As prey animals, burrowing in the sand is among hermit crabs’ natural behaviors.
Hermit crabs dig holes when searching for food, resting, occupying their time, or seeking respite. They may bury themselves for days when feeling overwhelmed or concerned about their safety.
If a hermit crab is due to molt, it could be 4-8 weeks before it resurfaces. Many owners don’t see their pet hermit crabs for so long that they mistakenly think they’ve died.
Why Hermit Crabs Burrow Themselves
Small and medium-sized hermit crabs need at least 4 inches of sand to burrow. However, large hermit crabs need a much deeper substrate, ideally 3-4 times their size.
Here are the reasons why hermit crabs bury themselves:
Recreational Activity
Aside from climbing steep inclines, digging is a favored activity. Some seemingly dig holes for no reason.
Sand is easy to burrow into and replicates hermit crabs’ natural environment. The sand should be moist, which can be achieved with an 80% humidity level.
Sometimes, you’ll observe hermit crabs knocking over their water vessels to generate more humidity.
How Hermit Crabs Dig
Hermit crabs have claws of disparate sizes. The large claw (the cheliped) does most of the digging, as it can move more sand in one fluid motion.
The hermit crab utilizes the smaller claw for digging finesse. This claw can move small amounts of sand so the hermit crab can climb into the hole or move about the substrate.
The small claw is used to cover the hermit crab with sand once it has finished burrowing. Once the hermit crab feels secure under the sand, it tucks its claws into the shell to protect itself.
How Deep Hermit Crabs Dig Holes
Most hermit crabs dig at least 3-4 inches under the substrate. A wild hermit crab may dig deeper, especially if it’s a hot day and wants to regulate its temperature.
If it’s large or has a prominent shell, it may dig a deeper hole. Caribbean hermit crabs (purple pinchers) can grow in size, reaching 2-6 inches.
Foraging for Food
Hermit crabs need a varied diet. According to the Journal of Experimental Marine Biology and Ecology, hermit crabs gravitate toward food they haven’t recently consumed.
If you give hermit crabs the same meal for 2 days in a row, they may not eat it. Instead, they may bury the food for later. Hermit crabs are scavengers, so they’ll traverse the coastlines for sustenance.
Fear And Anxiety
Hermit crabs take to adapt to change and adjust to life in captivity. When introducing a new hermit crab to a tank, expect them to bury themselves for several days.
A new hermit crab may emerge at night when the home is quiet and feels safer.
While keeping a small colony of hermit crabs in a tank is advisable, you must do your utmost to ensure they get along. Sometimes, disputes arise over territory, mating rights, or shells.
If a hermit crab raps on a shell with its claws, it challenges the occupant. Another hermit crab covets the shell and invites the owner to exchange it or fight for the right to wear it.
Some hermit crabs accept the challenge and wrestle for the shell, while others respond with fear, remaining in their shells or burrowing underground.
Privacy
Wild hermit crabs live in colonies of up to 100 animals. Because they feel safer among their species, it’s recommended that many hermit crabs be kept in a large tank.
Even the most extroverted hermit crab needs time alone. Sometimes, hermit crabs burrow and hide underground for solitude, so it isn’t necessarily sleeping.
Temperature Regulation
Wild hermit crabs live in scorching weather conditions, usually on beaches.
While shells offer protection from the sun’s UV rays, most hermit crabs spend their days burrowed under the sand to regulate their temperature.
Captive hermit crabs have a heat lamp because they can’t self-regulate their temperature. They may burrow for temporary respite if they get too hot in their tank.
Hermit crabs also need humidity, so they may dig a hole to find moisture. Without sufficient humidity, land-based hermit crabs can’t breathe and will perish.
Sleep
Hermit crabs burrow and sleep for 6-8 hours under the substrate during daylight hours. Avoid disturbing sleeping hermit crabs and wait for them to awaken naturally when it’s dark.
Molting
All hermit crabs molt several times in the first year and then every 18 months.
Molting is the process of shedding the exoskeleton and growing a replacement. It’s often accompanied by increased size and mass, especially in young hermit crabs.
It can take a hermit crab 4-8 weeks to complete a molt, requiring complete privacy. The signs a hermit crab is about to molt include:
- Skin color fading to gray.
- Eyes are becoming glassy and glazed.
- Growing tired and showing less interest in play or interaction.
- Eating and drinking more than usual to store fat and water.
As the hermit crab is devoid of an exoskeleton when molting, it feels particularly vulnerable.
Molting vs. Dead
The hermit crab will remain buried under the substrate for so long you may think it’s dead. However, you shouldn’t dig up a hermit crab to check if it’s still alive.
In an unwelcome irony, the shock of disturbing a molt could kill the hermit crab. Instead, open the tank and sniff the air. Dead hermit crabs have an unmistakable aroma of rotting fish.
Consider how other hermit crabs are behaving. According to Ecology and Evolution, hermit crabs are attracted to the pheromones of their dead. They’ll check if a now-vacant shell is a suitable upgrade.
If a hermit crab is molting and not dead, its tankmates will leave it alone.
Sickness
Hermit crabs can live for 20-30 years if well cared for, but they can grow unwell. If so, the hermit crab will seek a quiet place to recover, usually by burrowing under the substrate.
Ensure the tank adheres to the 80/80 rule – a temperature of 80°F and a humidity level of 80%. Check the skin, as this signifies it’s about to molt or something is amiss, like a mite infestation.
Hermit crabs can live long lives in captivity, but all living creatures eventually die. The hermit crab may become more withdrawn and isolate itself when the end is near.
Burying Itself To Die
If a hermit crab believes it’ll soon die, it may bury itself and pass away privately. Some hermit crabs vacate their shells when dying so other colony members can use them.
Avoid Digging Up Hermit Crabs
Digging hermit crabs violates their sense of security, so they shouldn’t be readily disturbed.
You can spot-clean the substrate in the tank while a hermit crab is burrowed. Only remove the topmost layer. Wait for the hermit crabs to wake up and grow active before a deep clean.
If a hermit crab has died, you’ll have little choice but to dig it up. If this isn’t the case, leave the hermit crab buried for as long as it wishes to remain this way.
