Creature of the Month: Hermit Crab, Dardanus species

Hermit crabs scuttle about the sea-floor using someone else’s
shell for a home. They always use empty shells and never
kill the original occupant.

When the crab becomes to large for its shell, it looks for
another. When it finds a likely looking one it will
try it on. If the shell doesn’t fit, or is too heavy,
the crab returns to its old shell and continues it search.

Where there is a large population of hermit crabs and
a shortage of shells, the crab will accept a sub-standard
home: maybe a cracked or uncomfortable shell. But in good
conditions it will be very particular about the new shell
it chooses. Two hermit crabs will fight for the possession
of an empty shell, or even a shell inhabited by one of the
combitants.

Some of the Dardanas species of Hermit crab stick sea
anemones on their shells. This camoflauges the crab and
the stinging cells of the anemone protects the crab from
predators such as octopus.

The anemone also benefits from the arrangement. It becomes
effortlessly mobile and shares the crab’s meals.

Dardanas species are nocturnal with dark-adapted eyes.
Look out for them on night-dives in the Indian and
Pacific oceans.