Crabs often get a bad rep (thanks to a certain medical issue). But we think, once you dig a little deeper, you'll be pleasantly surprised by the abilities and agility of these decapod crustaceans. From their sideways walk to their propensity to regrow limbs, when needed, crabs play a vital role in marine ecosystems. Don't get us started on the various types too (6,800 species to be exact). So, if you want to learn more about these multi-limbed marvels, read on to discover our top ten crab facts...
How many types of crabs are there?
The crab family is big - 6,800 various species, big. They're a diverse group of crustaceans belonging to the order Decapoda, which also includes lobsters, shrimp and crayfish. Some reckon the number is actually higher, topping more than 7,000, but what marine biologists can agree on is that they are split between 100 families that range in size, colour, habitat and, most importantly, attitude.
Various sizes
As you can imagine, having so many crabs results in a delightful array of sizes shapes and colours. The Japanese spider crab (Macrocheira kaempferi) is the largest, measuring about 12ft between its claws and weighing up to 42lb. On the other end of the spectrum, you have the pea crab (pinnothera faba) a miniature marvel that is only 0.27-0.47 inches long.
Sideways scuttle
No crab fact file would be complete without the obvious - they walk and swim sideways. Their sideways scuttle results from their anatomy, which hinges the joints of their eight legs (two claws at the front for munching food) to the side. So, while they can move forwards and backwards, it's easier for them to move sideways as each leg moves in a plane that is roughly perpendicular to the crab's body.
Character by the bucketful
The crab family is diverse - it would have to be when there are over 6,000 varieties. Some of our personal favourite are: the pom-pom crab (lybia tessellata) - these crab crabs carry sea anemones in their claws, waving them like pom-poms - the decorator crabs (cryptodromiopsis antillensis), who get their name from their love of decorating as they cover their shells with bits of algae, sponges and other materials, effectively camouflaging themselves, and the coconut crab (birgus latro), known for their incredible strength that allows them to crack open coconuts with their shells. They've also been known to steal shiny objects from people. Who can blame them?
Communication
Another wonderful fact about crabs is how they communicate with one another. They often work together to find food, protect their families and avoid predators. They mainly do this by waving their claws around, especially during territory debates or mating rituals. Some species even drum their claws on their shells to communicate, especially when alerting nearby friends of approaching predators.
Scavengers
Crabs aren't picky. They'll eat pretty much anything, dead or alive, that they can get their claws on. As omnivores, they'll munch on everything from decaying animals to plants, snails and even other crabs. Luckily, if they must crack through another animal's shell, their strong claws come in handy. And once the meal is ready to be consumed, they'll use their claws to pick up the food and pop it into their mouths - not too dissimilar from us really.
Smelling their meal
When finding food, crabs rely purely on their sense of smell to track down their next meal. Through the process of chemoreception (when animals respond to chemical stimuli using their sense of taste and smell), crabs can 'smell' the chemicals that their prey releases into the water and then follow the scent.
All over the ocean
Crabs, such as the blue and Chinese mitten crabs, can be found in all oceans and fresh water. Other species live solely on land, others several miles from water, like the Christmas Island land crab. Species such as the fiddler crab prefer life in burrows, deep in sand or mud, where they stay during winter and high tides. Others, such as the minuscule pea crab, live within the shells of oysters or mussels.
Squatters
One of our favourite crab facts revolves around the hermit crabs' (Paguroidea) habit of using empty snail shells for shelter. They're even known to inspect and line up (Goldilocks eat your heart out) the shells in a social behaviour known as 'shell exchanges'. During these events, the largest crab will take the largest available shell, leaving its old shell for a slightly smaller crab and so on…
Regenerative abilities
Our final crab fact is their ability to regrow lost limbs. Crabs can also intentionally shed a limb through a process called autotomy, which they do when they are threatened (thus helping them escape predators) or if the limb is severely damaged.
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