Today’s Wonder of the Day was inspired by Ferd. Ferd Wonders, “What is a hermit crab?” Thanks for WONDERing with us, Ferd!

Are you feeling crabby today? If so, cheer up! We're going to learn about some interesting creatures that make great pets at home or at school.

Hermit crabs are crustaceans. Crustaceans are a class of creatures with segmented bodies and exoskeletons (external skeletons) that includes lobsters, shrimp, and crabs.

Hermit crabs can live either on land or in water. They're not true crabs, though.

In fact, they're more like squat lobsters than true crabs. True crabs have abdomens protected by hard shells.

Hermit crabs have soft, exposed abdomens. This leaves them vulnerable to predators.

To protect themselves, hermit crabs search for abandoned shells — usually sea snail shells. When they find one that fits, they tuck themselves inside it for protection and carry it with them wherever they go.

This habit of living in a borrowed shell gave rise to the hermit crab's name. Since hermit crabs often retreat completely into their borrowed shells for protection, some people think they act like hermits.

Hermits are people who live alone and do not interact often with others. Hermit crabs aren't really hermits, though.

They tend to be quite social animals that enjoy living in groups. In the wild, they can often be found in large groups of 100 or more.

As hermit crabs grow, they often outgrow their borrowed shell. When this happens, they have to “shop" for a new one.

Hermit crabs can be very picky about the shell they choose. They want a shell that they can fit into completely in case they need to hide for protection.

Sometimes hermit crabs that live together help each other find new shells. When a new, large shell becomes available, hermit crabs have been known to form a line by it from largest to smallest.

The largest crab moves into the new shell. The next largest crab moves into the shell just vacated by the last crab and so on.

Hermit crabs sometimes like to “decorate" their shells. To help camouflage themselves and add an extra layer of protection, hermit crabs sometimes carry sea anemones on their shells.

Sea anemones are poisonous, so other creatures will usually avoid them and leave the hermit crabs alone.

Many people — and a lot of schools — keep hermit crabs as pets in aquariums. Hermit crabs are great for aquariums because they eat algae and debris to help keep the tank clean.

Most hermit crabs are fairly small. However, one land-dwelling hermit crab can get quite large. The coconut crab can grow to be up to three feet long and weigh nine pounds!

The coconut crab is unique in another way, too. When it outgrows the largest shell it can find, it grows a shell of its own.

Wonder What's Next?

Tomorrow’s exotic Wonder of the Day will help keep you on track!