Crabs are one of the most prolific crustaceans in the world and can be found in all the earth’s oceans; in brackish water; in fresh water and some have even taken up residence on land to become terrestrial.
There are approximately 4,500 species of crabs – some are known as true crabs, whilst others are called (as you might well guess) false crabs – creatures that have chosen to become crab like – these oddities include, Hermit crabs, King crabs, Porcelain crabs and the ancient species of Horseshoe crabs, which, by the way, are 450 million years old (wow, these guys have been around a long time!)
Indeed, whilst the lifespan of an average crab is 3-4 years, their species is very old – crab fossils have been found dating back to Jurassic times, with crabs getting into their stride in the Cretaceous period.
Fun fact – a collection of crabs is known as a cast.
Crabs are decapods – which means they have 10 legs, the front two of which are formed into their famous pincers. They often use their legs and pincers to wave and drum to communicate to each other and of course for defence and fighting (which males are fond of when competing for females).
They have eyes on stalks, which they can move around independently (all the better to see you with!!). Although they don’t have teeth around their mouths, some crabs, eg the Brown crab, have teeth in their stomachs to help grind up their food (one remedy against indigestion!)
Crabs have a thick exoskeleton, which protects their soft body parts and they moult many times throughout their development. In fact, shedding their old skin can be a tricky affair, where they must grow a new shell underneath, inflate the old shell with water and spend several painstaking hours extracting every part of themselves from it – failure to achieve this results in no more crab, so it’s vital they get it right.
Female crabs have a rounder abdomen, with a container to carry their eggs, which they do until the eggs hatch. The larvae then swim off into the water to join the plankton colonies, before they grow up into bigger nippers.
Should a crab be unlucky enough to lose a leg, they have the ability to regenerate another – very useful skill. They can move forwards and backwards, but when they want to get a speed on, they move sideways as this is the fastest way for them to travel due to the design of those legs.
On the subject of Horseshoe crabs, did you know that Horseshoe crab blood (which is bright blue) is used in the testing of human vaccines? They have a clever blood cell, which identifies bacterial contagion and this has traditionally been used to ensure that vaccines are free from contamination. However, concerns over the use of the crabs have led scientists to recreate a synthetic molecule in the lab by cloning it from the crab’s blood. This can then be used as a more crab friendly alternative. Indeed, in the current race for Covid 19 vaccinations, Pfizer, for example, have given an undertaking that they will not use crab blood to test their Covid vaccine.
Crabs come in a diversity of colours and sizes. The smallest of which is the aptly named Pea crab, which is just a few millimetres across (1/10 inch) and the largest is the Japanese Spider crab, which can grow up to 4m (13ft) across and weigh up to (31 pounds) – that’s a big crab – but fear not, they are known as gentle giants.
The same can’t be said for Coconut crabs, however, who are only marginally smaller than the Japanese Spider crabs and are known for their voracious appetites. You wouldn’t want to get on the wrong side of those powerful pincers, because they have an extremely strong grip, which is estimated to be about the same as a lion’s bite – ouch! They use these fearsome claws to break into coconuts (they take some cracking!) but they will also eat rats, birds and even their own skin (mmm need some work on the table manners there guys!)
The rarest crab is thought to be the Blue King crab – it’s not totally understood why its numbers are dwindling – it could be over fishing, warming ocean water or increased fish predation. Research is ongoing to try to help increase numbers again, pincers crossed for them!
Rarity isn’t an issue for the most common crab – Carcinus Maenas – known as the shore crab, green crab or European green crab, depending on where you are in the world; and chances are, whatever shore you’re on, you’ll come across one of these crusties. Indeed, they’ve become so invasive that measures are being taken to curb their numbers, such as introducing competing crab species and using them as a food source.
Speaking of food, crabs make up 20% of crustaceans farmed or fished for human consumption, which equates to 1.5 million tons per years. Meat is extracted from hard shelled crab varieties, with soft shelled ones being eaten whole. The most consumed species of crab is the Japanese Blue crab. It’s worth noting that at one time scientists thought crabs did not feel pain; however, more recent research with Hermit crabs suggests the contrary – just a thought before you pick up your fork there.
Whilst there are lots of edible kinds of crabs, some are poisonous. The most toxic of which is the Mosaic crab (found in Singapore) – its shell contains saxitoxin that is 1,000 times more poisonous than cyanide – definitely one to avoid!
As mentioned, there are thousands of species of crabs and amongst their numbers are some rather weird and wonderful varieties:
- Masked crabs – have a shell resembling a human face
- Gaudy Crown crabs – have bright colourful markings
- Arrowhead crabs- have a strange slender body shaped like a guitar with long narrow end like a guitar neck
- Orangutan crabs – have a fluffy orange fur like appearance after their namesake (they use these hairs to catch food from the water)
- Pom Pom or Boxer crabs – have anemones they hold in their front pincers, which they wave at predators and use to catch food
- Shame Faced crabs – cover their faces with their front pincers in a bashful stance (must be shy!)
- Teddy Bear crabs – have hairs all over to resemble the brown fur of a teddy bear (cute!)
- Fiddler crabs – the males have one regular claw and one vastly oversized claw that they use for defence and to beckon females (waving at their girls!)
Crabs – they’re just clawsome! 😊