Can Crabs Swim? The Full Guide

Crabs are short-tailed animals that belong to the family Crustacean and order Decapoda; they are sea creatures that possess five pairs of legs and a flat round body covered in shells. They also have large claws on their front legs.

 As a result, you might wonder whether or not these animals can swim. We have taken out time to answer this question in this article.

Do crabs swim? No, not all crabs can swim. Although they are amphibious animals and can move around in the water, only a few crab species can swim. Most of them move around by walking or running through the ocean floor. Species like the blue crab which can be found on the Atlantic coast, use their rear legs which are shaped like paddles, to swim.

What features give some crabs swimming abilities?

Crabs have ten pairs of legs with the foremost ones being claws. Crabs who belong to the family Portunidae, have special back legs called swimmerets. Crabs that swim have flattened back legs suitable for swimming, just like flying crabs.

These paddle-shaped legs move at a rate of 20 to 40 steps per minute which aids the crab to move ahead during swimming.

Some crabs can walk sideways only. The spider crabs found in British waters are among the few that can walk backwards or forward. Stone crabs can run or walk at the bottom of the ocean.

Why do crabs swim?

Scientists believe that swimming helps crabs to move to close-by areas. Also, swimming helps the crab get past hurdles that they may not be able to climb. It also aids in fleeing from predators or moving away from areas with low oxygen content.

Which family of crabs are known as swimming crabs? 

Portunids are known as swimming crabs. Their legs are modified at the rear. These rear legs are flat and are shaped like paddles appendages. They are called swimmerets seeing that they aid crabs in swimming. These animals usually swim sideways, but can also swim forward and backward occasionally.

Crabs have streamlined bodies which is ideal for fast swimming. They have a hard outer covering, called a carapace, which is flat and broad.

The crab has large pincers that have spines. This aids in catching prey when moving fast. Even though some crabs can swim, they spend a lot of time on the floor of the sea. They are usually between rocks, seagrass, or floating objects.

Crabs are opportunistic regarding their feeding habits. They eat whatever is available at the moment. This includes living organisms, decaying matter, etc. The crabs commonly found in most cuisine belong to this family.

Do crabs swim upside down?

A species of crabs known as the horseshoe crabs are known to swim upside down. They swim at an angle of about 30 degrees with the bottom. This is hardly spotted though. Swimming upside down is beneficial to the crab in multiple ways.

The swimming behavior of the horseshoe crab is believed to be inherited. This is usually learned when they are still embryos lying upside down inside their egg.

Scientists have observed that embryos perform somersaults inside their eggs using their book gills and legs to create needed movement. Newly born larvae can also be seen swimming to the surface.

In what ways do swimming help horseshoe crabs?

Young horseshoe crabs swim in crowded laboratory conditions. It is believed that this is a method of dispersing other animals. The fact that horseshoe crabs are anti-social supports this.

Swimming may also help these crabs avoid cannibalism. These are known to display such behavior under captivity.

Smaller horseshoe crabs use swimming as an alternative method of turning inside water using the help of telson. Sometimes, these crabs move to the bottom of the ocean to regain upright posture.

When horseshoe crabs get bigger, they tend to swim less. Because of this, they are hardly spotted on the surface.

Are blue crabs capable of swimming?

Blue crabs fall under the family of Portunidae and are capable of swimming. Scientifically they are known as Callinectes sapidus which translates as, a beautiful swimmer. 

The blue crab is also known as a decapod which is a reference to its ten appendages.

Out of these appendages, 4 pairs are segmented and the last pair is paddle-like, which aids them in swimming. This feature distinguishes the blue crab from other species as it allows them to swim more freely.

These legs, which are called paddle fins are usually very flexible. They can be easily resolved in a sculling motion to enable the crab to propel itself in water. They can go as fast as 1 meter per second.

Blue crabs are mostly found in saltwater and freshwater regions. However, they are most commonly found in brackish waters, which is a mix of freshwater and saltwater.

These regions possess underwater grasses. Their main sources of food are dead and live fish, snails, sea lettuce, and decaying plants.

Are blue crabs capable of staying out of water for long?

Blue crabs breathe with the aid of gills. They can survive outside water for up to 24 hours as long as they can maintain moisture around their gills. This is why they are usually found in dark, moist, and cool areas to maintain moisture around their gills and to avoid predators.

Crabs have articulating plates surrounding their gill which are used to keep their gills safe and moist.

Most crabs found near the debris line created by a high tide are swimming crabs. Some people refer to them as blue crabs, but this is false.

All swimming crabs belong to the family Portunidae. They have modified legs that are similar to paddles and this helps them swim. Most of these crabs also possess diamond-like bodies and big claws.

What are the survival adaptations of swimming crabs?

Swimming crabs can survive outside water for as long as 24 hours. They can do this with the help of their special gills.

If their gills are kept moist, they can absorb oxygen from the atmosphere. Then they transport the oxygen into their capillaries.

This occurs through osmosis, as the particles move across a permeable membrane to achieve equilibrium on both sides. Once oxygen penetrates the capillary blood vessels, it can transport oxygen throughout the body.

However, their gills must be kept moist for this process to occur successfully. Crabs have anatomical features that work in reducing the evaporation rates from their gills.

What are the growth features of swimming crabs?

Swimming crabs show fast growth. This makes them benthic predators. They are opportunistic and can hunt live creatures if they do not find dead animals to feed on.

During the growth process of the swimming crabs, they renew their exoskeleton occasionally. They re-calcify their body’s exterior to create new shells. They are known as soft shell crabs because of this process. During this, the body of the crab is mostly unprotected and soft. This is immediately after molting takes place.

Note that swimming crabs are the species found in many cuisines worldwide.

Why do swimming crabs wash up on beaches?

Often, swimming crabs can be seen washed up on beaches. There are several reasons for this. Scientists suggest that this is due to the rotting of animal carcasses in the water.

When this occurs, the red tide house bacteria use up most of the oxygen available, then generate anoxic conditions inside the water. Because of this shortage of oxygen in the water, crabs move to land to get the required oxygen. Although, this sometimes results in drying and eventual death.

There are occasions when these crabs are found lifeless on the beach, despite the absence of high tides. This is because of the cold temperatures in the water. Thermoregulation is a tough task for invertebrates. When they find themselves in cold waters, they become lazy and allow themselves to get washed to the beaches.

Do crabs swim in their larval stage?

As the crabs complete their development stage, their mother releases the newly hatched larvae into the ocean.

They become a part of the planktons in the water. They are usually released in the time of tides. They cannot swim but instead move with the water currents. Because of their spines, they stay protected from larger animals.

Crabs are species that can be found in oceans, freshwater sources, and on land. They can move through the water and some species can swim.

Related Questions

Can Crabs Breathe Underwater?

All crabs possess gills that aid in breathing underwater. There are three types of crabs; Semiterrestrial crabs, aquatic crabs, terrestrial crabs. Each capable of living independently of one another. 

Also, if land crabs are submerged for too long they may die of oxygen deprivation because their gills are adapted to air-breathing on land and can no longer derive oxygen.

Can Hermit Crabs Swim?

No, hermit crabs cannot swim. They are land animals. To keep them alive, you must provide drinking water daily. Hermit crabs are not part of the if family; if you immerse submerge them in deep freshwater or saltwater they risk drowning.

Can King Crabs Swim?

No, king crabs cannot swim; they are not members of the swimming crab family. They can only move on the bottom of water bodies with the aid of their long legs while breathing with their gills.

The king crab’s diet majorly consists of fishes, crabs, snails, sand dollars, clams, barnacles, and so on.