The Spider Crab is well disguised by weed and hydroids.
On the shore (Sussex coast) they will bury completely in the sand under the groynes. They are most likely to be sought out and discovered in June.

 by Peter Glanvill (1992)
 
 

The Spider Crab, Maja squinado, is, without doubt, one of the most distinctive of the British Crustacea. The crab's size and orange spiky shell render it easily identifiable. The sexes can be separated by the huge size of the male's claws which reach a span of 1-5 metres or more.

When in my late teens I was canoeing off the Erme estuary, I noticed large mounds of Spider Crabs near the rocks of Battisborough Island. The mounds consisted of up to a dozen individuals, mainly female. Crabs could be caught by snorkelling down and picking them up. Even though our initial interest was culinary, we noticed that the crabs had obviously feed feeding on the mussel spat carpeting the rocks at that time. Local people informed us that the crabs were gaffed at low spring tide for later eating.

I later discovered the phenomenon was well known but relatively little studied. The crabs' behaviour has even been recorded on film 'Under the Keel' a film by Laurie Emberson on marine life off the Devon coast made a few years ago.

Over the last few years I have kept a note in my diving log when I have encountered the phenomenon and for  those who are interested in seeing it for themselves.

Lyme Bay

The observations were made on the stretch of coast between Burton Bradstock and Seatown. Shingle beaches slope into about 7 metres of water which does not deepen significantly for several hundred metres. The seabed consists mainly of sand with mud patches and low reefs of slabby blue has rock

Crabs can be seen from early July on but their numbers may reflect the sea temperature. In early July 1987 there were many crawling over the Seatown  reef. A few days later at Burton Bradstock many others were seen particular on the mud patches at the seaward side of the reef.  These were mainly females. Male crabs were noted to be fighting and one was seen after seemingly fending off another male, to pick up a female. Another male was noticed carrying a female on its back using its hind claws.

It is worth noting that the reef was covered in a carpet of tiny juvenile mussels.
 
 

In mid July 1990, many moulting  male spider crabs were noticed off Seatown beach mainly near the shore at the junction of sand and reef.

In mid August 1991 at Burton Bradstock many very large freshly moulted male spider crabs were seen on the reef, which was again carpeted in mussel spat. Nine days later I dived at the same site and found the crabs gathered in mounds of 8-10, mainly males. This time I had my camera and was able to record the phenomenon for myself.

Finally an undated observation but which I suspect was late June early July, about 1982, was of hundreds of grapefruit sized female Spider Crabs off Seatown beach  -  all freshly moulted.

What are we to make of this phenomenon? The late moult last year may coincide with the rather bad summer we had. Is moulting encouraged by the presence of food, and do crabs gather at particular sites rather like frogs spawning? Do they breed and moult at the same time? Why, sometimes, are the crabs predominantly female and at others predominantly male?

August 1997.
An extremely large breeding mound of 50,000 Spiny Spider Crab, Maja squinado, was discovered off Burton Bradstock off the Dorset coast. This is an annual breeding site and Peter Glanvill has reported these mounds in earlier years (Glaucus 1992 & 1995). This report of the discovery by Ken Collins at Southampton University made the Times. 

Large rocky area (Lydstep Point) with large numbers of spider crabs (about 4 per sq metre ) and denser in gullies, small caves etc...  I've often seen this kind of thing snorkelling.

However...... I came round the point and across a small sandy bay where there were many swathes of spider crab aggregations.  They weren't piled up in a mound, just a single layer (with the odd one on top of another - but not piled up high).
  They were so dense that I couldn't see the sand underneath them. 

Was this the precursor/aftermath of a mating mound, or an alternative method?

Cheers

Remains of a Spider Crab washed up on the beach in October 2008
Photographs by David & Jacqui Gray

---

 

Katherine Hamblett found the remains of a Spider Crab, Maja squinado on Lancing beach, Sussex, on 20 August 2000.

Reports:

9 November 2007
I went for a long walk on the beach this morning and about 10 :00 am just as the tide was coming in and was amazed by the large amount  of dead and washed up Spiny Spider Crabs, Maja squinado, in one spot I counted 12, I stopped counting at 26 as I walked from Lancing Beach Green towards Onslow Court, Sussex. At one point one crab came washed up and was still alive, the poor thing could hardly move so I picked it up and popped it back into the water. The smallest I saw was about the size of a tennis ball (the carapace) and the largest was the one I threw back at about four tennis balls put in a square. 

6 July 2004
Whilst walking along Gurnard Beach on the Isle of Wight (near Cowes) with my sons we found hundreds of dead Spider Crabs along the shore line washed up with all the seaweed. Originally we thought it was just the shell possibly from a mass moulting but we found whole carcasses with legs and eyes intact. 

1 June 2004
Jan and Katherine Hamblett discovered a large Spiny Spider Crab, Maja squinado, on the sand and rock beach opposite Brooklands Boating Lake, east Worthing, West Sussex at the edge of the sea in a dip on a low spring tide. It was missing two of its legs. 

Mid-July 2002
A Spider crab aggregation at St. Agnes, Cornwall was seen by friends when snorkelling.
And a Spider crab aggregation seen by myself on Sunday last at Seatown, Dorset.
Interestingly they seem to be at the same spot I last saw them ten years ago  i.e. straight out from the car park on the line between the sand and the shingle slope.  Most had recently moulted and were all roughly the same size.
The numbers run into the thousands.  Why they congregate here I don't know.  Just 250 metres down the beach to the west there were none.  Is it something to do with the freshwater that comes down the beach at this point - can they locate it like salmon? 

