Fen Raft Spider observational study record 009

Location:                                           Carlton Marshes: Dyke 5a, just south of bridge

Date:                                                  23/08/19

Time start:                                        10.00

Time finish:                                      11.15

Weather (from BBC weather app):

• General:                              Sunny and light winds
• Humidity:                            74%
• Pressure:                            1025
• Temp:                                  20C
• Temp feels like:                21C
• Wind:                                  6mph SW
• Cloud cover/sun:              Intermittent cloud, mostly sunny

Observational subject:

One nursery web, one adult, two nearby juveniles

Vegetation/macro location:

Web in channel of dyke, on water soldier. Juveniles on water soldier and frogbit

Observations:

10.00: One nursery web containing spiderlings. A banded adult female is on the far (North) side of web -in deep shade and hard to see initially.

10.20: A little movement amongst spiderlings, which seem to be in two groups. The group on the left begins to spread. There is an egg sac to the right of this group with a group of spiderlings immediately beneath it. The guarding female is behind and to the left of the web. She is in the shade and looks very dark in colour in this light.

Mum was very hard to get a good look at. Moving to a different viewpoint to the left, and knocking up the EV compensation to lighten her up, resulted in a better view of her but with overexposure of the surroundings.

Below is a video of the web showing a burst of spiderling activity. The dark flickering to the left and below the adult female is just the playing of light and shadow in the background. My videography skills are in their infancy so bear with me!

10.21.The banded juvenile just north of the web and facing north, sitting on water soldier leaf. It’s in hunting pose, with forelegs on the water meniscus. Body length is estimated at around 5mm.

10.40 The juvenile on the water soldier has moved behind and up the leaf and is now almost hidden from view.

10.55. A second banded juvenile is seen a metre further away, on a frogbit pad. Body length estimated at 5mm long. The first juvenile has returned to the water surface.

No unusual or notable behaviour was noted today. But it’s worth commenting that the juveniles are relatively close together and look almost identical. There is a good possibility that they are siblings who hatched in this location and are growing up there.

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

Observations:

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 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.

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.

No significant movement or activity to report today.

Footnote:

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.

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.

Vegetation/macro location:

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

Observations:

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

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 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.

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

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

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.

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.”

Fen Raft Spider observational study record 006

 

Location:                                           Carlton Marshes: Dyke 2b (at end where it meets 2a)

Date:                                                  30.07.2019

Time start:                                        11.00

Time finish:                                      12.35

Weather (from BBC weather app):

• General:                  Sunny and a moderate breeze
• Humidity:               59%
• Pressure:                1008 mb
• Temp:                      22C
• Temp feels like:     25C
• Wind:                      17 – 19 mph SSE
• Cloud cover/sun: Intermittent cloud and hot sunshine when present

Observational subject:

A web with ball of spiderlings and egg sac, nearby female adult

Vegetation/macro location:

In middle of dyke on water soldier, 20cm above surface

Observations:

11.00: Spiderlings emerging slowly from egg sac with inferior opening. Female, dark and banded, on water soldier slightly below web and about 20cm from it, and about the same height above water. Sac and spiderling huddle about the same size.

11.40: Female moved down from sedge to water surface. Hard to see as partly hidden by vegetation. Moved back up and onto web itself but continued downwards again and out of sight for rest of study in spite of viewing from a range of angles

12.00: Egg sac now smaller, and ball of spiderlings now about twice the size of the sac.

12.05: Spiderlings appear to have completely emerged from sac and spreading out

12.10: Spiderlings have taken up a concave disc formation, directly facing direction of noonday sun due south.

12.35: No further activity seen. End.

 

It is probably safe to assume that the female had very recently opened the egg sac. If the emergence rate of the spiderlings was roughly constant (making a reasonable assumption) then they would have taken roughly three hours to emerge.

The formation of a concave disc facing the sunlight direction supports the idea that the spiderlings are exhibiting basking behaviour. The female, on the other hand, seemed to have retreated into shade though this could not be confirmed.

Fen Raft Spider observational study record 005

Location:                                           Carlton Marshes: several dykes

Date:                                                  23.7.19

Time start:                                        11.30

Time finish:                                      15.00

Weather (from BBC weather app):

• General:                              Sunny and light winds. Feels hot
• Humidity:                            58%
• Pressure:                            1018 mb
• Temp:                                  22C
• Temp feels like:                25C
• Wind:                                  N 6mph
• Cloud cover/sun:              clear sky

Observational subject:

My aim today was to observe adult spiders. Only 4 days ago on a routine survey we found 38 webs and maybe a dozen adults. Today on a very hot day, circumnavigating most of the survey-allocated Dykes at Carlton across 3 hours,  I saw only maybe 8 of those webs, most looking tattered, and only one adult, in a deeply shaded recess in the margin, under vegetation. Too dark and too distant even for a decent photo.

3 days ago we had storms and brief but torrential downpours. These would have damaged or destroyed many of the webs we had seen on the routine survey. After speaking to a biology graduate friend, I understand that spiders tend to shelter in the cool in hot weather, and are prone to desiccation in such conditions. Maybe the FRS adults had all gone into the shade, or perhaps underwater. There was no sign of guarding adults in the very few webs with spiderlings present that I saw today.

Vegetation/macro location:

N/A

Observations:

It seems reasonable to conclude that the storms followed by hot weather affected my ability to find viable nursery webs and provides explanation for the apparent absence of adults.

I’ve been asked by Dr Helen Smith, the UK’s leading authority on the Fen Raft Spider, to help her answer questions she has about the Fen Raft Spider. Our starting point is observing behaviour. What this means for me is to sit in the blissful peace and tranquillity of Carlton Marshes in a chair, with binoculars, camera and notebook, and simply watch a nursery web and/or and adult spider, and observe, and note. My main job is to report the “how” of Fen Raft Spider behaviour, and where I can, I may make a suggestion or two along the way about the “why”.

The following posts will attempt to be factual and objective reporting, so I’m not attempting to provide a literary read. But some of you may find the information interesting.

Neither of us have any clear idea of where this will lead, or indeed if I’m able to contribute at all to the sum of knowledge around this beautiful and sophisticated animal. But I’m going to have a go!

Thank you for getting this far with me. Please stay on the journey.