Hermit crabs do not make their own shell, they have to find discarded shells from snails (gastropods). Shells provide protection from the elements and predators, and retains water to keep their soft body and gills moist. A hermit crab cannot survive without a shell.
Not just any shell will do and choosing the right shell can be confusing and frustrating for many crab owners. The majority of the information you’ll find here is specific to Coenobita Clypeatus (commonly called the purple pincher/PP, soldier crab or Caribbean hermit crab) which is the most common species available in the United States.
The purple pincher hermit crab prefers shells with round openings such as turbo or turban shells. The shells of land snails are rarely used, likely due to how thin they are in comparison to sea snails. Ecuadorian hermit crabs (which can also be purchased in the US) may prefer D-shaped openings but will also inhabit shells with round openings. Some of the more common types of shells chosen by hermit crabs, and readily available for purchase, are Argyrostoma, Setosus, Pica, Petholatus, Jade, Bruneus, Mexican turbo, Babylonia, Murex, whelk, and Nerite.
All shells need to be inspected for any conditions that would deem them unsuitable for use by hermit crabs. We inspect every shell before selling it, each shell you purchase will be ready to wash and add to the shell shop. Cracks or holes in the bottom portion of the shell (deeper than just the surface of the shell) will allow the shell water to leak out and are not suitable for hermit crab use. The shell’s opening doesn’t have to be perfectly smooth but they shouldn’t have sharp, broken edges. Superficial cracks, chips, pitting, and other blemishes do not affect the suitability of the shell, they are to be expected as shells are a natural product.
Never use painted shells for hermit crabs, they are toxic. If you purchase a crab with a painted shell, make sure you have a large selection of suitable shells to encourage a quick shell change.
This Intercostalis shell has holes that would allow shell water to leak out.
The chip in this Bruneus shell is an insignificant blemish.
Hermit crabs must be able to fully retract into their shell and block the opening with their largest claw and legs. As hermit crabs grow, they require larger shells, however, it is a misconception that they require a larger shell after every molt. You need to provide at least 3 to 5 extra shells per crab.
The additional shells should range in size from what they are currently occupying (if the current shell is the correct size) to 1/8” larger, or slightly more. Providing shells that are significantly larger than they need will not satisfy this 3 to 5 shell requirement.
If you are buying both round and D-shaped openings for your crab, please note that the same size crab needs a larger D-shaped opening than it would a round opening. There's no set rule of thumb for calculating the difference but D-shaped openings need to be roughly 50% larger than a round opening.
This crab is fully retracted into its Pica shell. Although it fits, it's time to get larger shells.
This crab is unable to full retract into its shell.
If there are not enough suitable shells available, crabs will fight over them. "Shell jacking" is where one crab forcefully removes another to obtain its shell. This event can cause serious or fatal injuries, be sure to always keep plenty of suitable shells in the crabitat. Each and every crab in the crabitat must have at least 3-5 additional shells. For example: 3 crabs requires an additional 9-15 shells.
The points of the arrow indicate where to measure round openings.
The points of the arrow indicate where to measure D-Shaped openings.
This digital caliper displays an inside measurement of 1.149".
This ruler shows an inside measurement of 1 1/8".
The 1.5" circle fits this opening almost perfectly.
Using the circle, find the size that fits best in the opening.
Fold the circle in exactly half and place it in the opening as shown.
Don't have a caliper or tape measure?
This template can't be as precise as a digital caliper but we've tested it on both round and D-shaped openings and it's pretty accurate. This template also serves as a visual aid when shopping in our online store. All of our shells are sold by 1/10" increments, so a 1.50-1.59" shell will have an opening at least 1.50" to just a smidgeon less than 1.60"
If you're unable to measure with a caliper, ruler, or can't print the template, we can help you measure. Take a picture exactly as shown and email it to email@example.com. Make sure the image is in focus and the shell's opening is not tilted or angled, this will distort the measurements. We will measure the correct points on the shell and find the size based on your ruler. Make sure the entire opening of the shell is visible and facing the camera head on. Although this method might not match the accuracy of having the shell in hand, we can get a good enough measurement to point you in the right direction.
1. Remove any stickers from the shells.
2. Add treated freshwater to a large enough pot, place the shells in the water.
3. Bring the pot of water to a boil.
4. Continue boiling for 10 minutes.
5. Turn off the heat, carefully remove the shells and pour out any trapped water.
6. Allow the shells to cool completely before step number 7 or placing in the shell shop.
7. Some crabs may prefer to have their new shells dipped in treated saltwater. This is an optional step but may encourage crabs that otherwise don't seem to take an interest in the new shells.
*DO NOT USE THIS METHOD TO CLEAN SHELLS THAT ARE ALREADY IN THE CRABITAT. You may inadvertently kill a crab that is hidden in a shell. If you feel the need to clean shells from the crabitat, simply rinse them in treated water.