American Oceans

Interesting Facts About Crabs

Crabs are fascinating creatures that have been around for millions of years.

crabs for arctic terns to catch and eat

With over 7,000 species of crabs found in oceans, rivers, and even on land, these crustaceans have adapted to various environments and developed unique characteristics.

One of the most interesting facts about crabs is that they belong to the decapod family, which means they have ten legs.

Their two front legs are modified into claws, which they use for hunting, defense, and communication.

Crabs also have a hard exoskeleton that protects their body and helps them retain moisture.

Crab Anatomy

Crabs are fascinating creatures with unique anatomical features that help them survive in their aquatic environment.

largest japanese spider crab macrocheira kaempferi underwater


The exoskeleton of a crab is made up of chitin, a tough, semi-transparent material that protects the crab’s body from predators and helps it retain moisture.

The exoskeleton is divided into several segments, including the cephalothorax, which houses the crab’s vital organs, and the abdomen, which contains the gills and reproductive organs.


Crabs have two large claws that they use for defense, hunting, and feeding. The claws are made up of several segments and are powered by strong muscles.

The larger claw, called the crusher claw, is used to crush prey, while the smaller claw, called the cutter claw, is used to tear food apart.


Crabs have ten legs, which are divided into two main groups: the front three pairs of legs are used for feeding and defense, while the back two pairs are used for walking and swimming.

The legs are covered in small hairs that help the crab sense its surroundings and navigate through the water.

Walking Legs

The back two pairs of legs on a crab are called the walking legs. These legs are longer and thinner than the front legs and are used for walking along the ocean floor.

The walking legs are covered in small spines that help the crab grip onto surfaces and climb over obstacles.


In addition to their legs and claws, crabs have several other appendages that serve various functions.

These include their antennae, which are used for sensing their environment, and their mouthparts, which are used for feeding.


Crabs breathe through gills, which are located on the underside of their abdomen. The gills extract oxygen from the water and release carbon dioxide, allowing the crab to breathe underwater.


Like all animals, crabs have a heart that pumps blood throughout their body. However, unlike most animals, a crab’s heart is located in its back and pumps blood through open vessels.


In addition to their gills, crabs also have a pair of lungs that allow them to breathe air when they are out of the water.

The lungs are located inside the crab’s cephalothorax and are connected to the outside world by small openings called spiracles.


Crabs have teeth in their stomachs, which they use to grind up their food before it is passed on to their digestive system.

The teeth are made up of chitin, the same material that makes up their exoskeleton.

Crab Behavior

Crabs are fascinating creatures with a wide range of behaviors.

Blue Crab found under the waters

In this section, we will explore some of the most interesting aspects of crab behavior, including feeding, molting, mating season, migration, defense, camouflage, pheromones, and sound.


Crabs are omnivorous, meaning that they eat both plants and animals.

Some crabs are scavengers, feeding on dead animals and plants, while others are predators, hunting and killing their prey.

Crabs have a variety of feeding adaptations, including sharp claws for grasping and crushing food, and specialized mouthparts for grinding and shredding.


Crabs undergo a process called molting, in which they shed their hard exoskeleton to grow a new, larger one.

During molting, crabs are vulnerable to predators and must hide until their new exoskeleton hardens. Molting is a critical process for crab survival and growth.

Mating Season

Crabs have a complex courtship behavior, with males often fighting for the attention of females.

After copulation, the female can store the male’s sperm for a long time, until an opportune moment to fertilize it.

Some species of crabs have a specific mating season, while others can mate year-round.


Some species of crabs migrate seasonally, moving to different areas to find food, mate, or avoid predators.

For example, the red crab of Christmas Island migrates en masse to the ocean to breed.

Migration can be a dangerous process, as crabs must navigate unfamiliar terrain and avoid predators.


Crabs have a variety of defense mechanisms to protect themselves from predators. Some species have sharp claws for fighting, while others have spines or hard exoskeletons for protection.

Some crabs can also camouflage themselves to blend in with their surroundings.


Crabs use camouflage to hide from predators or sneak up on prey.

Some crabs can change the color of their exoskeleton to match their surroundings, while others have specialized body shapes that help them blend in with rocks or coral.


Crabs use pheromones to communicate with each other, especially during mating season.

Pheromones are chemical signals that can attract or repel other crabs, depending on the situation.


Some species of crabs can produce sounds to communicate with each other or scare off predators.

For example, fiddler crabs use their claws to create a loud snapping sound, while ghost crabs produce a low rumbling sound by rubbing their legs together.

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