A-z - Animals

Crab

Ever wonder why crabs swing their pincers around? They’re using them to communicate and even make drumming sounds with their pincers!

More than 6,700 species of crabs have been identified. Some crabs live only in the ocean, while others live along the shoreline, and still others live in freshwater rather than the saltwater environment of the ocean. Still others live on land full-time, but always near some type of water.

Crabs are very important animals for the environment as they help keep the environment clean. They are also an important food source for a variety of other organisms, including humans.

fun crab facts

Crab
©iStock.com/ANDREYGUDKOV

• Crabs are animals that help the reef survive by removing debris that can kill the reef.

• Crabs have been around since the Jurassic period, more than 200 million years ago.

• Most crabs walk and swim sideways.

• Some species of male crabs fight each other for mates and hiding places.

• Crabs have 10 legs, but the first two are claws, which are not used for walking.



Check out more fun crab facts here: “10 Incredible Crab Facts”.

scientific name

Red Rock Crab (Cancer productus)
©iStock.com/naturediver

Due to the wide variety of crabs, they have thousands of common names such as king crab, horseshoe crab, blue crab, snow crab, coconut crab, etc. However, they all belong to the scientific order Decapodidae, which comes from the Greek words “deka”, meaning ten, and “pous” (poda), meaning feet.

Most of the crabs belong to the family of short-tailed crabs. The term is based on the crab’s characteristic of having a short, hidden tail. The word Brachyura comes from the ancient Greek words for short “brachys” and tail “oura”.

However, not all crabs belong to this family, and some of the better known species, such as the king crab, belong to the stone crab family. The name comes from the Greek word “lithodes,” which means stone-like, because they have a very hard, stone-like shell.

evolution and origin

Gecarcinucidae, Potamidae, Potamonautidae, and Pseudothelhusidae are the four most important families of freshwater crabs whose ancient origins date back to the early Cretaceous period. Most of the current families and superfamilies evolved during the late Cretaceous to early Tertiary.

Their small, protective bodies are more like real crabs, and they move sideways more quickly. Therefore, “crab” is not a legal biological species. These are a group of identically deformed branches of the decapod tree.

The advantages of having a crab shape are still unknown, but according to the researchers, they may be related to the ability to colonize new habitats or diversify into new species.

True crabs were one of the pinnacle forms of crustacean evolution, not appearing until the Cretaceous period (145.5 million to 65.5 million years ago).

Types of crabs

blue crab vs snow crab
©P. Dorman/Shutterstock.com

  • King Crab – King crab is one of the largest crab species, with red king crabs weighing nearly 30 pounds. These crabs inhabit cold climates and are often caught for food production.
  • Blue Crab – The blue crab is another large crab native to the east coast of the United States and the Gulf of Mexico. Easily identifiable by their blue bodies and legs, these crabs have a fifth pair of paddle-like legs that aid in swimming.
  • Bairdi Crab – The Bairdi crab, also known as the Tanner crab, can weigh up to 4 pounds and inhabit the Bering Sea. These crabs have a short tail, a carapace, an abdominal flap, and pincers on the frontmost pair of legs.
  • Hermit Crabs – Hermit crabs have adapted to occupy the hollow shells of molluscs to protect their soft exoskeletons. These crab species have become popular pets with children.
  • Coconut Crab – The coconut crab is the largest land arthropod, weighing up to 9 pounds. Also known as robber crabs or palm thieves, these crabs will eat anything on the ground and are often seen climbing coconut trees to remove fruit or escape from predators.

Here is a complete list of the different crab types:

  • snow crab
  • Chesapeake Blue Crab
  • Dungeness Crab
  • giant mud crab
  • Portunidae
  • fiddler crab
  • florida stone crab
  • ghost crab
  • Cancer
  • hairy crab
  • Tasmanian Cancer
  • big gopher
  • jonah crab
  • spider crab
  • prawns
  • European spider crab
  • frog
  • Japanese hairy crab
  • Chinese Dragon Tooth
  • marmot
  • Goji
  • Heartwood
  • Cancer subfamily
  • flower egg crab
  • Centipede
  • geranium
  • pea crab
  • blue land crab
  • Libya
  • oyster crab
  • blood red half pen
  • red rock crab
  • Southern pheasant
  • hand spider
  • land crab
  • purple crab
  • Flavonoids
  • Cancer family
  • tilefish
  • Sesame
  • Cylindrical subfamily
  • frog family
  • striped shore crab
  • termite
  • Trapezoidal
  • atlantic violinist
  • Wasps
  • Magnolia
  • dog tooth flower
  • Nymphalidae
  • bamboo fish
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appearance

coconut crab
Coconut crabs have a very keen sense of smell, and their sense of smell is different underwater than on land.©iStock.com/Riccardo Maywald

Each crab has a unique appearance that sets it apart from all other crabs, although some look so similar that only an expert can tell them apart. Generally, crabs have a round or oval body, which is sometimes smooth and sometimes covered with protrusions of varying lengths that provide the crab with some protection from predators.

