Last Updated on October 21, 2023 by Joanne Harper
Usually, hermit crabs have separate shells. A shell is pivotal to hermit crabs’ survival, protecting them from dangerous predators (like birds) and drying out in the sun’s UV rays.
Occasionally, two hermit crabs will live in the same shell. This will only be a short-term housing arrangement because the more dominant hermit crab will eventually claim the shell and live alone.
When two hermit crabs enter a shell, it’s usually by accident, not design. A hermit crab could enter the shell when the occupant is molting, believing the other hermit crab is deceased.
Two juvenile hermit crabs may temporarily share a large and robust shell until they grow. This heavy, cumbersome shell would be too much for one hermit crab to transport.
Can Two Hermit Crabs Live in One Shell?
Two hermit crabs can share a shell, but it’s uncommon.
The ideal shell for a hermit crab will fit snugly around its body, leaving just enough space to retreat inside. This shell won’t leave space for a second hermit crab.
Despite this, hermit crabs have occasionally been observed sharing shells. As independent animals, why would hermit crabs share shells?
Thought The Shell Was Empty
The most common reason two hermit crabs share a single shell is mistaking molting for death. This can happen in the wild or captivity, but it’s more commonplace in the wild.
When hermit crabs undertake a complete molt, the process can resemble death.
The hermit crab will become entirely still, and the exoskeleton it sheds will start to smell. According to Ecology and Evolution, this releases a scent that attracts other hermit crabs.
If hermit crabs smell what they believe to be a dead hermit crab, they assume a shell is vacant.
As a conspecific previously used this shell, it’ll be considered suitable for habitation. A new hermit crab may move into the shell, not realizing that a molting incumbent remains inside.
Both hermit crabs will need to be small for this arrangement to work. Even if so, it’s not a sustainable living arrangement. Eventually, one of the hermit crabs will need to leave.
The new residents may realize their mistake and seek different shells. Alternatively, the molting hermit crab may decide the shell no longer meets its needs and seek an upgrade.
It’s likelier that the two hermit crabs will fight for the right to retain the shell.
Hermit crabs are omnivorous and display cannibalistic tendencies. Consequently, a larger and more aggressive hermit crab may eat a smaller rival.
In this instance, the molting hermit crab is at the most risk.
Even if the molt has concluded, it takes a couple of weeks for a hermit crab’s new exoskeleton to reach full strength. This makes the molting hermit crab vulnerable to attack.
Lack of Individual Shells
Occasionally, two small hermit crabs share a shell because they can’t find individual options that meet their needs. Going without a shell isn’t an option, as it leaves hermit crabs completely vulnerable.
According to the journal Crustaceana, shell-sharing is more common in the wild. As the population of hermit crabs grows, suitable shells can become scarce.
Captive hermit crabs shouldn’t feel the need to share shells. Spare shells are easily obtained by foraging on the beach and sanitizing what you find or purchasing shells at an exotic pet store.
Always keep spare shells in the tank, on the periphery of eating and recreational areas.
Occasionally, two hermit crabs may share a shell to get more protection from predators. This will only arise among young hermit crabs looking to improve their chances of survival.
If the shell is oversized, sharing may be considered a worthy option in the short term.
A large, heavy shell offers superior protection to a smaller, damaged alternative. According to the Journal of Zoology, most hermit crabs prefer a heavier shell that offers enhanced fortification.
The combined strength of 2 hermit crabs makes a heavy shell easier to negotiate. A cumbersome burden can prevent the hermit crabs from engaging in other activities, like exploring and climbing.
As a consequence, the arrangement won’t last long. Young hermit crabs grow rapidly, undergoing several molts and increases in mass in the first 18 months of life.
Unless the shell is large, it won’t accommodate a pair of hermit crabs.
What Should I Do if Two of My Hermit Crabs Are Sharing a Shell?
Don’t ignore the arrangement if you notice 2 captive hermit crabs sharing a shell. While you shouldn’t force a hermit crab out of its shell, do your utmost to encourage evacuation.
The easiest way to achieve this is with appealing shell alternatives.
Place a range of new shells in the hermit crab’s habitat, and the residents will line up according to size and start trading shells until everybody has the ideal shelter.
Fights may break out over preferred shells, but for the most part, these negotiations will be amicable.
If the hermit crabs are wrestling with their antennae, leave them to resolve the conflict. If they start pinching each other, separate them until they calm down.
You may also find that two hermit crabs get trapped in a single shell, as the evacuation point is too small. Try submerging the hermit crabs in water for a few minutes.
You may notice that neither hermit crab wants to be the first to leave the shared shell, which involves conceding ownership to a rival. Tempt the hermit crabs out with food.
Land hermit crabs are unlikely to share a shell. Mollusk shells are popular among hermit crabs, but only once vacated. It’s rare for a hermit crab to evict another species from a shell.
Marine hermit crabs may share their shells with sea anemones. The sea anemone won’t hide inside the shell of a hermit crab but will dwell on the back of its shell or the chelipeds.
Zoological Science explains that hermit crabs and sea anemones have a symbiotic relationship. This means that both parties benefit from the arrangement.
Sea anemones deter aquatic predators of the hermit crab, most notably fish and true crabs. Sea anemones can access food that wouldn’t otherwise be available to them.
If 2 crabs live in the same shell, it’s due to necessity and isn’t a lifestyle choice.