Hermit crabs are fascinating little creatures that have captured the hearts of pet owners everywhere. One of the most common questions people have about hermit crabs is: how many legs do they have?
Despite their name, hermit crabs are highly social animals that thrive in groups. Their unique bodies and behaviors make them a joy to observe. Let’s take a closer look at how many legs hermit crabs have, and what they use them for.
The Basic Hermit Crab Body Plan
Hermit crabs belong to the taxonomic order Decapoda, which comes from the Greek words “deka” meaning ten, and “poda” meaning foot. This order contains crabs, shrimps, lobsters, crayfish, and other crustaceans.
As decapod creatures, hermit crabs have ten total legs. Their body structure includes:
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Cephalothorax (head region) Houses the hermit crab’s eyes, mouthparts, antennae, and 5 pairs of legs
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Abdomen: Soft, unsegmented body region that houses internal organs. The abdomen lacks a hard covering, so hermit crabs borrow empty snail shells for protection.
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10 legs: Used for walking, climbing, food handling, and tactile sensing.
Now let’s take a closer look at each pair of legs and their specialized functions
The 6 Legs on the Cephalothorax
The cephalothorax contains the hermit crab’s head and thorax fused together. It houses 6 pairs of jointed legs used for mobility. Each leg has a specialized role:
1. First Pair – Chelipeds
The frontmost pair of legs are called the chelipeds These are the large, claw-like legs that give the hermit crab its classic pinch
The chelipeds are used for:
- Defense and territorial fights
- Climbing and holding onto surfaces
- Handling food items to bring to the mouth
Male hermit crabs have larger chelipeds than females. The dominant claw is usually larger as well.
2. Second Pair – Walking Legs
The next pair back are the walking legs. As the name suggests, these legs are used primarily for locomotion on land.
They allow the hermit crab to walk and climb effectively on a variety of terrain. The walking legs work coordinately with the remaining legs to provide mobility.
3. Third Pair – Walking Legs
This third set of legs is also used for walking. They provide additional support and mobility when exploring the environment.
4. Fourth Pair – Grooming Legs
The fourth pair of cephalothorax legs are thinner and more dexterous than the forward pairs. These specialized grooming legs allow the hermit crab to clean itself and pick food particles out of its shell.
Grooming is important for hermit crabs to keep themselves and their borrowed shells clean.
5. Fifth Pair – Grooming Legs
The last pair of legs on the cephalothorax are also used for grooming the eyes, antennae, and shell interior.
Having two pairs of nimble grooming legs allows hermit crabs to properly care for themselves.
The 4 Abdominal Legs
The hermit crab abdomen is soft and vulnerable without the protection of a shell. Four smaller pairs of legs extend from the abdomen:
6. First Pair – Abdominal Legs
These legs have hook-like dactyls for securely gripping the spiraled interior of the snail shell. This keeps the crab stable and locked inside its mobile shelter.
7. Second Pair – Abdominal Legs
The last pair also has specialized dactyls to keep the abdomen braced inside the shell opening while walking and climbing.
Importance of All 10 Legs
As we’ve seen, each of the hermit crab’s ten legs plays an integral role in its survival. The front legs allow it to interact with its environment by climbing, foraging, fighting, and grooming.
The smaller abdominal legs lock the unprotected abdomen in place inside the adopted shell where the crab’s vital organs are housed.
Losing any of its ten legs would be detrimental and make survival much harder for a hermit crab. Their leg anatomy reveals the specific evolutionary niche these animals fill.
Frequently Asked Questions
Now that we’ve explored how many legs hermit crabs have and their functions, here are answers to some other common questions:
Do hermit crabs grow their legs back?
Yes, when a hermit crab loses a leg, it is able to regenerate a replacement leg over a series of molts. The new leg will be smaller initially but grows back to normal size after subsequent molts.
Why do hermit crabs stack up on top of each other?
Hermit crabs sometimes climb on top of each other in piles. One reason is competition over limited shell resources. Crabs stack up to try accessing an available shell.
Do hermit crabs have claws?
The two front legs (chelipeds) end in large claws or pincers that give hermit crabs their grasping power and distinctive look. Males have larger claws than females.
How do hermit crabs mate?
Hermit crabs reproduce by the male transferring sperm packets to the female’s abdomen. This occurs when the crabs form a double-stack with the male on top.
Are hermit crabs deaf?
Hermit crabs do not have ears or eardrums. However, they can detect vibrations through sensory hairs on their legs. Their sense of smell is their primary sense.
Hermit Crab Locomotion
Hermit crabs use coordinated movements of their ten legs to travel over land and surfaces. Here are some of the most common forms of hermit crab locomotion:
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Walking: Alternating front leg movements, like terrestrial animals
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Climbing: Gripping with chelipeds and walking legs to ascend surfaces
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Digging: Using chelipeds and walking legs to burrow into sand or soil
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Righting: Flipping themselves over using their legs if tipped upside down
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Shell dragging: Pulling along a heavier shell by walking backward with front legs
Their versatile appendages allow hermit crabs to thrive in their beach and tidepool environments.