Crabs have ten legs, five on each side of the body. The front pair of legs has evolved into pincers, which the crab can use for defense or to feed itself. In some crabs, the pincers are roughly equal in size, but in other species, such as fiddler crabs, one pincer is much larger than the other.

Crabs come in many sizes. The smallest known crab is the pea crab Pinnotheres pisum, which is only 0.27 inches (0.68 centimeters) in diameter. This is about half the size of an aspirin tablet.

The largest crab is the Japanese spider crab, which can grow up to 13 feet (4 meters) wide when its legs are spread out — about the length of a Volkswagen. The heaviest crab ever found is the king crab, which weighs a staggering 28 pounds, about the same weight as a corgi or miniature poodle.

The crab’s average diameter falls between these two extremes, at just 15.74 inches (40 centimeters) in diameter, about one-tenth the length of a Volkswagen.

A crab’s body is covered with a hard shell called an exoskeleton. This protects the crab for most of its life, but since the exoskeleton cannot grow with the crab, it must be shed, usually once a year, to allow the crab to grow. This is a very vulnerable time for crabs, and they usually try to hide at this time.

A crab’s exoskeleton determines its color. Crabs come in many different colors, depending on the species and where they live. Many are shades of red or blue, but crabs also come in brown, white, yellow, tan, or a combination of colors. The color of the crab can help protect it by providing some camouflage.

However, sometimes the color is very unique, such as the bright red Christmas crab from Christmas Island. In these cases, the color helps the crabs find each other or warn other creatures to stay away.

Crabs can also have smooth shells, or they can be covered with spiny protrusions to deter predators or help them hide in coral reefs or rocky niches.

sexual dimorphism

Crabs frequently express or exhibit pronounced sexual dimorphism. Sexual dimorphism is simply the apparent difference in size, shape, and appearance between the two different sexes of mammals. Males generally have larger claws, a trend that is particularly pronounced among fiddler crabs.

In fiddler crabs, the male actually has one claw much larger than the other, the main purpose of which is to communicate and attract a mate. Another difference is the shape of the abdomen of most male crabs. This is narrow and almost triangular, whereas a female’s belly is more rounded. This is mainly due to where the female crab deposits her fertilized eggs

Crabs - Decapod, - small sand crabs

Behavior

Different species of crabs have different lifestyles. Some crabs are solitary and only meet other crabs when mating. Other types of crabs have been living in large groups called “gypsum”. There can be hundreds or even thousands of crabs in these groups. Living in groups makes it easier for crabs to find a mate, and it also makes it harder for any one crab to be selected as prey by predators, thus helping to keep them safe.

Crabs tend to be shy and usually run away from danger. Although crabs have pincers that can be used to injure a predator, the injury is usually not serious, and most crabs would rather run away than fight. However, some crabs, such as coconut crabs, have pincers large and strong enough to bite off a human finger. These animals live on land and are aggressive. They will even attack small animals such as dogs and cats if encountered.

One type of crab, the horseshoe crab, is not actually a crab at all. In fact, it’s not even a crustacean. This is an ancient species that has changed little since the age of the dinosaurs. People continue to call them crabs because they live in salty and brackish water and behave much like crabs, but they don’t. Surprisingly, their closest relatives are not other crabs, but spiders.

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Habitat

Crabs usually live near water, especially salt or brackish water. They are found in every ocean on earth. Some live in the water all the time, others live near the water, in and between rocks or sand on the shore. Some species of crab live only in fresh water and will die if released into the sea.

Other types of crabs live entirely on land, although most of them live at least partially in water. Typically, they seek out water to breed, where young are born and live in the water until they are developed enough to come ashore. Sometimes land crabs migrate to the ocean in large groups during the breeding season, and like the red Christmas crabs, they seem to take over everything about their lives until the breeding season is over.

diet

What crabs eat varies by species, but most crabs are omnivores, meaning they eat both plants and animals. The tiny pea crab lives as a parasite inside oysters, mussels, sand dollars, sea cucumbers and other organisms, where it consumes plankton brought in by its host to feed itself. Larger crabs live alone and often hide in burrows, where they will rush out to grab shrimp or fish that get too close. Crabs also eat algae, mussels, barnacles, clams, seahorses, and even smaller crabs.

Predators and Threats

Even though crabs have a hard shell that protects them, they are still a favorite food for many animals. Newborn crabs do not have shells and usually live as free-floating plankton, and they are the target of a variety of predators, including small fish, corals, sea anemones, sea worms and the young of most animals.

When crabs begin to grow their shells, they are better protected, but they are still vulnerable to predatory fish, otters, larger crabs, octopuses and humans. Some crab predators use very unique tactics, such as the Pistol Shrimp that “fires” high-powered bubbles that stun the crabs!

The International Union for Conservation of Nature (IUCN) lacks data to classify the conservation status of all crabs, but some species are listed as Near Threatened, meaning their numbers may decline in the future. Some crabs, such as king crabs, appear to be changing their behavior in response to warming water temperatures, which could cause problems with their survival and put them at risk in the future.

Huge numbers of crabs still live in the oceans, and humans take advantage of this abundant resource by catching and eating them in large numbers. Humans consume approximately 1.5 million tons of crabs each year, with Japanese blue crabs topping the consumption list.

