How Does a Hermit Crab Find Its Shell?

Hermit Crab Shells

Hermit crabs have soft abdomens. A hermit crab's abdomen needs protection, and this protection comes from the hermit crab's shell. But a hermit crab isn't able to grow its own shell. It usually finds an empty seashell and moves into it after rolling it around to empty the shell of any debris.
Seashells offer great protection, and also help the gills retain moisture, which is essential to the hermit crab. Hermit crabs will also use bottle caps, miniature bottles, or other trash as shells if they can't find an appropriate seashell. These artificial shells aren't as effective, especially in conserving the hermit crab's moisture. The first shell a juvenile hermit crab chooses actually determines the shape its abdomen will take.

Hermit crabs periodically outgrown their shells. They are always looking for a perfect new shell, even if they haven't outgrown the current one. The perfect size shell is one that the hermit crab can close itself up in, with its large claw blocking the opening.

The lining of the seashell is also important. The hermit crab will feel the lining of a shell before it moves in, searching for jagged spots that might injure it. Hermit crabs tend to prefer shells with mother-of-pearl lining because mother-of-pearl is thick and smooth.

Although it's natural for the owner of a hermit crab to want to see her crab change shells, hermit crabs are at their most vulnerable during a shell change. For this reason, they usually change shells while they are alone.
The owner of a pet hermit crab should have at least five new possible shells available for his crab at all times. The shells shouldn't have any holes or cracks. The shells should be the same size or a little larger than the hermit crab's current shell. Shells that look the same size on the outside can have different amounts of space inside. It's best to avoid painted shells. The paint can chip off and cause health problems for the crab.
Most hermit crabs prefer seashells with round openings. However, the Ecuadorian hermit crab--with its wider, flatter head and body--prefers shells with slit-shaped openings.
Hermit crabs can get into fights over shells, so it's important to increase the number of available shells if you have more than one pet crab.
Any shells offered to pet hermit crabs should be clean. Boil the shells in water for five minutes, then let them cool before giving them to the crabs.