Home » Finding Shells for Hermit Crabs (with Size Chart + Measurements)
how to measure hermit crab shells

Finding Shells for Hermit Crabs (with Size Chart + Measurements)

Hermit crab shells can be bought from pet stores, craft stores, and online retailers. You can even forage for shells at the beach, but they must be cleaned first.

No matter where you get shells, they must be free from cracks, fractures, holes, and jagged edges. Hermit crabs can modify their shells if necessary, but do your utmost to give them healthy ones.

As hermit crabs grow, they need shells 3/8 – 1/2 an inch wider at the opening than their existing shell. To measure the current shell, lay a ruler across the widest point of the shell’s opening.

Hermit crabs are selective about new shells, so offer 3-5 each. The shells should never be painted because it’s toxic. The best option is natural sea snails, which are roomy and afford protection from falls.

How To Measure Hermit Crab Shells

Hermit crabs don’t grow shells. Instead, they recycle empty gastropod shells and turn them into homes. So, hermies need to trade in their shells for bigger shells as they grow.

You’ll need to measure the shells to ensure they’re big enough to accommodate a hermit crab.

A shell is measured from the widest point of its opening. Using a ruler, measure the hermit crab’s existing shell. Note the diameter of the shell at its widest point.

New shells should be ¼ inch wider than the hermit crab’s existing shell. Pick 3-5 new shells that vary in size to give the hermit crabs several options.

It’s also sensible to match the general shape of the existing shell, especially at the opening. Hermit crabs favor “O” and “D” shape openings.

Hermit crabs make improvements to their shells to make them more suitable.

Selecting Good-Quality Shells

No matter where you’re sourcing shells, look for imperfections, holes, sharp edges, cracks, and fractures.

Hermit crab shells can be found in pet stores or online in bulk. Aside from that, you can often find appropriate shells at craft stores or gift shops.

hermit crab shell size chart

Hermit Crab Shell Size Chart

Here’s a quick chart to reference when sizing up hermit crab shells. Compare the opening of a hermit crab’s existing shell to determine which size category it fits into:

Small Hermit Crab3/8 – ½ inch opening
Medium Hermit Crab½ – 1-inch opening
Large Hermit Crab1 – 1 3/8 inch opening
Jumbo Hermit Crab3 inches or larger opening

Remember, the new shells need to be up to ¼ inch wider than the existing shell. This gives your hermit crabs room to grow and maneuver.

After a molt, they’ll rely on having extra space and turn down sub-optimal shells.  

How To Prepare Shells for Hermit Crabs

Pet stores sell shells that have been sanitized in preparation for being used by hermits.

So, wash the shell to remove any dust or dirt in primed water. Once done, they can be placed straight into the tank afterward.

You must undertake safety measures if you have foraged the shells from your local beach. There’s a range of parasites and bacteria that could befall hermit crabs.

Avoid shells with barnacle growths, algae, or defects like cracks or holes. Most importantly, check there isn’t already an animal using the shell as a home.

Hermit crabs or snails may tuck themselves away from sight. Unfortunately, it’s common for owners to accidentally bring home a new hermit crab.

Once you have a selection of shells, they’ll need to be sterilized:

  1. Boil the shells for 5-10 minutes.
  2. Leave the shells in water and allow them to cool to room temperature.
  3. Remove the shells from the water and remove any trapped water.
  4. Put the clean shells into the tank.  

As discussed, each hermit crab should have 3-5 shells to prevent fighting.

Do Hermit Crabs Like Colorful Shells?

Hermit crabs are small animals with a limited ability to defend themselves.

Their shells are their primary defense against predators for the protection they afford. An additional trait that hermit crabs rely on is their ability to camouflage.

According to the Journal of Experimental Biology, hermit crabs can distinguish the level of contrast between shells and the surrounding environment. The researchers found that hermit crabs would choose shells with minimal contrast over those with strong contrast.

Hermit crabs won’t choose colorful shells unless they match the surrounding environment. If pushed to desperation, a hermit crab may compromise and pick a colored shell. In this case, it’ll be highly stressed, believing it’s overly exposed to predators, which can shorten its lifespan.

Can I Paint My Hermit Crab’s Shell?

Painted shells may be cute, and decorating them can be a fun crafting activity. However, painting hermit crab shells should be avoided.

The paints used to decorate shells are often toxic, even if it says non-toxic on the label. So, all harmful chemicals are leached into the water and absorbed through contact.

Hermit crabs can become irreversibly stuck in a shell if the paint isn’t fully cured. The paint glues the hermit crab into the shell, and there’s no way to remove the hermit crab safely.

It’ll eventually die when it grows too big for the shell if toxins don’t kill it first.

my hermit crab is too big for its shell

How To Help Hermit Crabs Switch Shells

Never force a hermit crab to leave its shell. Even if you know it needs to move house, removing it unwillingly from a shell is a bad idea.

Aside from traumatizing the hermit crab, you risk wounding it, perhaps fatally. There are things you can do to encourage a hermit crab to move.

Hermit crabs can be fussy when selecting a new shell, even if their current one is a tight fit. They can become very attached to a shell and reluctant to leave.

When a hermit crab rejects new shells, offer it some new ones. Look for shells with different colors, shapes, and openings. You can try a different shell type if it’s right for hermit crabs.

Ensure the substrate is deep enough for the hermit crab to burrow and submerge. Depending on the hermit crab’s size, this may mean 3-8 inches of substrate.

Hermit crabs often molt before changing shells, and they must burrow.

My Hermit Crab Is Too Big For Its Shell

Keep spare shells in the tank ready for a hermit crab needing to change shells. However, sometimes hermit crabs reject all the shells on offer, and you’re none the wiser.

It is difficult to track a hermit crab’s growth accurately. Instead, perform a quick visual test to monitor when a hermit crab needs a new shell.

Pick up the hermit crab and angle it so the shell’s opening faces you. Check how easily it can retract into the shell. It’s getting too big for the shell if it struggles to hide.

This isn’t the most reliable way to judge when a hermit crab needs a shell change. Hermit crabs change shells roughly twice every 12-18 months, so keep a wide variety in the tank.

Hermit crabs may also change shells on a whim. If a hermit crab finds a shell it likes more than its current shell, it may swap immediately. If it’s preparing to molt, it may swap shells in preparation.

Large hermit crab shells can be harder to find, so you may need to visit a specialty aquarium.

Best Shells for Hermit Crabs

Certain shells are more suited to hermit crabs than others. As discovered by Animal Behaviour, hermit crabs show a preference for the shells of certain species.

Avoid shells used by land snails because they’re too fragile, even for a hermit crab. Choosing the shells left behind by sea snails is recommended. Look for shells from the following species:

  • Turbo Snails – Thick shells with a round opening.
  • Murex Snails – Larger shells with spines or lumps.
  • Babylonia Snails – Solid shells with beautiful patterns.
  • Nerita Polita Snails – Good shells for very small hermit crabs.

Hermit crabs may have different preferences depending on their size, body shape, and species. Different shells from various species can be good if your hermit crab is selective.