While hermit crabs differ from traditional crabs in most respects, they share one defining characteristic – 10 legs, the foremost of which contain prominent claws or chelipeds. One claw of the hermit crab will be noticeably more prominent than the other.
The bigger claw depends on the hermit crab species. The aquatic Paguridae family are called “right-handed hermit crabs” as their right claw is larger, while the Diogenidae family are dubbed left-handed for the opposite reason. Most terrestrial hermit crabs have a larger left claw.
The primary use of the large claw is for protection and self-defense. Competition for the best shells can become fierce among hermit crabs. The large claw is used to block the entrance to a shell while a hermit crab is sleeping, preventing the shell from being stolen.
The large claw is used in combat if a hermit crab is forced to fight and tears food into chunks small enough for the maxillipeds to move into the mouth. The smaller claw will pick up small foodstuffs and pass water into the mouth when drinking.
Both claws are vital to a hermit crab’s daily life, ensuring it can climb, dig, eat, and protect itself. The claws may fall off during a molt but invariably grow back. When this happens, the size discrepancy between the left and right claws remains.
What Are Hermit Crabs’ Claws Called?
The scientific name for a hermit crab’s claws is chelipeds.
The chelipeds make up the two frontmost legs, with four additional pairs of legs behind. All hermit crabs have chelipeds – if they break or fall off, the claws regrow during the hermit crab’s next molt.
Marine Ecology explains how the larger cheliped can be used to sex a hermit crab. Males have larger claws than females, especially after a first molt.
A prominent left cheliped is seen as a desirable trait in hermit crabs, as females consider those with bigger claws superior breeding partners.
Regardless of sex, all crabs have a size discrepancy between the left and right chelipeds.
Why Do Hermit Crabs Have One Big Claw?
To fully answer this question, we must understand what hermit crabs use their claws for. The chelipeds are multi-functional, and each claw has a range of purposes, including:
Digging and Climbing
Hermit crabs love to climb, whether in the wild or captivity. If you’re keeping hermit crabs in an aquarium, you should get a range of climbing toys to keep your pets entertained. Both chelipeds are essential for climbing.
When climbing, a hermit crab seeks a small protrusion on a surface. Once identified, the hermit crab wraps its legs around this protrusion and hoists itself up. In some cases, the powerful large cheliped is vital to gaining enough grip and traction to climb.
An alternative to climbing is for a hermit crab to dig and bury itself under the sand – or, in the case of captive hermit crabs, aquarium substrate. This behavior occurs immediately before sleep or molting. Alternatively, it could be a way to hide from predators or the sun’s heat.
The larger claw will do most of the digging due to sheer size logistics. The smaller claw will add finesse and help the hermit crab cover itself once burrowed.
Once under the substrate, a hermit crab won’t wish to be disturbed until it emerges to eat.
Protecting a Shell
Hermit crabs take their shells very seriously. Once an optimum shell is acquired, it may be coveted by others. Behavior explains how negotiations for shells between hermit crabs can be respectful and mutually beneficial. Alas, this isn’t always the case.
Like all animals, hermit crabs can be prone to acts of physical dominance. If a smaller hermit crab has sourced an oversized shell, another hermit crab may look to steal it. Sometimes, this involves reaching into the shell and dragging the unwilling incumbent out by force.
This will be traumatic for the victim and best avoided. Consequently, hermit crabs use their large claw to block the opening to their shell. Hermit crabs are attracted to shells with small entry holes, with their cheliped creating an unmoving protective barricade.
Blocking the claw doesn’t mean a hermit crab can retain its shell unchallenged. Other hermit crabs may still initiate a challenge, rapping on the shell with their claws.
Using the large claw as a fence keeps the occupant safe if it remains in hiding.
Fighting and Self-Defense
Hermit crabs typically avoid physical combat where possible and are mainly peaceful. However, wild hermit crabs live in colonies of up to 100 or more, so disagreements invariably arise. In such instances, the large claw will be used as a weapon.
As per Behavioral Ecology and Sociobiology, cheliped size is initially used as a deterrent. Hermit crabs with huge claws may intimidate others, and they flex these appendages to frighten competitors away from food, shells, territory, or potential breeding partners.
Fights can break out if the sight of a claw does not deter an aggressive hermit crab. If hermit crabs are playing, they’ll wrestle with their antennae or test their strength by pushing and shoving each other. If pinching with the large claw, all pretense of friendliness is gone.
If you find captive hermit crabs attacking each other with pinchers, separate them. When hermit crabs are provoked into a skirmish, they fight to win, often using the large cheliped to sever limbs or eye stalks.
Naturally, hermit crabs also have other enemies in the wild, including true crabs and various species of fish and birds. While hermit crabs prefer to hide within their shell, climb a tree, or dig underground to protect themselves, they fight back with their large claw if no alternative exists.
Eating and Hydrating
Both chelipeds play a significant role in a hermit crab’s diet and hydration needs.
Hermit crabs don’t have teeth, so they can’t chew food. The large claw holds and cuts static food down to size. Hermit crabs are scavengers, so they rarely hunt live prey.
Once the large claw has cut the food into bite-sized chunks, the small cheliped moves the morsels toward the mouth. Here, the maxillipeds – small mouthparts – retrieve the food, move it into the mouth, and the hermit crab can swallow and digest.
A similar approach applies to hydration, although there’s no need for the large claw when a hermit crab drinks. Once a water source is located, hermit crabs guide water toward the mouth using their small claw until their hydration needs are met.
As discussed, the large claw of a hermit crab plays an essential role in mating. Females are intuitively drawn to hermit crabs with prominent large claws.
Marine Biology suggests that a substantial cheliped helps a male guard a mate, keeping rivals away. Additionally, hermit crabs with bigger chelipeds are more likely to triumph if forced to fight an opponent for the right to breed.
The large claw of a hermit crab is also used during mating, primarily to hold a female still. Hermit crabs don’t leave their shells unless strictly necessary and, wherever possible, will mate within the shell.
A male hermit crab’s penis is roughly half the length of its body, so it can mate without the risk of leaving a shell or forcing a female to do so.
Typically, a male instigates breeding by holding a female in place with one claw, then tapping and rocking the shell with the other. From here, the invitation to mate will be accepted or declined.
Never be alarmed if you notice that your hermit crab has claws of different sizes because this is a perfectly natural part of hermit crab anatomy. Whether the larger cheliped is on the left or the right of the body, both claws play an essential role in the hermit crab’s daily routines.