Some species may eventually become extinct if crab fishing is not controlled. Regulating the number of crabs caught each season helps keep their numbers in check and ensures their continued presence in the future.

Reproduction, Babies and Longevity

Male crabs usually use their pincers to attract mates. This is especially common in species that have a very large claw or pincer, such as fiddler crabs. Males of some species also fight each other for females, with the winners mating and the losers seeking out another female.

Crabs usually mate when they molt because there is no hard shell to keep them in. This is usually when the water temperature and the outside air are warm. Many aquatic crabs mate belly-to-belly and the eggs are fertilized internally.

A female can store sperm until she needs it, and then use it to fertilize her eggs. The fertilized eggs are placed on her underside, near her tail, and are carried there until they hatch. The larvae swim freely and join the plankton in the water. Even crabs that live on land must migrate to the waters where they were born. Babies must live in water for a period of time before migrating back to land when they become juveniles.

Young crabs molt several times before resembling their parents. As teenagers, they will also begin to behave like their parents, either joining the Crab pack or finding a suitable place to live for themselves. Most crabs live for three to four years, during which time they must avoid predators, find food, molt and reproduce.

population

There are more than 6,700 species of crabs worldwide, and their total population is thought to be large, but the numbers of most species are unknown. Many crabs are listed by ICUN as DD, meaning data deficient, as there is not enough information to tell if they are present in large numbers. Certain types of crabs are threatened because they have limited living areas, and when humans encroach on their territories, crab populations dwindle.

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Humans do keep an eye on certain species because people are interested in the status of species used for food. King crabs, Opilio crabs, Japanese blue crabs and other species that are frequently harvested for human consumption are regulated fisheries in many countries with strict limits on the number, size and sex of the catch. Fishing time is also controlled. This helps keep the population healthy so that there will continue to be plenty of crabs.

human consumption

Crabs have been a part of the human diet for as long as humans have been around bodies of water. Now they are considered exotic and eaten across the globe. Crabs are eaten either whole, just the claws and legs, and in some cultures hard shell crabs are cooked whole. In Southeast Asia, especially those affected by the Infosphere, crabs are cooked with lots of spices and even the roe is eaten.

In the West however, crabs are either steamed and the meat first removed from the shell and served with garlic and butter, or made into crab cakes, a type of crabmeat mixed with egg whites, mayonnaise, biscuit meals, etc. Delicious mixture.

What nutrition does crab meat have?

Are crabs good for your health? Let’s find out.

Nutritional value of crab (100 grams):

  • Calories: Crabmeat contains about 97 calories per 100 grams, which is low compared to many other sources.
  • Protein: Crab meat contains about 38% protein, that is, 19 grams of protein per 100 grams of crab meat.
  • Fat: It contains approximately 2% fat and 0% saturated fat.
  • Cholesterol: Every 100 grams of crab meat contains about 53 mg of cholesterol.
  • Carbohydrates: Crab meat contains no carbohydrates.
  • Vitamins: It contains high levels of vitamins B6 and B12 as well as vitamin C.
  • Minerals: Crab meat contains high amounts of sodium, potassium, iron, calcium, and magnesium.

As you can see, crab can be considered a good source of protein and micronutrients and can be used as a substitute for other meats.

It is worth noting that crab populations have declined dramatically in some areas recently. Crab populations around Alaska, for example, have dropped from about 8 billion in 2018 to 1 billion in 2021. That prompted authorities to cancel the crabbing season around Alaska. While scientists have yet to determine the root cause, rising temperatures around the poles may be responsible for the current situation.

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King Crab vs. Snow Crab: What’s the Difference?

King crab and snow crab are often compared because both species have long legs and a somewhat similar appearance. While the two look similar, they have some important differences, such as king crabs are much larger and they have distinct spikes on their shells.

Almost all crabs are omnivores. They eat algae and other plant matter as well as hunt animal prey.

Crab is good for you because it’s high in protein and low in fat. It also contains nutrients like vitamin B-12 and selenium. Some of the most popular species of crab for human consumption are blue crab, soft shell crab, snow crab, Dungeness crab, stone crab, and king crab.

Some scientists decided in 2005 that crabs don’t feel pain. However, new research on hermit crabs shows that the crabs do respond to electric shocks, suggesting they can feel pain. At this point, it’s not sure if all crabs will be in pain or just some, and if so, how much pain they might be experiencing.

Although crabs can drag forward slowly, they walk sideways because their legs are bent in that direction, which allows them to move faster.

Crabs belong to the animal kingdom.

Crabs belong to the phylum Arthropoda.

Crabs belong to the class Malacostraca.

Crabs belong to the family Crabidae.

Crabs belong to the order Decapod.

Crabs are covered in shells.

Crabs live on coral reefs and shorelines.

Crabs prey on shrimp, fish and mussels.

Crabs have hard armored shells and eight legs.

The average litter size of crabs was 2.

There are 93 different Crab groups.

The scientific name of the crab is Brachyura.

Crabs can live from 1 to 100 years.

Crabs can travel at speeds of up to 12 miles per hour.

Crabs lay eggs.