A hermit crab that disappears under the substrate may be molting, and a molt can take a long time. Do not dig up a buried hermit crab just to check on it. Disturbing a molting crab can seriously injure or kill it.
Why do hermit crabs bury themselves?
They may dig for several reasons, including molting, temperature or moisture regulation, and normal exploratory behavior. Molting is especially important because the crab sheds its old exoskeleton and hardens a new one while protected underground.
Should I remove the old exoskeleton?
No. A molting crab commonly eats its shed exoskeleton to recover calcium and other nutrients.
How long can a molt take?
The time varies with the crab's size and condition and can last weeks or longer. Continue maintaining proper heat and humidity without excavating the crab.
What if the crab is on the surface and not moving?
A surface molt requires extra care because other crabs can disturb a vulnerable molter. Avoid unnecessary handling. If you are uncertain whether a crab is dead, do not make the decision based only on immobility.
See What Humidity Do Hermit Crabs Need? and browse Hermit Crab Supplies.