Hermit crabs are easy pickings for other wildlife, whether on land or underwater.
However, hermit crabs are skilled survivors, employing a range of defensive tactics to avoid becoming a small meal for a larger predatory animal.
If attacked, hermit crabs hide in their shell, 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 do not inspire fear in other wildlife. Hermit crabs are scavengers. They will never attack another animal to eat, with the rare exception of gastropods. In this instance, hermit crabs may attack a snail for its shell.
Hermit crabs have limited protection. As these animals are born without shells, their exoskeleton puts up little resistance against the jaws of a predator. This is why you’ll never find a ‘naked’ hermit crab in the open.
They will only present themselves if they feel appropriately defended. Even then, hermit crabs will not wander the beach with abandon. If you spot a hermit crab in the wild, it is out for a reason. Usually, it will be looking for food a new shell.
How Do Hermit Crabs Detect Predators?
Most animals detect threats by sight, such as a sudden movement. As per PeerJ, hermit crabs are no exception to this rule. An experiment in a laboratory proved that hermit crabs shrink away from visual threats.
Hermit crabs also listen out for danger. Hermit crabs hear by detecting vibrations in the air. If hermit crabs hear something untoward, they hide. If distracted by white noise, such as boat engines, hermit crabs are more vulnerable to predation.
Hermit crabs also use their sense of smell to stay alive. They remember tankmates by scent, as explained by Marine and Freshwater Behavior and Physiology. Hermit crabs use this skill to remember which conspecifics are friend or foe.
The same applies to predators. Hermit crabs have good memories, recalling any animal that meant them harm. The issue is that many hermit crabs only get one encounter with a predator. If they escape, the hermit crab will remember to avoid this animal in the future.
What Eats Hermit Crabs in the Wild?
Hermit crabs are untroubled by humans. They are edible, in that their bodies contain no toxins to humans. They are not a delicacy in any culture, though. When hermit crabs are captured, it’s to be sold as pets, not eaten.
Naturally, wildlife is a different concern. Common hermit crab natural predators can be found by land, sea, and air. This is why hermit crabs need to be constantly vigilant about defending themselves.
The sea is arguably the most dangerous place for hermit crabs. This is most unfortunate for the hundreds of species of hermit crabs that must live underwater. As we’ll discuss shortly, these hermit crabs team with sea anemones for protection.
This is critical for hermit crabs, as marine predators are legion. Any larger fish, for example, will eat a hermit crab. This is not limited to sharks. Traditional sea fish also dine on hermit crabs. Octopi are another constant threat.
Land-based hermit crabs do not live in the ocean but need to spend time in the sea occasionally. These animals are arguably at greater risk as they do not forge symbiotic relationships with sea anemones.
Terrestrial hermit crabs typically spend around 30 minutes in the water a day. This is to keep their gills moist, which aids breathing. Saltwater also sharpens the senses of hermit crabs and provides the opportunity to bathe and clean the shell.
During this period, the hermit crabs will submerge underwater but stay close to the shore. The deeper underwater hermit crabs venture, the more predators they will encounter. As hermit crabs cannot swim, they rarely wander far.
Although hermit crabs are decapod crustaceans, they are not real crabs. A species like the Blue Crab is a natural enemy of the hermit crab. These animals consider hermit crabs an easy meal to overpower and devour.
Hermit crabs do not eat each other, unless already dead. The same cannot be said of true crabs, which often share the same territory as hermit crabs.
A true crab will be larger than a hermit crab, and considerably more antagonistic. They also have more powerful claws. The aforementioned Blue Crab can crush a hermit crab shell in seconds. Without protection, hermit crabs cannot save themselves.
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 are easy pickings for gulls or larger avian predators. Hermit crabs are acutely aware of this fact.
Birds are arguably the most dangerous enemies of all. Hermit crabs have no way of defending themselves against an attack from above. Birds can swoop and grab hermit crabs before they have time to respond.
This means that hermit crabs are careful about where and when they change shells. The few moments it takes to switch from one shell to another is all it takes for a bird to strike. Alas, this is often considered a risk worth taking.
A bird is less likely to attack hermit crabs with a shell. They may still dive to test the strength of a shell. If it’s tough, the bird will likely fly away and look for food elsewhere. Brittle or damaged shells may encourage the bird to attempt a second attack, though.
How Do Hermit Crabs Protect Themselves?
With danger lurking around every corner, hermit crabs rarely feel truly safe. Threats are lying in wait everywhere. This means that they need to quickly learn effective self-defense techniques.
The first step of this is joining a colony. Hermit crabs do not live alone in the wild, despite their name. They typically form colonies of up to 100 members. There is safety in numbers. A single hermit crab may be delicate, but several can be a force to be reckoned with.
If threatened, a hermit crab will defend itself. Like all animals, hermit crabs have no intention of being eaten. As explained by the Journal of Physiology, hermit crabs have a fight-or-flight response to danger. It just manifests differently to that of mammals.
Hermit crabs are rarely considered intelligent animals. They do not have a brain, so to speak. Hermit crabs are smart enough not to start fights they cannot win, though. Coupled with a docile nature, this means that hermit crabs remain invisible where possible.
Unless a wild hermit crab has a reason to be out in the open – seeking food, bathing, or searching for a shell – they stay burrowed under sand or soil. This is why captive hermit crabs bury themselves. It’s an instinct carried over from the animal’s wild days.
As nocturnal animals, hermit crabs also 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 are to encounter antagonistic wildlife.