11 June 2002
The presence of Spiny Spider Crabs, Maja squinado, underneath the wooden groynes on Shoreham beach, West Sussex,(TQ 216 047), south of Weald Dyke (road), is a notable aspect of the wildlife fauna of Shoreham and little known. Although it is the smaller crabs that are found at low tide, these are still the biggest animals found between the tides. 
In captivity, one of the Spiny Spider Crabs moulted twice before 30 June 2002. 

British Marine Life Study Society
BMLSS Rockpooling
Wet Thumb (Marine Aquariology)

3 August 2000
Went to Woolacombe Bay, north Devon. Whilst snorkelling found an area of rocky seabed (low water at about 3 metres) writhing in edible spider crabs which seemed to be moulting. Never seen so many hundreds seen in the murky water, and certainly thousands altogether - quite eerie. Trying to find out a bit about their natural history to see if they 'migrate' to selected areas to moult or have sex. A lot had died too. If you have any info. or ideas, let me know please.
The visibility was not brilliant, but diving down in the small areas between the rocks I would say I saw hundreds - so this could indicate thousands in the surrounding waters.
Location - south corner of Woolacombe Bay, Devon (close in shore to land that leads to Baggy Point. About 100 m of low tide level.
(NB none washed up on shore though at that time).

Best wishes,
Gerald Legg
 

Peter Tinsley (2000)

Gynandromorphy

Dear Rowena:

I sent the following message to the Crust-L list on Saturday and received the reply below.

I received an excited call late last night (Friday night) from a fisherman who found eggs in a large male spider crab, Maja squinado.  The fisherman said the crab had all the external morphological features of a mature male crab... large chelipeds, narrow abdomen etc. He was eating his supper and had eaten the meat from the chelipeds and walking legs when he pulled the thoracic sternum away from the carapace to find eggs on the right side of the body. He has saved the remains of the crab for me.  I will look at it today.
I am not a crustacean biologist so an indication of any morphological features I should look for in the crab would be appreciated.  How common an occurrence is this?
The crab is cooked so is there a value in saving it?
Email:  fishinfo@guernsey.net

Reply from: Cédric d'Udekem d'Acoz [cdudekemda@be.packardbell.org]

Dear Richard,

It is not the first record of gynandromorphism in Maja. Several years ago, two gynandromorphic Maja were found in the area of Dinard, France, Western English Channel. I have seen one of these specimens. It had not a full external male morphology. It had a normal male morphology on one side and a normal female morphology on the other side. His abdomen was therefore totally assymetrical. The specimen was not ovigerous when I saw it.
Apparently, gynandromorphy is less rare in Maja than in other crabs (do not ask me why !). For more informations on the two gynandromorphic French Maja, please contact Pierre Noël for your information, the European Maja squinado sensu lato has recently been splitted in 2 species : Maja brachydactyla Balss, 1922 (Atlantic coasts of Europe) Maja squinado (Herbst, 1788) (Mediterranean)
If you accept this splitting, your specimen should be considered as M.  brachydactyla.
Although cooking has certainly (partly) damaged the internal anatomy of the crab, it would be certainly interesting to preserve it. I think that the best it to put it for some days in formaline 10% and to transfer it later in 70% ethanol.
End of reply
Rowena, it has been too many years since I was at school.  I need a good biological dictionary for all the new (particularly taxonomic/ genetic) terms used.  What does "sensu lato" mean as oppose to "sensu stricto"?  I have seen the term used for phyla and species but I have never understood its meaning.  What do you think of the new species name for the spider crab?  Will you be using it in your book?

Best Wishes,
Richard
Richard Lord
Guernsey GY1 1BQ
Great Britain

Email:  fishinfo@guernsey.net
Tel: +44 (0)1481 700688
Fax: +44 (0)1481 700699

Hello Richard,

I do not think it is particularly unusual as most fishermen (Sussex) have mentioned Spider Crabs which they have been unable to sex.

Cheers

Andy Horton.

There are numerous other rhizocephalan barnacles parasiticising other crustaceans, notably a species called Clistosaccus paguri infecting the Common Hermit Crab, Pagurus bernhardus, the genus Peltogaster infecting other hermit crabs and Drepanorchis neglecta, that infects spider crabs.
Discussion Link
European Rhizocephalan Species List
Discussion Link 2
Discussion Link 3
Sacculina notes (from Crust-L)
Gynandromorphy

Abnormal Lobster (Link)
 
 

A review of the species complex around M. squinado was able to differentiate between specimens from the Mediterranean Sea and those from the Atlantic, and concluded that the Atlantic specimens were a separate species, called Maja brachydactyla Balss, 1922 [10] . The specific epithet squinado derives from the Provençal name for the species — "squinado", "esquinade", "esquinado" or "esquinadoun" — recorded by Rondelet as early as 1554 [6] .  (Wiki)
 

Northern Stone Crab,  Lithodes maja
Photograph by Jim Greenfield

The Northern Stone Crab is a northern species found in the seas around Scotland including this specimen from the seas around St. Abbs Head, south-eastern Scotland. 

The Giant Spider Crab, Macrocheira kaempferi, from deep water in the Pacific Ocean near Japan,  have been recorded with a 35 cm (14") wide body and a claw span of nearly 4 metres (12 ft.). It has got a small body with very long legs. 
 

CRABS OF THE SEASHORE OF THE BRITISH ISLES