Crab

Crabs are interesting animals that belong to a group of sea creatures called decapods. They have a hard shell that protects them, and their tails are hidden under their bodies. One special thing about crabs is that they can run sideways, and they often hide in rocky places in the ocean.

There are many different kinds of crabs. Some are very small, like the pea crab, which is only a few millimeters wide. Others are very large, like the Japanese spider crab, which can have legs stretching up to 4 meters (13 feet) apart! Crabs eat different things — some eat a mix of plants and animals, some only eat plants, some only eat animals, and a few even live by attaching themselves to other creatures.

People all over the world enjoy eating crabs. In Britain, a dish called dressed crab is a favorite. In places like Goa and Mozambique, people often eat crab curry. Crabs have also been important in stories and art for many years, appearing in myths, paintings, and even as a symbol in astrology. Some people keep hermit crabs as pets, and there is even a funny internet joke that says everything in nature will eventually turn into a crab.

Diversity

Crabs are not a single group of animals. They include the true crabs and many other groups such as hermit crabs, mole crabs, king crabs, and porcelain crabs. Even horseshoe crabs, though they look similar, are actually more related to spiders and scorpions.

Crabs come in many sizes and shapes. The smallest are just a few millimeters wide, like the pea crab. The largest, such as the Japanese spider crab, can have legs stretching over 4 meters. Some crabs live in water, while others live on land or even in freshwater. They eat different things too — some are plant eaters, some eat small animals, and others even live inside other animals and eat what they eat.

Similarity of body plan through carcinisation

Main article: Carcinisation

Most crabs belong to a group called the Brachyura, known as "true crabs", with about 7,000 different types. Other sea creatures, like king crabs and porcelain crabs, look similar to crabs because they have changed over time to have the same shape and habits through a process called carcinisation. This means crabs did not all come from one common ancestor but evolved similar features in different ways.

Many crabs can move quickly sideways, though some walk forward or even swim. The special body shape of crabs includes a flat shell, fused body parts, and a folded tail that hides under their body.

Interactions with humans

See also: Human uses of arthropods

Fisheries and food

Crabs are an important part of the food we eat. About 20% of all sea creatures we catch and eat are crabs, and this adds up to 1.5 million tonnes every year. One kind of crab, called the Asian blue crab, makes up one-fifth of this amount. Other important crabs include several types found in different parts of the world, each giving us more than 20,000 tonnes each year.

In Western Europe, people often eat brown crabs, known for their sweet and delicate taste. The United Kingdom has big fisheries for this crab, especially in Scotland and the South West of England. In North America, blue crabs are caught along the Atlantic coast of the United States and in the Gulf of Mexico. In places like Goa and Mozambique, people enjoy eating crab curry. And in Japan, snow crab meat and eggs are used to make sushi, especially in winter.

In culture

See also: Arthropods in culture

Crabs have been important in stories, art, and myths for a long time. Both the constellation and the astrological sign called Cancer are named after the crab. In Greek stories, there is a tale about a small crab that helped a big monster. Crabs have also been shown in art from ancient times. For example, people in ancient Peru often drew crabs, and famous artists like Albrecht Dürer have painted them too. There are also crab designs in clothes made by people from Panama.

One popular story for children is "The Crab that Played with the Sea" by Rudyard Kipling, where a giant crab causes the tides to move up and down.

As pets

Hermit crabs are often kept as pets and used in fish tanks. One popular kind is the Caribbean hermit crab. They can live for up to 30 years if they have the right home, with sand, coconut fibre, fresh water, and salt water.

Meme

There is a funny joke that says crabs are the "ultimate forms" of life because everything will eventually look like a crab. This joke comes from real science that shows how many sea creatures have evolved to look more like crabs over time. But this process does not happen to humans or other animals.