Sand Crab

Last updated: January 6, 2022
Verified by: AZ Animals Staff
Image Credit iStock.com/Pictures-and-Pixels

The sand crab burrows beneath the sand with its tail

Sand Crab Scientific Classification

Kingdom
Animalia
Phylum
Arthropoda
Class
Malacostraca
Order
Decapoda

Read our Complete Guide to Classification of Animals.

Sand Crab Conservation Status


Sand Crab Facts

Prey
Plankton and dinoflagellates
Name Of Young
Larvae
Group Behavior
  • Solitary
Fun Fact
The sand crab burrows beneath the sand with its tail
Estimated Population Size
Unknown
Biggest Threat
Habitat loss
Most Distinctive Feature
The heavy armored shell
Other Name(s)
Mole crab and sand flea
Gestation Period
3-4 months
Litter Size
Up to 45,000 eggs
Habitat
Beaches and dunes
Predators
Fishes and birds
Diet
Omnivore
Type
Crustacean
Common Name
Sand Crab
Location
Worldwide

Sand Crab Physical Characteristics

Color
  • Brown
  • Grey
Skin Type
Exoskeleton
Lifespan
2-3 years
Weight
Less than 1kg (2lbs)
Length
2-5cm (0.75-2in)
Age of Sexual Maturity
1-2 years

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Sand crabs, also known as mole crabs or sand fleas, burrow backward just beneath the surface of sandy beaches to hide from predators and look for prey.

If you happen to be walking along an untouched virgin beach near the ocean, you may notice these unusual animals hidden directly beneath the sand with only their heads sticking out. Sand crabs are completely harmless to people and even entertaining to observe as they move around with the tide. This article will cover some important facts about this animal’s identification, habitat, and diet, including how to catch them and how to cook them.

Sand Crab Scientific Name

Sand crab is a very loose term for a group of crustaceans that burrow beneath the sand. While there are a few closely related families that are referred to as sand crabs, this article will generally focus on the family of Hippidae and more specifically on the genus of Emerita. Ten different species are recognized within this genus. However, sand crabs are not considered to be a “true” crab like the blue crab or the snow crab, but rather a side group that also includes the hermit crab. There are many subtle differences in body shape and anatomy between true crabs and sand crabs, some of which will be covered below.

Sand Crab Appearance

A type of sand crab, a mole crab, with hundreds of egg in the palm of a hand.
A type of sand crab, a mole crab, with hundreds of eggs in the palm of a hand.

iStock.com/jess311

Most sand crabs are small barrel-shaped animals with a tough domed shell, a sharp tail, pointy legs, and multiple pairs of antennae. The shape of the gray-colored body keeps it balanced and camouflaged beneath the shifting sands. Unlike the so-called “true crabs,” however, it does not have any claws on its first pair of legs with the ability to pinch and grasp. Sand crabs are not considered to be giant animals. Males tend to measure less than an inch long, while females can measure up to 2 inches. In some species, the male will actually attach to the leg of the female.

Sand Crab Behavior

Sand crabs spend a great deal of their time burrowed backward beneath the sand with only their eyes and first antennae visible. If disturbed or accidentally displaced from the sand, the crab will tread water by beating their back legs to move around. Unlike many other types of crustaceans, they cannot move in any direction, only backward. While incredible numbers of these animals can be found along the beach, they exhibit solitary behavior and spend most of their time living and feeding alone except during the reproductive season. One of the most interesting facts is that the sand crab tail has the largest known concentration of sensory neurons in the entire animal kingdom.

Sand Crab Habitat

The sand crab is found in beaches and dunes all over the world, including the Atlantic coast of Africa, both coasts of the United States, the Indo-Pacific region, and Australia. These animals live and feed in an area called the swash zone. This is the small stretch of the beach where the breaking waves lap against the shore. As the swash zone moves along the beach in tandem with the tide, the crabs pick up and move as well.

Sand Crab Predators and Threats

Apart from the giant dangers posed by their natural predators, sand crabs are threatened most of all by human disturbances and the loss of habitat caused by coastal development. This can prevent them from easily burrowing beneath the sand. However, they are very common and abundant all around the world. They are not in any danger of disappearing.

What eats the sand crab?

These crabs are preyed upon by numerous types of fish and birds. Several species such as the barred surfperch rely on sand crabs for up to 90% of their diet. The crabs’ main line of dense is, of course, the hard shell and the ability to burrow in the sand. But they’re so effective at attracting predators that fishers will use the soft-shelled stage of the crab as bait.

What does the sand crab eat?

These crabs mostly feed upon plankton and dinoflagellates. These are small, almost microscopic marine organisms that move placidly throughout the water and get eaten by other animals. The crabs rapidly wave their long second pair of feather-like antennae to filter the prey directly from the water. This action occurs so quickly that it’s hard to actually see it.

