Marine Invertebrates

Hermit crab


  • Scientific name: Panguroideos (Paguroidea)
  • Common name: Hermit crab
  • Aquarium size: 150 liters
  • Temperament: Calm
  • Temperature: 24ºC to 26ºC
  • pH: 7 to 8.9
  • Diet: Omnivore
  • Length: Between 20mm and 10 centimeters


The hermit crab or paguros, are crustaceans of the pagouridea or paguroidea family.

There are about
500 different species of hermit crabs throughout the world, the majority being water crabs, although there are some terrestrial varieties.

What has made these crabs famous, in addition to Disney movies, is the special relationship they have with the shells of other dead mollusks.

need a shell to cover their abdomen that is much softer than the rest of the crabs.

The shells change them as they grow and need more space.


They are crabs that lack protection for their abdomen, so they seek to protect themselves using abandoned shells of other dead mollusks, this behavior is called thanatochresis .

The hermit crab’s abdomen curls to fit the chosen shell, and uses its legs and claws to block the entrance to its «home.»

Despite having an unprotected abdomen, the rest of its body
is protected by a rigid exoskeleton, so that the part of the body that is outside the shell, if it has protection from predators.

It has ten legs, the first two being pincer-shaped, which are used to capture and manipulate its prey.

As a curiosity,
the right claw is larger than the left, as with the fiddler crab .

The other four front legs are used to move, while the other four legs are hidden inside the shell, because it uses them precisely to hold it.

In its head we can find two eyes at the end of appendages, as well as
two antenna-shaped organs called antenular flagella, which serve to perceive everything that happens around it.


As I have mentioned before, we are talking about a genus of crustaceans, with more than 500 different species.

There are a
large number of colors associated with hermit crabs, although the most common are red and brown, although they can have grayish, orange tones, and some are bright red.

The area where they live and their environment greatly influences their coloration.

Shell development and change

The hermit crab begins to look for its first shell to protect its body, when it has already developed its four antennae and two claws, while this growth process lasts, it frequently changes its skin, until it reaches the magalopic stage.

In order to change shells, the hermit crab has to break its old shell, to do so it needs to increase its body.
It does this by absorbing water to increase its weight by 70%.

Once their old shell is broken, they look for one that is large enough to serve them and allow room to grow.

Distribution and habitat

We can find hermit crabs almost everywhere on the planet, as long as the temperature conditions are right, as they prefer tropical habitats.
The continents where they are most easily found are the American and European.

In Europe they can be found
in the Mediterranean Sea and the Baltic Sea. In the American continent their populations are distributed from Alaska to Mexico.

In Asia they can also be found
from the Bering Strait to Japan.

They like to live near the coast, they do not care if the bottom is rocky, with reefs or sand, although their favorite places to live are under the rocks.

Aquarium conditions

If you decide to take care of hermit crabs, you should know that they like to be in community, and you should put three or four specimens in the aquarium.

Depending on the species, the size of the aquarium can vary, but you can have three or four large specimens in an aquarium of about 150 liters.

They need a sandy substrate, in which they can hide and move.

We must also provide them with the possibility of getting out of the water, with rocks, a sandy area out of the water, logs, etc.

Remember that, although they are marine animals, they like to get out of the water and walk along the beach.

The water must have a temperature between 24ºC and 26ºC, with a pH between 7 and 8.9.


They are an omnivorous species, they will eat practically everything. In nature they eat other smaller crustaceans, such as snails , mussels or prawns, also worms, remains of a dead animal that are found and of course, plant remains.

In an aquarium they will adapt to eating pieces of fish, mussels or prawns, we can also provide them with vegetables and pieces of fruit.

Behavior and compatibility

They are calm animals by nature, except when they need to change shells.

If there are several crabs and there are not enough shells for all of them, they will fight each other.

In addition to using shells that are not theirs for protection, they also
often develop a relationship of convenience with anemones , which can latch onto their shells.

Interestingly, even if the crab changes shells, the anemone will follow the crab wherever it goes.

While the anemone keeps predators away from the crab,
the anemone consumes the food debris left by the crab.


Hermit crabs are oviparous, they reproduce by eggs twice a year.

The female usually carries her eggs under the abdomen, until they are fertilized by the male.

Once fertilized, the female releases them into the sea, where they hatch and become part of the zooplankton.

Fortunately they
lay hundreds of eggs that will grow into adults.

Hermit crab photos

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