Last Updated on February 17, 2023 by Joanne Harper
Unprotected and carefree hermit crabs would be easy pickings for other wildlife. However, hermit crabs are survivors, employing defensive tactics to avoid becoming a meal for a predatory animal.
Hermit crabs hide in their shell if attacked, which is why strong, sturdy shells are essential. Land hermit crabs may fight back with claws or flee and burrow under the sand.
Marine hermit crabs forge symbiotic relationships with sea anemones. Anemones ward off predators with stinging tentacles in exchange for a share of the hermit crabs’ food.
Are Wild Hermit Crabs at Risk from Predators?
For hermit crabs, dangers are all around them, as they’re small and comparatively docile. Hermit crabs are seen as an easy target by many larger species.
What’s more, hermit crabs don’t inspire fear in other wildlife. Hermit crabs are scavengers, so they rarely attack another animal to eat.
As hermit crabs are born without shells, their exoskeleton puts up little resistance against the jaws or beak of a predator. That’s why you’re unlikely to find a hermit crab without a shell in the open.
Hermit crabs will only present themselves after dark and if they feel appropriately defended.
Even then, hermit crabs won’t wander the beach with abandon. If you see a hermit crab in the wild, it’s exploring for a reason. Usually, it’ll be looking for food, water, or perhaps a new shell.
How Do Hermit Crabs Detect Predators?
Hermit crabs detect threats by sight, such as sudden movements, in their extensive field of vision.
Hermit crabs don’t have good hearing, but they can detect vibrations. If they hear something untoward, they’ll hide. They’re more vulnerable to predation if distracted by white noise, such as boat engines.
Hermit crabs also use their sense of smell to stay alive. According to Marine and Freshwater Behavior and Physiology, they remember tankmates by scent, recalling which conspecifics are friends or foes.
Hermit crabs retain memories, recalling any animal that meant them harm. If the hermit crab escapes a hostile encounter, it’ll remember to avoid them.
What Eats Hermit Crabs in the Wild?
Hermit crabs are untroubled by humans. They’re edible because their bodies contain no toxins to humans but aren’t considered food. When hermit crabs are captured, they’re sold as pets, not eaten.
Naturally, other wildlife is a different concern. Common hermit crabs’ natural predators can be found on land, sea, and air, so they’re vigilant about defending themselves.
Larger sea fish and octopi will eat hermit crabs if they can find them. Fortunately, hermit crabs have a symbiotic relationship with sea anemones, which provides mutual benefits.
Land-based hermit crabs sometimes need to spend a little time in the water, and they’re at greater risk as they don’t forge symbiotic relationships with sea anemones.
Terrestrial hermit crabs spend around 20 minutes in the water daily to keep their gills moist, which is essential for breathing. Saltwater also sharpens the senses and allows bathing.
The hermit crabs will submerge underwater but stay close to the shore. The deeper underwater hermit crabs venture, the more predators they’ll encounter.
Although hermit crabs are decapod crustaceans, they’re not real crabs. So, a species like the Blue Crab is a natural enemy of the hermit crab.
Hermit crabs don’t eat each other unless they’re already dead. The same can’t be said of true crabs, which often share the same territory as hermit crabs.
A true crab will usually be larger and more antagonistic with powerful claws. The Blue Crab can crush a hermit crab shell instantly. Without protection, hermit crabs won’t survive for long.
One of the main reasons that hermit crabs need a shell is to protect themselves from swooping birds. If hermit crabs leave their shell, they’re easy pickings for gulls or larger avian predators.
Birds are arguably the most dangerous enemies of all. Hermit crabs can’t defend themselves from an attack from above, as birds can swoop and grab them before they have time to respond.
Hermit crabs are careful about where and when they change shells. The time it takes to switch from one shell to another is all it takes for a bird to strike.
A bird may test the resilience of a shell but will likely fly away and look for food elsewhere if it’s too tough. However, brittle or damaged shells may encourage the bird to keep trying.
How Do Hermit Crabs Protect Themselves?
With danger lurking around every corner, hermit crabs rarely feel truly safe. Threats are lying in wait everywhere, which means that they need to quickly learn effective self-defense techniques.
The first step of this is joining a colony. Hermit crabs don’t live alone in the wild, despite their name. They form colonies of up to 100 members, as there’s safety in numbers.
If threatened, a hermit crab will defend itself. The Journal of Physiology stated that hermit crabs have a fight-or-flight response to danger.
Hermit crabs aren’t considered intelligent animals. They don’t have a brain, but they’re smart enough not to start fights they can’t win. Coupled with a docile nature, hermit crabs prefer to remain inconspicuous.
