How to Choose Hermit Crab Shells: The Best Sizes and Shapes
It is important to keep appropriately sized shells in your hermit crabs' tank so they have the opportunity to try out new homes. This article will show you how to select the correct shells for your hermit crabs based on their size, environment, and species.
Every shell is different, so before reaching into the $2.99 shell box at the pet store, get the information you need to measure and select the best shells and avoid wasting money on inappropriate ones.
What You'll Learn
- How to Determine the Proper Shell Size
- How to Buy Shells Online
- How to Choose a Comfortable Shell for Your Crab
- How to Clean and Prepare the Shells
- How Hermit Crabs Change Their Shells
How to Determine the Proper Shell Size
Shell size is one of the most important considerations for choosing hermit crab shells. While most seashells sold for decoration are described by their total width (for example, 3 inches from end to end), the only measurement that matters for your crabs is the diameter of the opening.
Measuring the Diameter of the Opening
Shell size is measured across the longest diameter of the opening. Shell calipers are sold to accurately measure shell openings, but you can get a fairly accurate measurement by eyeballing the opening and a ruler.
- Small hermit crabs usually inhabit shells with 3/8" to 1/2" openings.
- Medium crabs have shell openings ranging from 1/2" to 1".
- Large crabs have shell openings ranging from 1" to 1 3/8".
- Jumbo crabs live in shells with up to 3" openings or larger.
Once you have determined the size of your crab, select a few shells that are 1/8- to 1/4-inch wider than the hermit crab's current shell. Also, try to match the shape of the opening, especially if the crab has consistently chosen shells with round or D-shaped openings.
You can also buy convenient variety packs with shells of appropriate sizes for small and medium hermit crabs. However, the individual shells in a pack are not labeled with measurements, so purchasing shells this way won't help you learn the size of your crab—so you'll be faced with the same dilemma for future purchases.
Do Not Buy Painted Shells
A word of warning: Painted shells are hazardous to the health of your hermit crabs.
How to Buy Shells Online
If you do not live near the ocean, you probably do not have any seashell shops nearby. Depending on the size of your crabs, you may be able to get shells at the pet store or even at a craft store, but otherwise it is best to shop for top-quality shells online at standardized sizes.
Advice for Ordering Online
Ordering online can be tricky, but until you place and receive an order for a specific size and actually see the shells next to your hermit crab, it can be difficult to know what size she needs. If you are unsure, then purchase several different shells and sizes:
- two shells that are the size you think you want
- one shell that is 1/8" smaller
- one or two shells that are 1/8" larger
Once you've ordered and found the right shell, simply remember your crab's size; in the future, you can select shells that are one size larger.
- Most seashell shops will sell shells based on the outside measurements of the shell. Only shells sold specifically for hermit crabs will include the opening diameter measurement. It is very difficult to order shells based on exterior measurements alone.
- Never buy painted shells because they are unsafe for your hermit crabs. Polished and etched natural shells are a beautiful alternative if you don't like the rugged, all-natural look.
Online Store Suggestion
- Hermit Crab Shells at The Hermit Crab Patch
The Hermit Crab Patch is an educational website that only sells products that are healthy for your crabs. You will find a good selection of shells at the best prices I've found online, organized by opening shape, size, and natural/polished finish.
Where do you usually get hermit crab shells?
How to Choose a Comfortable Shell for Your Crab
Most common hermit crabs, especially Purple Pinchers (C. clypeatus), prefer shells with round openings. Other species of hermit crabs, such as Ecuadorians (C. compressus), have been known to prefer shells with D-shaped openings because their bodies are flatter and they are better able to protect themselves in shells with D-shaped openings.
In addition to considering the size and opening of the shell, you should only buy natural, polished, or etched shells. Remember, painted shells are hazardous to the health of your hermit crabs. If your child wants a decorated shell, there are many beautiful natural shells safely etched with dolphins, palm trees, and other designs.
Turbo, Murex, and Other Shells With Round Openings
Turbo shells are probably the best choice for hermit crabs of any size. With a broad, round opening and a heavy, thick construction, these shells are roomy and offer good protection. There are many types of turbo shells available in all-natural, polished, and etched designs (exposing the white pearlescent layer beneath the dark exterior of the shell).
- Magpie, Green Turbo, Turbo Cinerius, Turbo Stripe, and Turbo Petholatus shells are readily available online and are quite affordable.