Terrestrial hermit crabs are likelier to burrow than marine counterparts. Land hermit crabs can breathe while burrowed, so they only emerge when strictly necessary. This safety-first approach serves hermit crabs well.
Hiding in the Shell
It’s no secret that shells are important to hermit crabs. As they do not generate protective shells organically, they source them from elsewhere. As per the Journal of Experimental Marine Biology and Ecology, many traits are considered when choosing shells.
Finding the perfect domicile is a balancing act for hermit crabs. Shells need to be large enough to comfortably fit within, but not too heavy to carry on the animal’s back. All the same, the shell needs to be sturdy enough to offer protection.
When frightened or intimidated, the instinct of many hermit crabs is to hide within the shell. They will remain in this protective barrier until the threat passes. As a thin shell will be torn through like tissue paper, a certain density is essential.
Wild hermit crabs often squabble over shells for this reason. Every hermit crab wants a vessel that strikes the perfect blend of maneuverability and protection. Finding such a shell could be the difference between life and death for hermit crabs.
Hiding in a shell will not always be impactful. Larger animals can shatter a hermit crab shell through sheer force. Alternatively, a stubborn predator may keep attacking the shell, causing significant stress to hermit crabs.
In these instances, hermit crabs cut their losses and flee. As per the Journal of Experimental Biology, how fast hermit crabs move depends on a range of factors. Larger hermit crabs have a longer stride and cover more ground. Lighter shells also increase velocity.
If a hermit crab is at risk of being caught, all is not necessarily lost. If required, hermit crabs shed limbs to aid escape. If a trailing leg is captured, for example, hermit crabs sacrifice this limb to distract the predator. They have five more walking legs to flee with.
This limb will re-grow during the next scheduled molt. This is why hermit crabs consider the loss of a limb a small price to pay for survival. Typically, a hermit crab will hide underground following an attack. The stress of the incident may bring on an immediate molt.
Naturally, hermit crabs also have a ready-made defense mechanism in their anatomy. All hermit crabs have pincers, scientifically known as the chelae. The right pincer is usually dominant and much larger.
Hermit crabs can, and will, defend themselves using the chelae. Any owner that has been pinched will be aware of this. It is a reflex action for hermit crabs. Fighting is not the primary purpose of the chelae, though. Most hermit crabs use their pincers to climb and eat.
The amount of force that is emitted by the pincers depends on the breed. The Coconut Crab, for example, can exert force up to 1,765.2 newtons, according to PLoS One. That’s more force than the jaws of a lion.
This is the exception rather than the rule, though. Coconut crabs are considerably larger than the average hermit crab. So big they will rarely be attacked by any but the boldest of predators.
Typically, hermit crabs will use pincers as a warning or buy time. Average hermit crabs will not exert enough force to kill predators by pinching. They are rarely inclined to do so. Most hermit crabs will pinch to stun or shock a predator then flee.
One of the most fascinating 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. This means that both animals benefit, and neither is harmed.
As per Molecular Phylogenetics and Evolution, hermit crabs typically remove sea anemones from their hiding place and attach them to a shell. Alternatively, the sea anemones may decide to attach to a hermit crab of their own accord.
As sea anemones rarely move around the ocean floor, they benefit from this relationship. By hitching a ride with hermit crabs, the anemones have a greater catchment area for food. They will 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. These surround hermit crabs, like a curtain. This will quickly deter predators, who will seek alternative, safer prey.
Sea anemones can live for as long as 80 years. Hermit crabs, for their part, have a maximum lifespan of half this time. This means that a successful symbiosis could last the full life of a hermit crab. Sea anemones will only look for a new host if necessary.
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 squabbles and competition over shells are the biggest cause of hermit crab fights. For the most part, hermit crabs try to keep these disputes civil. Hermit crabs are docile animals by nature. Things can turn nasty though.
A peaceful transition of shells depends on how feisty and subservient an incumbent occupant is. If a dominant hermit crab demands a shell from a subservient, some will willingly trade. Others will fight, refusing to relinquish their prize.
Thankfully, hermit crabs do not attack each other for food in a cannibalistic frenzy. Hermit crabs are natural scavengers. This means they may eat the cadavers of dead animals – including conspecifics. Live hermit crabs are not a delicacy to their associates, though.
Will Hermit Crabs Kill Each Other?
Hermit crabs try to avoid getting too physical. They understand that their existence is fragile. They do not see the point in killing each other. There is plenty of other wildlife willing to do that for them.
Sometimes, though, hermit crabs have been known to grow antagonistic to the point of fatality. Ordinarily, this stems from a shell fight. If hermit crabs have no shell, they grow increasingly desperate. No shell equals absolutely no protection from predators.
In these instances, a hermit crab may not wait to find a vacant shell on a beach. Instead, it will attempt to tear another hermit crab from its domicile by force. As you can imagine, this is not taken lying down.
Equally, hermit crabs that have not belonged to a colony can go comparatively feral. As per Estuarine, Coastal and Shelf Science, competition for food also sometimes grows ferocious. As hermit crabs are not fussy about what they eat, though, this is rarely an issue.
Hermit crabs that fight to the death will pinch at the eyes, abdomen, and antennae. These are the most delicate parts of hermit crab anatomy. Again, though, allow us to stress. This is rare. Most hermit crabs seek safety in each other’s company, not conflict.
Hermit crabs are savvy. They often live for many years in the wild once they learn how to survive. Many animals could learn lessons in how to negotiate hostile terrain from hermit crabs. In many respects, the biggest danger to wild hermit crabs is well-meaning but misguided humans keeping them in unsuitable captive conditions.