Hermit crabs are amazing animals, albeit often misunderstood. For a start, they are not even crabs in the purest sense. Hermit crabs also have a range of behaviors and physical characteristics that make them unique.
Did you know that hermit crabs can shrink as well as grow during molting? Are you aware of the symbiotic partnership between hermit crabs and sea anemones? Do you know the largest invertebrate in the world, which is part of the hermit crab family?
This guide will take a deep dive into some fun facts about hermit crabs. By the time you’re finished, you will know these animals far better. As well as being interesting, this information will make you a better owner.
Cool Hermit Crab Facts
Are you looking for hermit crab facts and information? Then you’re in the right place. Let’s take a look at 17 fun hermit crab facts that will help you understand these really interesting crustaceans better.
Hermit Crabs are Not Hermits or Crabs
The name, “hermit crab,” is a misnomer. A common definition of a hermit is, “a reclusive or solitary person.” This does not apply to hermit crabs. These animals love the company of their own kind.
In the wild, hermit crabs live in colonies. Sometimes up to as many as 100 hermit crabs live together. They trade shells, protect each other from predators, and generally socialize.
Also, hermit crabs are not true crabs. This is because they are not born with a hard exterior shell. This is why they get shells from other sources. A hermit crab without a shell looks more like a lobster.
So, why are these animals called hermit crabs if neither word is accurate? ‘Hermit’ applies to the fact that hermit crabs rarely abandon their shells. Technically, this means they are always home alone.
As for the crab terminology, hermit crabs are decapod crustaceans, just like crabs. Nature posits that King crab evolved from hermit crabs. Domesticated dogs are not wolves but share 99% of the same DNA. Hermit crabs and crabs have a similarly entwined history.
Hermit Crabs Can Live on Land or Underwater, But Never Both
With over a thousand species of hermit crabs, there is bound to be some variety. What some people do not realize is that hermit crabs are separated into 2 core categories. Some live underwater, and others live on land.
There are 8 core genera of hermit crabs—seven of these live underwater. Marine hermit crabs need to stay wet to breathe. They stick to the ocean floor and usually rely on mollusk shells for shelter.
Aquatic hermit crabs do come onto land periodically. This is never a long stay. The moment the gills of a marine hermit crab dry out, it cannot breathe. They come to dry land to find food or a shell then return to the sea.
Land hermit crabs, meanwhile, have lungs as well as gills. This means that terrestrial hermit crabs can only spend short periods submerged in water. Terrestrial hermit crabs cannot swim and only spend time in the water to bathe and dampen their gills. If they spend too much time underwater, land hermit crabs drown.
All Hermit Crabs are Born in the Ocean
Whether hermit crabs live on land or underwater, they all start their lives in the ocean. When a female is ready to hatch her eggs, she hurls them into the sea. Upon contact with saltwater, these eggs burst open, and the hermit crab life cycle begins.
Hermit crabs start life as larvae, known as zoeae. They toss anywhere from 800 to 50,000 eggs into the ocean. These tiny zoeae float on the ocean surface with plankton. Some die, some are cannibalized, some become whale food – but a hardy few survive.
If zoeae live for around 60 days, they make their way to land evolve into megalopae. These tiny primitive forms of hermit crabs look like spiders and are roughly the size of a thumbnail. If a megalopa survives for 30 days, it burrows under the sand of the beach.
When the megalopa emerges, it has evolved into a juvenile hermit crab. From here, it will seek its first shell and join a colony. Wild hermit crabs always welcome new additions to their habitat.
Hermit Crabs are Right-Handed
A core difference between hermit crabs and ‘real crabs’ is in the pincers. In many species of crab, the pincers are roughly equally sized, so they are ambidextrous. In hermit crabs, the right pincer is much bigger. This means that hermit crabs are technically right-handed.
Hermit crabs use their pincers for several reasons. If you upset your hermit crabs, you’ll know they can pinch humans – and it hurts. Pincers are helpful for self-defense. Hermit crabs also use pincers for climbing, though. They make it easy for hermit crabs to gain traction.
Equally, pincers play a major role in eating for hermit crabs. The animals pick up a food morsel and guide it toward their mouths. From here, two small antennae around the hermit crab’s mouth smell and taste the food.
If the snack is deemed tasty, these antennae will guide it into the mouth. From here, the food is ground down with small mouthparts and swallowed.
Hermit Crabs Shed and Regrow Limbs
Hermit crabs can regrow lost and damaged tissue. This is important as hermit crabs are fragile. They shed limbs when stressed. Hermit crabs also willingly sever their legs if uncomfortable or injured.
Never attempt to pull a hermit crab from its shell. This will result in your pulling off the legs of the crab. Hermit crabs value shells more than limbs. They know the latter will grow back. They focus their energy on guarding the former.
The limbs of hermit crabs regrow during the molting process. It sometimes takes more than one molt to regrow limbs of equivalent length to those lost. Eventually, though, the hermit crab will completely regenerate any shed legs.