- For more expensive tastes or for jumbo crabs, try the Jade Turbo or the very beautiful Turbo Sarmaticus shells.
- Murex shells are more structurally lavish than turbo shells, featuring spines and lumps. These may be more attractive for their shape, but know that a hermit crab is not likely to choose a shell with large branches or spikes because it will just make it more difficult to navigate the "crabitat" (crab habitat).
- Pink Murex shells are very commonly found in craft stores at all sizes and are very inexpensive.
- Apple Murex shells are available as well in a nice mix of browns.
Babylonia, Whale Eye, and Other Shells With D-Shaped Openings
Babylonia shells are a nice mix of brown and white and are readily available for both small and large crabs. These shells are common in pet stores, craft stores, and online shell stores.
Other shells with D-shaped openings include the following:
- Nerita Polita shells (for the smallest of crabs)
- Whale Eye shells
- Shark Eye shells
- Crown Conch
- Nutmeg shells
Land Snail Shells: Not Recommended
The shells made by land snails are usually much thinner and more lightweight than those made by sea snails (Turbo, Babylonia, etc.). Generally, sea snail shells are preferred over land snail shells, so these are not recommended.
How to Clean and Prepare the Shells
All shells must be prepared before you place them in the crabitat to ensure that they are safe for your crabs. Shells sold at craft stores are usually bleached beforehand, leaving chemicals that could harm the crab.
Shell Cleaning Instructions
- Discard shells with unnatural cracks, holes, or jagged edges that may harm the crabs.
- Dechlorinate enough warm water to cover the shells three times over.
- Add 1/3 of the water to a bowl and stir in baking soda (about 1 tsp per cup of water).
- Soak the shells in the baking soda solution for 10 minutes. Be sure that the air bubbles out of each shell.
- Shake each hermit crab shell over the sink to drain the water.
- Add 1/3 of the dechlorinated water to a clean bowl and stir in aquarium salt mix, according to the directions on the package.
- Soak the shells for 5 minutes.
- Shake each hermit crab shell over the sink to drain the water.
- Repeat steps 6–8 with fresh dechlorinated water.
Ready for Crabs!
Now the shells are ready for your hermit crabs! Place the shells with the opening facing up to entice the crabs to inspect them, but be patient—only the crab will know when it needs to switch shells and which candidate will be the most comfortable. Inevitably, unused shells will fill up with sand over time, so be sure to clean them occasionally with dechlorinated fresh water.
How Hermit Crabs Change Their Shells
When a hermit crab is ready to change shells, it may need to try out several shells before settling on a new home. Purple Pincher crabs (C. Clypeatus) are particularly likely to switch shells several times in the span of an hour or two, while other crabs may spend more time looking for the perfect shell.
After inspecting the inside of the shell with their legs and antennae, the crab will carefully position the shell. Rising up out of its current shell, the crab will swing its soft white abdomen over and into the new shell and curl down into it. After up to an hour of rolling around and inspecting the new shell, the actual shell switch happens in less than a second!
If you have several crabs that are the same size, they may have loud vocal and physical contests over shells. While these are rarely meant to cause harm, the battles can become dangerous, and you may need to separate the crabs. However, if you have provided enough sand, the crabs should be able to bury themselves to get out of the situation.
Fights are very common in the following scenario, and there is nothing you can do about them besides separating the crabs and buying more shells:
- Crab A switches to a new shell.
- Crab B switches into Crab A's old shell.
- Crab A doesn't like the new shell and wants the old shell back.
- Crab B loves the shell and won't give it back.
If you notice the crabs making noises back and forth or trying to steal shells, buy a few more shells for them to choose from. I had a crab who held a grudge over this scenario for more than a month: Crab B didn't stay above ground for more than an hour at a time until Crab A switched into a new shell and was no longer harassing B for stealing her shell!
Don't Make These Mistakes
Be careful not to make the following mistakes with your hermit crabs:
- Do not remove the old shell; the crab may need to switch back into it.
- Provide at least two shells that are the proper size for your crab.
- If you notice crabs fighting over shells, give them more shells to choose from.
- Never try to force a crab to switch shells.
Some Crabs Change More Often Than Others
How many consecutive shell changes have you seen a single crab make?
With the exception of the first photo from flickr, the hermit crab and shell photos used on this page were taken by the author, fritteritter; other photos were taken by photographers at sxc.hu and used with permission.