the basics of Hermit Crab Shells
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.
Cracks and Holes
This Intercostalis shell has holes that would allow shell water to leak out.
Superficial Blemishes
The chip in this Bruneus shell is an insignificant blemish.
Fully Retracted
This crab is fully retracted into its Pica shell. Although it fits, it's time to get larger shells.
Too Small
This crab is unable to full retract into its shell.
Shell Jacking
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.
measuring hermit crab shells
Round Openings
Measuring with a Caliper
D-Shaped Openings
The points of the arrow indicate where to measure round openings.
D-Shaped Openings
Measuring with a Caliper
D-Shaped Openings
The points of the arrow indicate where to measure D-Shaped openings.
Measuring with a Caliper
Measuring with a Caliper
Measuring with a Caliper
This digital caliper displays an inside measurement of 1.149".
Measuring with a Ruler
Measuring with our Template
Measuring with a Caliper
This ruler shows an inside measurement of 1 1/8".
Measuring with our Template
Measuring with our Template
Measuring with our Template
The 1.5" circle fits this opening almost perfectly.
Using our template
Round Openings
D Shaped Openings
D Shaped Openings
Using the circle, find the size that fits best in the opening.
D Shaped Openings
D Shaped Openings
D Shaped Openings
Fold the circle in exactly half and place it in the opening as shown.
Need help measuring?
Email a precise photo and we will measure for you!
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 info@hermitharbor.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.
preparing new shells
You need to clean new shells before adding them to the crabitat!
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.