Hermit crabs display many interesting behaviors, each denoting how they feel. These convey certain emotions, such as excitement, curiosity, happiness, defensiveness, anger, and stress.
Hermit crabs are nocturnal animals, so you won’t see much of them during daylight hours. After dusk, hermit crabs emerge from under the substrate and perform certain actions.
As social animals, you can learn how hermit crabs feel based on their actions and interactions.
Common Hermit Crab Social Behaviors
It’s common for hermit crabs to grow bored in an unstimulating environment, so you must understand if your pet hermit crabs are happy or unhappy.
Here are the most common hermit crab behaviors with meanings:
1/ Hiding Behavior
Hiding is arguably the most common of all hermit crab personality traits, especially when new to captivity.
Hermit crabs go through post-purchase syndrome (PPS) when first adopted, hiding to overcome the extreme stress of changing habitats.
Even after hermit crabs adapt to life as pets, expect to find them hiding throughout the day. This is instinctive behavior carried over from the wild. Hermit crabs spend their days buried under sand on the beach, hiding from the sun’s intensity.
Pet hermit crabs will remain nocturnal, so you’re unlikely to see them during the day. They’ll remain buried under the substrate, typically emerging at dusk, especially if you offer food at this time.
Even after dark, hermit crabs may still hide in their shells. Behavioral Processes explain that retreating into the shell is an instinctive reaction for any hermit crab that identifies a threat.
If your hermit crabs are constantly hiding, you must identify why. Something about their environment is making your hermit crabs feel unsafe and insecure.
2/ Digging Behavior
Think of digging as an extension of hiding behavior. Hermit crabs dig in the substrate for recreation and to find themselves a hiding place to burrow into and sleep the day away.
All hermit crab enclosures must have a minimum of six inches of substrate to accommodate this desire to dig. Consider adding more substrate, as this makes it likelier that they’ll have enough territory.
3/ Molting Behavior
Molting is the process of a hermit crab shedding an exoskeleton and growing a replacement. Hermit crabs increase in size and mass during molting and regrow any lost limbs.
Young hermit drabs molt several times in their first year, while adult hermit crabs molt every 18 months. Signs that your hermit crab is preparing to molt include:
- Lethargy and lack of interest in play or exercise.
- Glassy eyes and a dulling of the skin to a shade of gray.
- Eating more than usual and spending more time in the water, as the hermit crab is storing fat and drinking water.
- Digging intensely as though making a tunnel.
During molting, the hermit crab will bury itself deep under the substrate and remain there for several weeks, sometimes as long as three months. A molting hermit crab must never be disturbed.
4/ Mating Behavior
Hermit crabs rarely breed in captivity, as a female hermit crab lays her eggs in the ocean.
Unless you can trick your female hermit crabs into thinking a bathtub of saline water is fit for purpose, they’ll reject advances from males in a habitat.
Despite a lack of interest in breeding, females still come into season while living in captivity. While a female is in heat, she releases unique pheromones that capture the attention of her male tankmates.
If male hermit crabs want to breed, their behavior can become antagonistic – two males may fight for the right to mate. According to the Journal of Experimental Marine Biology and Ecology, a male may also ‘guard’ a female, refusing to allow other hermit crabs close to her.
Males attempt to initiate mating by tapping on a female’s shell. In most instances in captivity, the female will ignore this and hide within the vessel. A hermit crab’s heat cycle lasts three or four days.
When this time passes, the male will lose interest and move on.
5/ Fighting Behavior
The most common reasons for hermit crabs to fall out are disputes over mating rights, battles over territory, or fighting over coveted shells.
Sometimes, hermit crabs will resolve any disputes amicably. For example, if a hermit crab wishes to challenge another for a shell, it will rap upon this vessel. The incumbent hermit crab will either hide and ignore the challenge or accept it.
If the shell’s owner agrees to a duel, the hermit crabs wrestle with their antennae – the winner claims the shell. According to Animal Behavior, hermit crabs of equal size are likelier to battle. If one hermit crab is much smaller than the other, it’ll likely yield.
Unfortunately, not all hermit crab disagreements are solved quite so cordially. Sometimes, a larger, dominant hermit crab will attempt to drag a rival out of its shell by force.
Listen out for loud chirping when two hermit crabs appear to be in conflict. They should be separated if you spot two hermit crabs attempting to pinch each other.
6/ Limb Shedding Behavior
Hermit crabs can regrow lost limbs when they molt, so they may periodically shed their legs or chelipeds.
Shedding limbs shouldn’t be considered normal. Hermit crabs shed limbs when faced with extreme stress, so if you spot that one of your hermit crabs is missing multiple legs, something is amiss.
Hermit crabs also sometimes shed limbs as an act of self-defense. If a hermit crab feels that it’ll be dragged from its shell, it considers losing a limb to be the lesser of two evils.
Shedding a leg or claw distracts a hermit crab’s enemy and provides time to hide.
7/ Pinching Behavior
If you keep hermit crabs as pets, you may be pinched occasionally. Hermit crabs rarely pinch as an act of willful aggression, but they may pinch if feeling threatened.
A hermit crab’s pinch may hurt a little, but it won’t match the intensity of a bite from a cat or small dog. In some cases, a hermit crab pinch can break the skin.
The most common explanation for pinches is that you’ve attempted handling without earning a hermit crab’s trust. There will be times when handling is unavoidable, such as during tank cleaning.
8/ Grooming Behavior
You should also provide two tubs for your hermit crabs. One should contain saline and one fresh water, as hermit crabs will alternate between these two bodies of water.
Hermit crabs clean their skin and the interior of their shells by taking a bath. Hermit crabs poop inside their shell before flicking the waste onto the substrate, but this will only clean a shell so much. Bathing also moistens the gills, aiding breathing.
The tubs should be deep enough for a hermit crab to submerge itself but not so deep it can’t escape. Terrestrial hermit crabs can’t hold their breath indefinitely – most will drown underwater in 20-30 minutes, so install ramps if necessary.
9/ Shell Behavior
We have touched upon the so-called “shell wars” between hermit crabs in our segment on fighting behavior. Hermit crabs may choose to change shells without being challenged, which usually happens after a molt when a hermit crab has outgrown its previous home.
When a hermit crab decides to change shells, all conspecifics in a tank will get involved. The hermit crabs will line up according to size and take turns to try on a now-vacant shell. This chain will continue until all animals are happy.
Hermit crabs almost invariably live alone in their shell – this is the origin of their name. Very occasionally, two small hermit crabs may share a large shell. This suggests the shell is too large and cumbersome to carry alone, but there is a lack of valid alternatives.
Always keep a range of spare shells in a hermit crab habitat so your pets have the option to change if necessary or desired. Ensure these shells come in various shapes and sizes so all the hermit crabs in your care can find the perfect home.
10/ Feeding Behavior
As natural scavengers in the wild, hermit crabs will eat almost anything they can find, which means they value variety. If you provide the same food twice in 24 hours, they may be disinterested in eating.
The best time to feed hermit crabs is dusk, just as they start waking up from a day’s sleep.
Choose food with a strong scent, as Arthropod Structure and Development explains that hermit crabs seek food through smell.
Place a food dish close to a bowl of saline water, as the salty water will stimulate the scent glands in hermit crab antennae. While hermit crabs will eat most anything, especially if it tastes and smells sweet, they need a diet rich in protein and calcium to flourish.