Because these crabs live in the part of the beach most affected by toxins, their bodies are sometimes filled with domoic acid (a natural byproduct of microscopic algae). When the crabs are eaten by other animals, the toxins are then transmitted further up the food chain. This toxin can have a serious effect on larger animals, including humans. In order to understand how much toxin is present in the water, scientists can measure the amount of toxin in these crabs.

Sand Crab Reproduction and Life Cycle

The crab life cycle varies a bit by species, but the reproductive season usually occurs in the spring and summer months. These crabs have the capacity to create a giant number of young every season. After mating, the female will produce as many as 45,000 eggs at a time and carry them directly on her abdomen. It takes about a month for the eggs to hatch, after which they receive no parental care. As the larvae drift along on the current of the ocean, they can end up a long way from their original place of birth.

These crabs will pass through anywhere between six and 11 different immature stages. Each one of these stages is separated by a molt, during which the larva will shed its exoskeleton and then grow a new one again. The larva can look radically different from the adult stage, almost more like a small swimming marine organism. Depending on the water temperature, the crab will settle down and reach sexual maturity after about a year. They do not have long to reproduce, however. The normal lifespan is between two and three years.

Sand Crab Population

These crab populations are large and robust all over the world based on direct observations. However, the IUCN Red List does not currently classify the conservation status of any of the species. There simply aren’t enough facts known about their population numbers.

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Sand Crab FAQs (Frequently Asked Questions) 

What is a sand crab?

The sand crab is a small crustacean that burrows beneath the surface of the sand where they live and feed. Its anatomy is specially adapted for digging into the sand.

Is the sand crab carnivorous, herbivorous, or omnivorous?

Sand crabs can best be described as omnivorous because they eat a combination of small plant and animal matter present in the water.

Can you eat sand crabs?

While sand crabs are quite edible, you should be aware that their bodies can accumulate toxins from the beach and pass them on to other animals. This can cause significant poisoning in humans. If you still insist on learning how to cook a sand crab, then you should follow a few simple instructions. You will want to rinse it off completely, shake loose any sand or rocks, break off the tail, and squeeze out the insides of the body. It’s not too that different from cooking a typical crab. There are many different recipe ideas you can try when deciding how to cook them, but deep-frying them in the batter after drying them out seems to be a particularly popular type of recipe. You can also simply boil them in hot water. Any type of crab recipe should work.

It isn’t too difficult to learn how to catch these crabs either. In order to expose hidden crabs in the sand, you can actually rake the beach with a simple tool from the store. They should be easy enough to find because they live in great concentrations all over the beach. A simpler alternative method is to drag a net over the surface of the beach while kicking up the sand with your feet. Soft-shelled crabs are preferable to catch over hard-shelled crabs, which can be thrown back into the water. Females are also preferable over males. The identification between the sexes can be determined by their size. Females tend to be larger than males.

What does a sand crab look like?

Identification should be fairly easy. With its feathery antennae, gray-colored domed shell, and lack of claws on the front legs, it looks quite distinct from many other crabs. It also has a pointed tail and back legs to easily burrow backward beneath the sand.

How do I take care of a sand crab?

These crabs are very difficult to care for. They need plenty of sand to burrow in and water that washes over them. They also have a very particular diet. For this reason, they might not make for the best pets.

Do sand crabs bite?

Sand crabs do not have a strong bite. They also lack the claws that would enable them to pinch people.

What do sand crabs eat?

They consume small plankton that passes by in the water.

Are sand crabs dangerous?

Sand crabs are not considered to be dangerous to humans. They don’t really have the ability to pinch or sting.

Can you keep a sand crab as a pet?

It is not recommended to keep one as a pet. Their habitat and diet are very difficult to replicate in an artificial environment. You might want to consider getting a hermit crab instead because they’re generally easier to care for. If you do insist on keeping a sand crab as a pet, however, then you can learn how to catch them with the methods mentioned in the previous section.

Do sand crabs sting?

They do not have the ability to sting at all.

Is sand crab really a crab?

Sand crabs are not considered to be “true” crabs. Instead, they belong to a closely related group called the Anomura crabs (a word which means differently-tailed). Hermit crabs and king crabs are also included in this group. The pincers, tails, and general body shape set them apart from the true crabs. However, the order to which they belong includes all other crabs, lobsters, and shrimp.

Sources
  1. Monterey Bay Aquarium, Available here: https://www.montereybayaquarium.org/animals/animals-a-to-z/sand-crab
  2. Sciencing, Available here: https://sciencing.com/list-animals-found-estuary-8442977.html
  3. Catch & Fillet, Available here: https://catchandfillet.com/atlantic-sand-crab-can-you-eat-how-to-catch/

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