. It depends on how well the tank is set up for hermit crabs’ needs.
The size difference between two hermit crabs won’t cause fights, but mixing different species will.