Are you sure? land hermit crabs are nocturnal, which means they are active at night while we are sleeping. Hermit crabs are small creatures who eat and drink in small amounts. To be really sure your hermit crab is not eating try this: Smooth out the sand or substrate all around the food and water dish during the day. The next morning check the tank and see if there are any tracks around the dishes. If you see hermie tracks you know your crab was eating while you were sleeping. If you try this for several days and see no tracks, then your crab may not be moving at all. This could be a sign of a molt or possibly a death. Try moving the dishes closer to the crab just in case its too weak to reach them on its own.
If your water is disappearing every night, make sure there is no sand spilling in to the dish. Sand will act like a sponge and draw all the water out of the dish and into the surrounding sand. Often people mistake this for a crab that is drinking huge amounts of water every night. If your water dish is over your UTH, the water may be evaporating.