Hermit Crab Interesting Facts

One of the most distinguishing characteristics of the hermit crab includes its use of the shells of other creatures for protection. Some hermit crabs live in sponges from which they move around the ocean floor. Hermit crabs live in a variety of marine areas including reefs and tide pools. Careful observation of tide pools may provide a glimpse into the interesting lives of these little creatures.

  1. Description

    • Hermit crabs sport jointed limbs and segmented body parts consisting of a head, a middle body section called the thorax and an abdomen, the softest part of the crab. The crabs have two pairs of antenna, mouth parts called mandibles that crush prey, and a hard external skeleton. Hermit crabs use five pairs of legs with one pair modified into claws, useful to catch and eat prey.

    Behavior

    • The crab protects its abdomen by finding empty snail shells where its curved abdomen fits perfectly into the empty space. The crab uses hook-like limbs to anchor its body to the shell. Once the crab outgrows the shell, it starts looking for a bigger one. Sometimes the crab encourages another crabs to leave its shell by pulling the other crab out. Other times, smaller crabs wait near an occupied shell for a larger crab to move out so it can move in. When the crab feels ready to occupy the new space, it releases its anchors from the old shell and slips into the new shell. If the crab decides the new shell won't work once it has moved part way in, it scurries back to the old shell before another crab can move in.

    Species

    • More than 500 species of hermit crabs exist in the world. Some hermit crabs, such as the Calcinus verilli, live in one area only. The Calcinus verilli crab lives in marine areas near Bermuda in the Caribbean. Six different species of hermit crabs live in Hawaii, including the left-handed tide pool hermit crab, Calcinus laevimanus. This crab uses its large left claw as a door to give its shell added protection.

    Food

    • Hermit crabs eat plant material, such as algae, and small marine animals scavenged off the ocean floor. In turn, the crabs get preyed upon by larger hermit crabs, octopus and reef fish who can crush the shells with the hermit crab inside.

    Conservation

    • Since hermit crabs rely on the shells available in the reefs or tide pools, scientists at the Waikiki Aquarium at the University of Hawaii suggest avoiding collection of the shells found in these areas. Without knowing it, many people pick up shells with crabs living inside, causing the crab to die without food and water. Leaving the shells in place, especially larger, rare shells, helps the crabs find the homes they need to protect themselves while also maintaining their population.