3 Crabs
There are 60 different species of crabs in the UK and a good few can be found on a first outing to the shore, if you know where to look. Here we will introduce a few very likely finds and where you might find them. You will see what they look like and understand how to separate them from other commonly found crabs.
The species in focus are:
shore crab/cranc gwyrdd (Carcinus maenas)
edible crab/cranc goch (Cancer pagurus)
broad-clawed porcelain crab/cranc porslen (Porcellana platycheles)
You will then be tested.
Three crabs
shore crab/cranc gwyrdd (Carcinus maenas)
©North Wales Wildlife Trust
- carapace wider near eyes than towards tail end
- green, brownish or orange with mottled patches
- when green, claws have colouration of trout together with spots
- five spines either side of eyes
- grows up to 8cm across
- juveniles can be very varied in colour
- live across the shore areas
edible crab/cranc goch (Cancer pagurus) 
©North Wales Wildlife Trust
- reddish-brown, smooth carapace
- oval carapace with piecrust edging
- black tips to chunky claws
- hairy legs
- adults large
- can often be buried in sand
broad-clawed porcelain crab/cranc porslen (Porcellana platycheles)
©North Wales Wildlife Trust
- small crab, up to 1.5cm long carapace
- distinctive, large, flat and very hairy claws
- reduced fourth pair of legs
- found under rocks, in mud and gravel
- often the hairs trap silt, so looks camouflaged
- found mid-low shore
The shore crab can be confused with the velvet swimming crab/cranc llygatgoch (Necora puber), mostly because for adults you don’t get a good look at them, often. They can move quickly, or you might see them in a crevice. So, look for specific differences if you can:
- The shore crab is green/brown-green (orange sometimes) with patterning, but no brown coating
- The velvet swimming crab has bright red eyes
- The velvet swimming crab has a blue tinge and bobbly pale brown patterning (especially seen on its limbs)
- The velvet swimming crab has black tips to the claws
The edible crab can also be confused with a rarer crab species group (Xantho crabs), but which uses similar habitat and buries in the same way. Xantho hydrophilus is also a Climate Change Indicator and is important in its own right. The differences are:
- The edible crab is red-brown (Xantho crabs can be mottled and different colours)
- The Xantho crabs have a carapace which tapers at the tail end, the edible crab adult has an oval carapace
- The Xantho crabs have undulations across the carapace and on the claws making it look muscular like a body-builder.
- The edible crab adult is bigger
Alternative factoids
You’re likely to want to know more about our crabs, as they tend to be very engaging and yet, we still don’t really know enough about their population numbers and distributions. This section will not appear in the quiz as questions.
Many species called crabs are in fact more closely related to lobsters (such as the hermit crab and porcelain crabs).
The shore crab is actually an Invasive Non-Native Species on the East coast of the U.S.
Some crabs, such as the Spiny spider crabs gather together in huge numbers to moult and then mate only once each year. Other crabs will moult several times a year, especially when younger.
The oldest known fossil crab was identified recently (it was found in amber) and is thought to be beyond 100million years old. It pushes back the movement of crabs into freshwater and onto land to the age of the dinosaurs, not the age of mammals.
Many crab species don’t walk sideways at all and many more can walk in all directions, but chose to mostly walk sideways (it’s all down to their muscle attachment).
Most crab species have a slightly larger righthanded claw (crabs can lose and regrow claws with progressive moults, so you might find a left-enlarged claw on a crab).
Many of our volunteers help us at events on shore and we’ve made some brief introductions to our Strandline items (a common feature at our stalls) to help them help us.
For extra information about crabs (not part of the quiz), please do have a watch of a couple of these strandline-on-tour videos (links below).
The next section is the quiz. Click to begin the quiz, the questions will appear below. For the fill-in-the-gaps questions, make sure you spell the same way as the word/phrase in the list, but don’t worry about using capitals or not. If you get any one question wrong within each quiz page, the you will be marked as wrong for the whole page. Answers will appear one you’ve finished each question.
You will be tested on what you’ve learnt so far using the reading and video info. Don’t worry too much, as once you’ve been out on the shore, the ID features you’ve learnt about will make more sense and after a couple of visits you should feel more confident about your ID.
Good luck!