Unless a wild hermit crab has a reason to be out in the open – seeking food, bathing, or searching for a shell – it’ll stay burrowed under sand or soil.
This is why captive hermit crabs bury themselves, which is an instinct carried over from the wild.
As nocturnal animals, hermit crabs burrow to avoid the sun. Many hermit crabs build and dig tunnels to negotiate terrain underground. The more time hermit crabs spend underground, the less likely they’ll encounter predatory wildlife.
Terrestrial hermit crabs are likelier to burrow than marine hermit crabs. Land hermit crabs can breathe while burrowed, so they only emerge when necessary, a safety-first approach that serves them well.
Hiding in the Shell
Hermit crabs aren’t born with protective shells, so they source them elsewhere. As per the Journal of Experimental Marine Biology and Ecology, many traits are considered when choosing shells.
Shells must be large enough to comfortably fit in but not too heavy to carry on the back. Ultimately, the shell must be sturdy enough to offer protection from predators and environmental threats.
When frightened or intimidated, the instinct of hermit crabs is to hide in the shell until the threat passes. A certain density is essential because a thin shell will easily be torn through.
Wild hermit crabs often squabble over shells for this reason. Every hermit crab wants a vessel with the right combination of maneuverability and protection.
Hiding in a shell won’t always be impactful because larger animals can shatter it through sheer force. Alternatively, a stubborn predator may continue attacking the shell, causing significant stress.
Hermit crabs cut their losses in these instances and flee as quickly as possible.
As per the Journal of Experimental Biology, how fast hermit crabs move depends on various factors. Larger hermit crabs have a longer stride and cover more ground, and lighter shells increase velocity.
If necessary, hermit crabs sever their limbs to aid escape. For example, hermit crabs may sacrifice a limb if a trailing leg is captured, as they have 5 more walking legs.
This limb will re-grow during the next scheduled molt, which is why hermit crabs consider losing a limb a small price to pay for survival. Usually, a hermit crab will hide underground following an attack.
Hermit crabs have a ready-made defense mechanism in their anatomy. All hermit crabs have claws (called chelae), but the right claw is usually dominant and much larger.
Hermit crabs will defend themselves using the chelae, as any owner that has been pinched knows.
It’s a reflex action for hermit crabs. Fighting isn’t the primary purpose of the chelae, as most hermit crabs use their claws to climb and eat.
The force emitted by the pincers depends on the species, and coconut crabs are much larger than the average hermit crab. According to PLoS One, the Coconut Crab can exert force up to 1,765.2 newtons.
Average-sized hermit crabs won’t exert enough force to kill predators by pinching. Most hermit crabs will pinch to stun or shock a predator before fleeing.
One of the defense mechanisms of marine hermit crabs is a symbiotic relationship with sea anemones.
These two species live in perfect harmony and enjoy a commensalism symbiosis, which means that both animals benefit and neither is harmed.
As per Molecular Phylogenetics and Evolution, hermit crabs remove sea anemones from their hiding place and attach them to a shell. Alternatively, the sea anemones may attach to a hermit crab.
Sea anemones rarely move around the ocean floor, so they benefit from this relationship.
Anemones have a greater catchment area for food by attaching themselves to hermit crabs. They’ll also share any scraps of food left by scavenging hermit crabs.
In return, sea anemones offer protection from predators. When a threat is detected, sea anemones unleash a range of stinging tentacles that’ll deter predators.
Do Hermit Crabs Attack Each Other?
Hermit crabs have enough predators to worry about concerning themselves with in-fighting.
Unfortunately, as with any group of animals that live together, disputes and fights will arise. Hermit crabs can be territorial and live according to a strict social hierarchy.
Territorial disputes and competition over shells are the biggest cause of hermit crab fights. For the most part, hermit crabs try to keep these disputes civil.
Some will willingly trade if a dominant hermit crab demands a shell from a subservient. Others will fight, refusing to relinquish their shell.
However, hermit crabs don’t attack each other for food.
Will Hermit Crabs Kill Each Other?
Hermit crabs avoid getting too physical, as they understand their vulnerability and fragility.
Sometimes, hermit crabs become aggressive and hostile, so they fight to the death. They’ll pinch the most vulnerable body parts, including the eyes, abdomen, and antennae.
If a hermit crab has no shell, it’ll grow increasingly desperate. If so, it may not wait to find a vacant shell on the beach, so it’ll attempt to force another hermit crab from its shell.
As per Estuarine, Coastal, and Shelf Science, competition for food sometimes grows ferocious. As hermit crabs aren’t fussy about what they eat, as long as they have variety, this is rarely an issue.