Spider with white and brown abdomen

[Bruce Williams]

Stockgrove country Park, Beds. Today (19th December). Size (calculated) 4.75mm.

On fence post between Scots Pine forest and meadows. Help with identification appreciated.



Bruce

[No.9 Spider]

Looks like a Linyphiidae (don't they all almost!). Not one I'm immediately familiar with so rather loathe to guess.
Drapetisca socialis is certainly similar in appearance and according to Dick Jones is found usually on trunks of trees such as Beech and Pines and sometimes on fences in woods.
Only a guess for fun though as I can't say 100%.
It's generally impossible to i.d. with 100% certainty from photo's aside from very obvious ones. Also the Linyphiidae are a huge family, the majority of which are not illustrated in i.d. guides.



No.9 Spider

[Bruce Williams]

Thanks for your help No9.

It certainly does look very much like Drapetisca socialis doesn't it. However my books give a max size of 4mm for this species. To be certain I hadn't miscalculated (not unknown) I went back to my original images and reworked the calculation based upon subject size mapped onto the Nikon D80's 23.6x15.8mm sensor. I still come back to 4.75mm (my macro lens was set to 1:1) - and this would be the minimum subject size.

I take your point about difficulty in getting a 100% id, however do you think the similar looking (but larger) Labulla thoracica might be a possible?

Bruce

[Venger]

My initial response would be Drapetisca socialis, it was the first thing I thought of when I saw the picture (although they're not always right mind, my initial response that is )

[Bruce Williams]

Interesting.

Given Drapetisca socialis is visually such a close fit I decided to test the actual macro being achieved with the D80 + Nikon 105mm Macro VR lens. I manually set the lens to closest focus whenever possible so I took the following pic of a ruler using this same set-up. Here's the result:



As you can see the lens has achieved ~1.07:1 macro not the 1:1 that I had previously assumed.

Applying this latest information shows that the spider must be at least 4.5mm long (excluding pedipalps). Collins gives a size of 3.2-4mm for both male and female. So could this just be an unusually big specimen or does it's size suggest it must be another species?

Bruce

[No.9 Spider]

I personally wouldn't discount a species on a size difference, though in reality I'd have the specimen under the microscope and i.d would not be in question. We are only speculating on possibilities when it comes to attempting photographic i.d.
I've collected Labulla thoracica on many occasions and they have all had dark abdomens so I personally would be doubtful.



No.9 Spider