In some rare cases, hermit crabs can even regrow eyes. This depends on how much damage was done to an eye. The stalks regenerate, but if the eye was damaged beyond repair, it’s gone for good.
Thankfully hermit crabs do not rely on eyesight to move. They feel their way around using their long antennae. Also, hermit crabs have a keen sense of smell – as long as saltwater is nearby.
Hermit Crabs Need Saltwater and Quiet to Smell and Hear
As discussed, hermit crabs cannot smell without saltwater. Hermit crabs rely on their antennae to smell. When scent particles enter the air, the antennae of hermit crabs start to twitch. This means the hermit crabs are smelling the air and processing the aroma.
As per PloS One, this is only effective when close to saltwater. Without water vapor, hermit crab antennae lack moisture. This leaves hermit crabs with the equivalent of a blocked nose. Always keep saltwater in an aquarium. Without it, your crabs cannot smell their food.
Equally, hermit crabs need a quiet environment to hear. Hermit crabs do not have ears. They detect sound through vibration. A constant, low-level droning or white noise dulls this ability. This can leave hermit crabs distracted and disoriented.
Hermit Crabs Can Grow or Shrink During Molting
All hermit crabs molt. This is the process of shedding an exoskeleton and growing a new one. Ordinarily, this is because the hermit crab is growing in size. Hermit crabs molt several times in their first year or two of life. After this, molts occur brought every 18 months.
In some cases, hermit crabs molt to reduce in size and mass. This is a survival mechanism. Shells are essential for hermit crabs, and larger shells can be hard to find. If hermit crabs outgrow a shell, they can get trapped within. They’d rather this than go without, though.
If hermit crabs are struggling to find appropriate shells, they will shrink during a molt. While this theoretically makes hermit crabs more vulnerable, it offers greater protection. Smaller hermit crabs have a greater range of shells to choose from.
We previously discussed how hermit crabs their name as they do not share shells. Technically, they do – just not with other crabs. Many aquatic hermit crabs in the ocean form a symbiotic relationship with sea anemones.
Sea anemones are small marine animals, named after the anemone plant due to their similar appearance. These anemones attach to the shell of hermit crabs. As per Molecular Phylogenetics and Evolution, this forms a mutually beneficial relationship.
The anemones share food with hermit crabs, relying on the scavenging instincts of their hosts. In return, the anemones provide physical protection. Sea anemones have stinging cells, used to ward off predators that seek to consume hermit crabs.
Hermit Crabs are Particular About Shells
If you’re looking for a new home, you could do worse than following the example of hermit crabs. These animals have a precise methodology for choosing new shells. As this is potentially the permanent home of a hermit crab, it is not a decision to rush.
Hermit crabs like shells that have previously been occupied by a conspecific. When hermit crabs die, they release a distinct pheromone. This alerts other hermit crabs that a shell is about to become vacant. All local hermit crabs will pick up on this scent.
The interested hermit crabs will then line up, largest to smallest. They take it in turns, trying the shell on for size. Once the shell is taken, the resident will relinquish its previous vessel. The trading process then starts again until all hermit crabs are satisfied.
Not all shell negotiations are this amiable. Hermit crabs can come into conflict over shells. If one hermit crab covets the shelter of another, it may challenge it. This is a natural part of hermit crab society.
If hermit crabs get desperate, they can use alternatives to shells. Some hermit crabs use a sponge as a shelter until they find a shell. Wild hermit crabs also use beach trash. Sadly, as per the Journal of Hazardous Materials, this kills almost 60,000 hermit crabs each year.
Hermit Crabs Rarely Breed in Captivity
Hermit crabs cannot be spayed or neutered, so you may be concerned about keeping males and females together. Hermit crabs practically never breed in captivity. As discussed previously, female hermit crabs rely upon the ocean to birth young.
This does not stop males from trying. If a male senses fertility in a female, it will gently rock the shell back and forth. This is hermit crab flirtation. In captivity, the female will usually stay firmly in her shell and ignore the attention.
Do be mindful of this behavior. Male hermit crabs can be determined. They may start ‘guarding’ a female, following her around and attacking other males that approach. This will usually only last a few days. When the fertility window passes, the male loses interest.
If you want to sex your hermit crabs, either out of curiosity or to choose a name, wait for them to leave their shell. Take a look at the legs. If these legs are hairy, the hermit crab is male. If they are smooth, it is female.
You can also check above the third set of legs for gonopores. These are two small holes that are found on female hermit crabs. Semen deposited into the gonopores during mating.
Crustaceana explains that hermit crabs can be intersex. The gonopores usually close after an early molt, though. Intersex hermit crabs then proceed to live as males.
The Largest Crab in the World is a Hermit Crab
Hermit crabs are usually small. One or two hermit crabs can happily live in a 10-gallon aquarium. The exception is the Coconut Crab. This relative of hermit crabs is the Birgus latro, or Coconut Crab. This animal is the largest terrestrial invertebrate in the world.
