Hermit crabs need deep, stable substrate, especially when it’s time to molt.

The setup itself is simple. Use the right mix, give them plenty of depth, and make sure it holds its shape.

Why Do Hermit Crabs Go Underground?

Going underground is normal. Sometimes a crab may disappear for a short time. Other times, it may be preparing to molt and stay buried for weeks or even months.

If a crab disappears, leave it alone. You may not know whether it’s molting until it comes back up, and digging up a molting crab can be dangerous.

What Happens During a Molt?

Most hermit crabs molt underground. They dig a chamber, shed their old exoskeleton, and stay buried while the new one hardens.

The substrate needs to be deep enough for your crabs to fully bury themselves and stable enough to hold its shape while they’re underground.

What’s the Best Substrate?

Mix 5 parts play sand with 1 part coco fiber.

The sand provides structure, while the coco fiber helps hold moisture. Mix them together thoroughly rather than layering them.

How Deep Should It Be?

Use at least 6 inches of substrate, or three times the height of your largest crab, whichever is deeper.

As your crabs grow, add more substrate when needed.

How Wet Should It Be?

Aim for sandcastle consistency.

Squeeze a handful. It should hold its shape without dripping water.

Falls apart = too dry.
Drips water = too wet.

What Substrates Should You Avoid?

Avoid calcium sand, reptile sand, aquarium gravel, pine or cedar shavings, bark mulch, and coconut husk chips as the main substrate.

Do You Need to Change the Substrate?

Usually, no.

Remove food and debris from the surface, but don’t routinely dig through or replace the substrate. A crab may be molting underneath.

A full substrate change is generally only needed after a serious problem, such as an infestation or flood. Properly set up, substrate can stay in the crabitat long-term.