Study 008

Fen Raft Spider observational study record 008

Location:                                           Carlton Marshes: Dyke 2b, South end, opposite end of 2a

Date:                                                  14.08.2019

Time start:                                        10.00

Time finish:                                      11.30

Weather (from BBC weather app):

  • General:                              Light cloud and a moderate breeze
  • Humidity:                            77%
  • Pressure:                            1014 mb
  • Temp:                                  17C
  • Temp feels like:                18C
  • Wind:                                  14 mph, SSW
  • Cloud cover/sun:              Intermittent sunshine.

Observational subject:

The same webs as Study 007 done yesterday.

Vegetation/macro location:

All the webs are built on water soldier in the channel of the dyke


Web 1: As yesterday: old, empty egg sac and spiderling exuviae present, no adult nearby

Web 2: As yesterday. Spiderlings still present, one female seen behind. Banded, dark in colour, with white hazy appearance on backs of abdomen and thorax and parts of legs. I think this is the same individual as yesterday. She remained partly hidden for most of the study period.

Web 2
The abdomen of the dark female is just visible about 1/4 of the way along the horizontal centre line of the pic, in a gap between two leaves.
Closer up and now in the centre of the pic. You can see several of her legs too. Just a slight shift in angle of view and she’s lost from sight.

Web 3: Old web with empty egg sac, only one adult female with egg sac seen today beneath web. From back markings, identifiable as F3:2 from yesterday, with confluent white patches.

The female is below the left-most quarter of the web, midway between the web and the bottom of the pic.
Great view of F3:2

Web 3a: Behind and to right of Web 3. Spiderlings present and female (without egg sac) seen below web and on water soldier. Hazy appearance to back. Or is this in fact a male? There are “boxing glove” palps. * * * See footnote * * *

Web 4: As yesterday, spiderlings present, no adult seen

Web 4a: Behind and to left of Web 4. As yesterday, spiderlings easier to see today. No adult seen.

Webs 4 and 4a with spiderlings.

No significant movement or activity to report today.


On the difficulty of sexing a Fen Raft Spider -advice from Dr Helen Smith.

” There are a couple of images where you have identified the spiders as males and I wasn’t convinced. Adult males have disproportionately long legs and the cephalothorax always looks relatively bigger than the abdomen. If the palps are curled under, at some angles this makes them looked clubbed. We had issues with this on some images we were sent for the Wildguide to spiders – it could be really difficult to be sure which sex we were looking at. Numbers of adult males around will be very low by now but a bit later in the season we’ll start to see sub-adult males which usually overwinter before their final moult. Their leg and body proportions are ‘female’ and the palps start to become clubbed, although the palpal organ is not fully developed. I’ve only once seen a newly emerged adult male in autumn – at Castle Marshes in mid-October “

Addendum 1:

I returned to these webs 6 days later, after a period of very high winds, storms and rain. Most of the webs were severely degraded though one remained with spiderlings. I took photos but in all honesty they don’t add to what is already in this post. I was unable to make any written notes as I was surrounded by grazing cows -not too bad, until a curious calf approached. Mum was watching and if she had perceived a threat to junior she might have decided to take issue with me. Not keen on dealing with over half a ton of beef charging me, I politely retreated.

Addendum 2:

I returned one more time on the 30th August, 17 days after the start of the study (13th August, Study 007). The area looks desert-like compared with the lush vegetation at the start. Quite a dramatic change in appearance with the water soldiers sinking underwater and very little green, new growth in the channel. There’s evidence of cow damage on the far bank with a new web a metre up in the marginal vegetation empty and probably damaged. Only two of the documented webs in the channel can be seen.

The marshes know winter s approaching. the dykes are starting to change, preparing for their long winter sleep.

3 thoughts on “Study 008

  1. kookie

    Looked up ‘Pedipalps’….. but cannot decide whether they ‘scoffin’ accoutrements’ or ‘previous morphed legs’. Other suggestions are that they ‘get down to business’ with these bits….still they look like they can deliver somewhat a ‘knock-out’ blow!

    1. Doc Doolittle Post author

      Hi Kookie, your last suggestion is in fact the correct one! The males transfer their sperm to these from their primary sex organ, storing it there until they find a receptive female to fertilise. That itself is a risky business and the males stand a chance of being eaten -but will often offer the female a morsel of food to distract her so he can get on with his only role in life without becoming a snack himself. The dangers of dating on the web!


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