Conclusion
Part of what makes hermit crabs so endearing is watching them lumber around on their ten jointed legs, investigating their surroundings. Those ten legs allow them to fully engage with their habitat.
Understanding the specialized roles of each leg also provides insight into how these animals evolved. The next time you see a hermit crab, take a moment to appreciate the wonder that is its anatomy and locomotion. Those ten little legs represent millions of years of evolutionary fine-tuning to produce one of nature’s most delightful creatures.
Coenobita clypeatus Land hermit crabs live close to the shoreline and must have access to both land and water. They are popular pets but do not breed in human care. Consequently, the pet trade harvests them from the wild, which is unsustainable.
A hermit crabs front half is covered with a hard exoskeleton, like that of most other crabs. Its long abdomen has a softer exoskeleton, which can adapt to fit into a spiraled snail shell. A hermit crab contracts its longitudinal muscles to press its abdomen, its fourth and fifth pairs of legs, and the uropods that stick out from the end of its abdomen against the inside wall of its shell.
Its large, left uropod hooks to the center post of the shell. It is used for defense, holding onto tree limbs and balance. Both the smaller right claw and the next pair of clawed appendages are used to bring food and water to the crab’s mouth. Rough surfaces help hold the crab in the shell.
Hermit crabs have reduced gills, and their moist gill chambers have highly vascularized areas for gas exchange. They have stalked eyes with acute vision, and two pairs of antennae. They use the longer pair for feeling and the shorter, feathery pair for smelling and tasting. They also have sensory hairs that are part of the exoskeleton. They use these hairs and their antennae as vibration sensors.
As hermit crabs get bigger, they molt, which means they shed their exoskeletons and grow new, bigger ones to fit their bigger bodies. A crab molts by building up enough water pressure in its body to split its old shell. Some crabs leave their shell and bury themselves in sand to molt. Some species store water in their shells before they molt, and the water stays in the shells during the molt, which can last anywhere from 45 to 120 days.
You can tell that a crab is freshly molted when it has a clean, bluish color. A crab may eat its molted shell, possibly for its calcium, vitamins and minerals.
When selecting a new shell, a hermit crab follows a series of steps:
- Explore the shell visually
- Test the shell for movability
- Explore the shells surface texture
- Explore the external shape of the shell
- Open the shells and see if they are clear. Can the hermit crab get in?
- Check the inside to see if it can handle a snap withdrawal.
- Make sure the shell can stand back up by turning it upside down.
Shemit crabs come in many sizes, from just a few millimeters (less than an inch) long to almost as big as a coconut.
Land hermit crabs live in many different species in tropical parts of the Indo-Pacific, the western Atlantic, and the western Caribbean.
Land hermit crabs live close to the shoreline and must have access to both land and water. They wet their gills and the inside of their shells in pools and cracks in the ocean, and they lay their eggs and spend their early stages in water. Other hermit crab species are entirely aquatic.
Hermit crabs are omnivorous scavengers. They eat whatever they find, although not the former occupants of the shells they use.
At the Smithsonians National Zoo, land hermit crabs are fed crab food and assorted fruits and vegetables.
Hermit crabs mate in seawater. The male holds the female with one claw and taps, strokes, or pulls her back and forth with the other. This is done before mating. Both crabs emerge partially from their shells, placing their stomachs together to mate.
After the eggs hatch, the larvae go through several aquatic life stages and molts. When adulthood is reached, the crabs migrate to shore for a terrestrial life.
Hermit crabs are very popular pets and are easy to find in pet stores, especially ones that are close to the ocean. However, the hermit crab pet business is unsustainable. While people take care of hermit crabs, they don’t breed there. Instead, they go back to the ocean to breed and spend the first part of their lives there. As a result, all hermit crabs purchased through pet shops come from the wild.
Land hermit crabs are also in danger of losing their homes because people are building in and taking over the mangroves and coastal areas where they live.
- Pick your pets carefully, and learn as much as you can about them before bringing them home. Exotic animals don’t always make great pets. Many require special care and live for a long time. Small mammals and reptiles from the tropics are often traded across international borders, and some of them may end up as illegal pets. Animals that have been kept as pets should never be let out into the wild.
- Avoid single-use plastics, such as plastic bottles, bags and utensils. Choosing reusable options instead can help reduce plastic pollution.
- Use fewer pesticides on your garden and lawn to protect nearby waterways. Watershed health can also be improved by not using too much fertilizer, keeping storm drains clean, and picking up after your pet.
- Switch to low-energy appliances, fix leaks, and turn off faucets when not in use to save water.
- Many types of hermit crabs come in different sizes, from less than an inch long to almost as big as a coconut.
- A crab might eat its shell after it has shed, maybe to get calcium, vitamins, and minerals.
- lcLeast Concern
- ntNear Threatened
- vuVulnerable
- enEndangered
- crCritically Endangered
- ewExtinct in the Wild
- exExtinct
- ddData Deficient
- neNot Evaluated