Hermit Crab Changing Seashells
First it is probably best to explain that hermit crabs do not make the seashells that they live in. Due to the softness of a hermit crabs abdomen, they have no choice but to try and find suitable protection. Because of their environment this usually ends up being an empty seashell. A seashell provides excellent protection and also helps to retain moisture to a hermit crabs gills. If a crab is able to find the perfect seashell it would ultimately be able to completely close itself up in the shell with it's large claw totally blocking the opening on the seashell.
The search for a perfect seashell continues throughout a hermits life. It is always in search of the perfect fitting shell or it has outgrown the one it is in. We have found that when new shells are introduced most hermit crabs check them out and will change with in a 24-48 hour period.
Having a good supply of changing seashells for your crab is extremely important to maintaining a healthy crab. If a hermit crab does not have a new shell to move into and has out grown the one they are in, they will find some other hollow cover to substitute. While it might be nice to see a hermit crab walking around with a soda cap on their back, they will not survive for long since a cap cannot maintain the moisture a hermit crab needs for survival.
A hermit crab will move into a wide variety of seashells. The key is to pick a seashell that has a slightly larger opening then the one they are in now. Some seashells are very large in size, however have very small openings on them. An optimum seashell would be one with an opening just about the size of the hermit crabs large claw.