Think Tank's hermit crab exhibit and the associated panel "Shell Seekers" provide visitors with an opportunity to explore the definition of tools and the evidence of thinking during tool use.
Distribution and Habitat
Land hermit crabs of many different species are found in tropical
areas of the Indo-region, the western Atlantic, and the western
Caribbean. They live close to the shoreline and must have
access to land and water. There are also entirely aquatic
species of hermit crabs.
Physical Characteristics
The front half of a hermit crab is covered with a hard exoskeleton
(hard outer skin). The long abdomen has a softer exoskeleton,
that can adjust to fit into a spiraled snail shell. A crab
presses its abdomen against the shell's inner wall by contracting
its longitudinal muscles. The large left claw is used for
defense, for holding onto tree limbs, and for balance. The
smaller right claw and the next pair of appendages are used
for collecting and passing food and water to the mouth. Hermit
crabs have stalked eyes with acute vision and two pairs of
antennae. The longer pair of antennae is used for feeling,
the shorter for smelling and tasting.
Molting
As a hermit crab grows, it molts, shedding its exoskeleton
and creating a new, larger one. A crab builds up enough
water pressure in its body to split the old skin. A
crab may eat its molted skin, possibly for its calcium,
vitamins, and minerals.
Shell Selection
Hermit crabs use shells for protection from predators and
dehydration. A hermit crab has a ranked hierarchy of fixed
motor patterns that it goes through when choosing a new shell.
Image and intention may be part of the pattern, but that does
not mean thinking is occurring. The steps are always the same,
in the same order, and show no flexibility.
Diet
In the wild, hermit crabs are omnivorous scavengers, meaning
they eat whatever they can find. At the Zoo, they are fed
fish food, crab food, and various fruits and vegetables.
Life Span
Land hermit crabs live about ten years.
Reproduction
Hermit crabs mate in saltwater. Both males and females partially
emerge from their shells to mate. After the eggs hatch, the
larvae go through several aquatic life stages and molts. When
they reach adulthood, the crabs migrate to begin their terrestrial
life.
Husbandry
Land hermit crabs are good climbers and should be kept in
a covered container. They need a good supply of empty shells
to try on after molting. Hermit crabs also need high humidity
and should be able to go into water. At the Zoo, petroleum
jelly is used around the edges of the tank to keep ants out.
Hermit crabs are not aggressive, but the large, purple claw
can give a nasty pinch — so zookeepers handle them with
care!
