Spider with large mandibles

[Bruce Williams]

Stony Stratford, Bucks. On fence close to large pond.

Size: See scale bar on pic2.

A very active spider that gave me quite a chase. The mandibles are so large that I initially thought the spider was carrying prey. Help with identification appreciated:





Bruce

[frits_b]

It's a Pachygnatha (Tetragnathidae). I think either P. listeri or P. degeeri. In Holland the spiders of this genus are called 'fatjawed spiders', this is also the literal translation of the latin name. The species mentioned are a bit variable and can resemble eachother.

[Bruce Williams]

Thanks for your help Frits.

You are clearly right with Pachygnatha sp.. From what I can gather three species are found in the UK: P. listeri, P. degeeri and P. clerki. This is obviously a male (elongated chelicera and elaborate pedipalps) I'm guessing you eliminated P. clerki on the basis of size (m=5-6mm) leaving the other two as possibles:

Here's a couple more pics showing size (~3.5mm fully extended) and a closer shot of the pedipalps:



Note: The Collins Field Guide gives: male P. listeri 3-4.5mm and male P. degeeri 2.5-3mm. Is that enough to suggest P. listeri as more likely?



Bruce

[frits_b]

I don't think it's clercki, because the carapace of clercki is much lighter in colour. The other two species can be difficult to tell apart. P. degeeri is much more common than P. listeri, but - as you pointed out - the size of your specimen suggests it's too large for degeeri...

If you still have the spider you could try and take a top view picture of the carapace with lots of light. P. listeri should have a pattern with some contrast on it, while P. degeeri's should be very dark brown or black even.

[Bruce Williams]

These pics were taken in the field so unfortunately I no longer have access to the spider. However I do have a fully dorsal shot and I can say for certain that the carapace is VERY dark with no really noticeable markings.



Bruce