Hermit crabs are fascinating little creatures that have captured people’s imaginations for ages. But if you’ve never seen one up close, you may be wondering – what does a hermit crab look like? In this guide, we’ll explore everything about the unique appearance of these charismatic crustaceans.
The Basic Hermit Crab Body Plan
Hermit crabs belong to the crustacean family which includes crabs lobsters, and shrimp. Like all crustaceans, they have a hard exoskeleton, jointed legs, and antennae. Hermit crabs have ten legs – five pairs. The front pair of legs has large claws for defense and feeding.
Hermit crabs come in many sizes, ranging from a tiny 1/4 inch up to the size of a coconut! Most of the 1100+ species are quite small though, between 1 to 3 inches long. Their bodies are asymmetrical, with one claw larger than the other.
A Soft Abdomen Tucked Inside a Shell
The defining feature of hermit crabs is their soft, vulnerable abdomen. Unlike other crabs, hermit crabs cannot fully retract their abdomens into a hard shell. So they borrow empty seashells or other hollow objects to protect this soft part of their bodies.
Their abdomens are specially adapted to clasp onto the inner spiral of snail shells. They use their tail and hindmost legs to secure themselves inside the portable shelter of the shell. Without this borrowed armor they would be easy prey for predators.
Modified Gill Structures
Hermit crabs also have modified gill structures compared to other aquatic crustaceans. Their gills serve a dual purpose – in addition to breathing, they must keep the crab’s abdomen moist. So hermit crab gills have vascularized areas that absorb water.
This adaptation allows hermit crabs to spend time out of water. As long as they periodically dip into water, they can survive on land by keeping the gills and shell interior damp. Some species even reproduce on land near coastal areas.
Stalked Eyes and Antennae
Hermit crabs have stalked eyes that give them excellent vision. Their eyes can rotate 360 degrees for a wide field of view. Two pairs of antennae help the crabs smell, taste, and sense their environment.
A longer pair of antennae detects vibrations and allows the crab to feel around. A shorter pair, covered in sensory hairs, picks up scents and tastes. The antennae help the crabs find food, mates, and shells.
Color and Markings
Hermit crab species exhibit all sorts of colors and patterns. Some are muted and camouflaged in grays, greens, browns or black, while others sport vivid orange or red claws. Some have striking stripes or banding. Color can also indicate a recent molt – newly molted crabs appear bright blue before their new exoskeleton hardens and darkens.
Their hard shells camouflage well on land, and provide warning coloration advertising their claws’ crushing power. But soft or colorful abdomens tucked inside the shells help camouflage in aquatic areas while mating and reproducing.
Important Adaptations
- Asymmetrical body with one large claw
- Ten legs, including large front claws
- Stalked, rotating eyes
- Two pairs of sensing antennae
- Armored front half, soft abdomen
- Modified gills that also absorb water
- Ability to use shells or objects as mobile shelters
So next time you come across a little crab scuttling around with a seashell on its back, you’ll know exactly what a fascinating hermit crab looks like! Their specialized bodies allow them to survive both on land and in water in a portable fortress – one small crab within its adopted mobile home.
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