Also called a Robber Crab or Palm Thief, the Coconut Crab is native to islands around the Pacific and Indian oceans. This crab can grow as big as a trashcan. The largest Coconut Crabs are over 3 feet long and weigh around 9 pounds.
You would not want to get on the wrong side of a Coconut Crab. The impressive pincers of this animal have a force of 740 pounds. That’s comparable to the jaws of a mountain lion. Thankfully, you’re unlikely to encounter this crab. Even if you did, they are largely docile.
Hermit Crabs Have Good Memories
Hermit crabs may not appear like the most intelligent animals, but they have surprisingly good memories. Be careful how you treat a hermit crab. It will remember your scent, and whether you are a friend or foe. It is commonly believed that hermit crabs remember all kinds of things. These include:
- Shells that have previously been occupied
- Painful experiences that should be avoided in future
- What they have eaten recently
- Fellow hermit crabs, and whether they are dominant or aggressive
The latter is particularly important to hermit crabs. These animals follow a strict social hierarchy of dominance and submission. If two hermit crabs crave alpha status, then conflict will arise. This means that such hermit crabs typically stay out of each other’s way.
Hermit Crabs Eat Anything but Have a Sweet Tooth
In the wild, hermit crabs are omnivorous scavengers. When the sun goes down, they emerge from hiding and seek food on the beachfront. Hermit crabs are not fussy eaters. They consume corpses of dead animals, feces, food waste, algae, and sometimes each other.
Marine hermit crabs kept as pets are often considered aquarium janitors. They clean up after the mess made by any resident fish. Hermit crabs happily eat algae growth, keeping it under control.
Fresh fruits and vegetables are also firm favorites. These animals love sweet tastes in particular. Oats with milk, grapes, and bananas are all popular with hermit crabs. Try to bring carrots into their diet, too. These vegetables are good for hermit crabs.
Hermit Crabs are Strictly Nocturnal
Hermit crabs are a popular pet for children, but that may be counterproductive. Hermit crabs are nocturnal and only emerge after dark. This needs to be reflected in their habitat. Hermit crabs need 12-hour cycles of light and dark every day.
Hermit crabs are nocturnal so that they can avoid the light and heat of the sun. Hermit crabs only need a tiny amount of illumination to see. Anything more hurts their eyes. If they get uncomfortable, hermit crabs sever their eyesockets with their pincers.
Never disturb hermit crabs during the day. They will usually be sleeping piled up under substrate or in a hiding place. Hermit crabs are disoriented when they first wake up. Anybody that disturbed their slumber will likely be pinched.
Hermit Crabs Love to Climb
Hermit crabs are natural climbers. The Journal of Crustacean Biology explains that female hermit crabs climb trees to throw their eggs into the ocean. In captivity, the Journal of Ethology tells us that hermit crabs climb aquarium walls to avoid conflict.
Always provide climbing apparatus for hermit crabs in an enclosure. This is the most common form of exercise and recreation for hermit crabs. If they have rocks to climb and vines to ascent, they will be happy and healthy.
Many hermit crabs even climb to the roof of an enclosure and hang like bats. This starts as fun. Climbing is exhausting, though. The hermit crabs hang so they can take a nap. Just be careful. They may try to push the roof open and make an escape.
Hermit Crabs Pee Through Their Face
Male hermit crabs have a penis—a surprisingly large one. As per Royal Society Open Science, a hermit crab’s penis is half the size of its abdomen. This enables the hermit crab to mate without abandoning its shell.
Despite this, hermit crabs do not urinate from a penis. All hermit crabs, regardless of gender, pee from their face. There is a tiny hole beside the antennae. Hermit crabs release microscopic streams of urine from here throughout the day.
Conversely, hermit crabs do poop from an anus (known as the telson). They do this within a shell too. The waste is allowed to build and is then flicked onto the substrate using the rear legs. Hermit crabs also bathe in saltwater to clean messy shells.
Hermit Crabs Verbalize
Hermit crabs are widely considered quiet pets. This does not make them silent, though. Hermit crabs do verbalize. This is known as stridulation. The noise sounds like a cross between a chirping cricket and a croaking frog.
Hermit crabs do not verbalize through a larynx. Instead, it is believed that hermit crabs make noise by scraping their legs against their shell. Verbalization in hermit crabs has many meanings, but most revolve around some level of disgruntlement.
You’ll hear your hermit crabs chirp if you handle them against their will, for example. Hermit crabs will also stridulate if you disturb their sleep. These animals are cranky when they first wake up, especially if disturbed during the day.
The Journal of the Marine Biological Association of the United Kingdom explains that hermit crabs also stridulate in self-defense. This noise is made to scare off rival hermit crabs, especially if they plan to steal their shells. In such cases, hermit crabs also often vibrate inside shells.
We hope that these fun and interesting facts about hermit crabs have helped you gain a little more insight into their world. We’re biased, but we consider hermit crabs the coolest animals around.