Study 007

Fen Raft Spider observational study record 007

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

Date:                                                  13.08.2019

Time start:                                       10.30                   

Time finish:                                      12.15

Weather (from BBC weather app):

  • General:                              Sunny intervals and a moderate breeze. Cooler than recently
  • Humidity:                            67%
  • Pressure:                            1016 mb
  • Temp:                                  16C
  • Temp feels like:                16C
  • Wind:                                  14 mph, westerly
  • Cloud cover/sun:              Intermittent sunshine. Cool when the clouds cover the sun

Observational subject:

A number of webs and adults seen today so numbering system devised. Webs numbered 1 to 4  from left to right as seen (South to North), and adults numbered as (=gender + web number): (adult number) eg F2 would be the sole female at web 2, but  F3:1 and F3:2 would be the first and second females seen at Web 3.

Today’s site. The webs look very hard to find in this picture, but with close-focus binoculars on site it’s not so hard.

Vegetation/macro location:

All webs on water solder and in the channel of the dyke


Web 1: Old, empty egg sac and spiderling exuviae present, no adult nearby

The empty egg sac is near the bottom of the web.

Web 2: Spiderlings present, one female seen behind. Not banded, very dark in colour, with white hazy appearance on abdomen, cephalothorax and parts of legs.

Web 2 -the dark female is above, behind and to the left, slightly out of focus

Dark female

Web 3: Old web with empty egg sac, two adult females (F3:1 and F3:2) beneath web, both banded and carrying egg sacs. 3:1 has white markings on back of abdomen and cephalothorax and is tan in colour, 3:2 is dark and has distinctively patterned confluent white patches on back of abdomen and cephalothorax.

Old web with two egg-sac carrying females beneath
Distinctively patterned banded females carrying egg sacs

F3:2 with a clear view of her eyes, which are glinting in reflected sunlight, and her disctinctive white dorsal markings.

Web 3a: Behind and to right of Web 3. Spiderlings present.

Web 4: Spiderlings present. Unbanded brown female beneath web.

The web is above and right of the spider. A few spiderlings are visible

Web 4a: Behind and to left of Web 4. Spiderlings present though hard to see initially.

10.50: F2 moved away from web and disappeared from view for a while, then reappeared later on.

11.00: Spiderlings in Web 2 began to make dish formation facing the sunlight during the study period.

Dishing of spiderlings causing increased sunlight exposure

11.00: F3:1 moved away from web and disappears under water soldier leaf

11.40: F3:1 has reappeared about 50cm to left of previous position

11.50. Spiderlings in Web 2 becoming quite active. No sign of female with hazy abdomen and thorax. She has wandered off again.

Footnote: I asked Dr Helen Smith for her advice on the white markings on the females. This is her response. Utterly fascinating:

“The white staining on the bodies of the adult females only happens this time on year, and (I’m pretty sure) only occurs on females that have second broods and are wearing out. It’s a surface deposit and I’m pretty sure it’s excreted guanine. When they go underwater they excrete a white cloud of guanine to ‘cover their tracks’ against attack by visual predators. When they’re young, they groom their body hair assiduously to maintain waterproofing but at this stage in life they neglect this. You may also have noticed that they are now much more likely to be seen sitting up in quite vulnerable positions guarding the nursery. I suspect they can afford to risk all at a stage when they’re no longer in the market for any further reproduction – and there’s also no advantage in spending time down on the water finding food.”

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