Squat, brown spider

[Bruce Williams]

Stony Stratford, Bucks.

Help with identification appreciated as always:



Bruce

[aeshna5]

Possibly one of the Xysticus crab spiders.

[Bruce Williams]

Thanks for your help Aeshna5.

Length is ~4.5mm if that helps any.

Bruce

[Geoff F]

There are 12 species which are normally found in the UK but that includes some which are relatively common and others which are rather localised. All are very variable in colouration so I'm afraid that, once again, this requires an expert with a microscope to examine the genitalia.

If you want to play 'guess the spider', then details of the habitat may help to narrow down the most likely suggestions.

X. cristatus is one of the most common and usually has a well defined triangular dark mark on top of the carapace which ends with a clearly defined dark spot. But a couple of other species have slightly similar markings although normally not as large or well defined.

Your specimen however does appear to lack these marks.

X. erraticus tends to be one of the commoner species which occur into the autumn and may be worth a look. But I repeat that these are rather variable in colouration so we are just guessing now.

[frits_b]

Hi Bruce,

That's Ozyptila praticola! One of the more common O. species. It's usually found at ground level.

[Bruce Williams]

Geoff - Thanks for your help - I always appreciate your interest in any of my postings.

Frits - Thank you for your help with identification.

Now I'm guessing from the enlarged pedipalps that this is a male (?). If it is then my estimate of ~4.5mm is clearly wrong. I've checked it again (I use ratio of subject to sensor size) and it measures 4.3mm - still too big for a male. It's just possible that I'd used a 36mm extension tube on that trip and had somehow forgotten to indicate it's use in the folder. If I did use an extension tube then the size would be ~2.8mm.

Bruce

[frits_b]

Originally Posted by Bruce Williams

Now I'm guessing from the enlarged pedipalps that this is a male (?). If it is then my estimate of ~4.5mm is clearly wrong. I've checked it again (I use ratio of subject to sensor size) and it measures 4.3mm - still too big for a male. It's just possible that I'd used a 36mm extension tube on that trip and had somehow forgotten to indicate it's use in the folder. If I did use an extension tube then the size would be ~2.8mm.
Bruce

That (4.3mm) is indeed rather large for this species, 2.8mm sounds more reasonable...

I'm interested in your size measurement method: do you account for focal length, or do you use a prime lens? Do you have a smart way of measuring the size (in pixels) of the spider on the image?
I usually catch my victims to photograph and measure them (with a small ruler), but sometimes I forget to determine their length, and some spiders will simply never sit still, making an alternative method sound attractive.

[Bruce Williams]

Hi Frits,

If I'm on a field trip (also called "walking the dog") I shoot macro with a Nikon D300 + Nikon 105mm Macro VR (and sometimes) + a 36mm Kenko extension tube. I typically shoot 100 to 200 frames per dog walk - the 36mm extension is either on or off for the whole walk.

I always use manual focus and never use a tripod or monopod. I find it comfortable to focus and shoot with either of these two set-ups. I only add more extension rings when I'm shooting subjects in a controlled environment at home.

Unless the subject is too large I always shoot at closest focus. I'm pretty fussy about this and always check the focus ring before taking a series of shots.

I have test shots of a ruler at closest focus with the Nikon 105mm lens alone and with all possible permutations of the three Kenko rings (36mm, 20mm, 12mm).

I store a copy of the appropriate ruler image inside the shoot folder for each day (this is where I must have gone wrong with this pic).

I post process all images in Photoshop and simply overlay (and rotate as necessary) the appropriate ruler image in a semi transparent layer above the subject image. If I add a scale bar (as per many of my Gallery images) I use the ruler layer to construct it.

Here's an illustration I posted on a forum thread back in 2008. It's a different camera (I use the Canon A650 in the winter when the weather is bad) but the principle is the same:



So the moth in the above example is ~7mm long. Please ignore the writing on the ruler image as it relates to another subject.

Bruce

[frits_b]

Hi Bruce,

Thanks for your elaborate reply! That's an interesting approach. I can certainly see its advantages. On the other hand I can imagine it's a bit restrictive to always shoot at closest focus.

That wouldn't work for me presently, because I use a reverser ring to attach my kit lens backwards. I'm constantly zooming in and out to get both pics of the complete animal, as well as detail pictures. This also depends on the behaviour of the spider as it moves about while I'm taking pictures.

But maybe it would be a good idea (for me) to define an arbitrary 'standard' combination of zoom/focus setting and always take a couple of reference pictures to be able to determine the dimensions of the subject. Obviously I'd have to write down which ones are the ref pics. But - I'm brainstorming here - I guess I could also put a small object next to the subject as an indication.

I guess I need to experiment a little. Anyway, thanks a lot for taking the time to illustrate your way of working.

Frits

[Bruce Williams]

I'm guessing that the method works fine for better than 80% of my subjects. If the subject is too large or I can't get near enough to use closest focus then I'll use some other method - if it's necessary (and I remember to do it ). Of course for a lot of common species, whilst precise info on size might be useful it's probably not that critical for identification (ladybirds for example).

Bruce