Study 009

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


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.

The web is dead centre in the picture

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.

From left to right, guarding female, spiderlings, and egg sac with spiderlings beneath
Closer view

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.

She looks quite different here -the cephalothorax is lighter than the abdomen, and she has light brown bands. The legs are transilluminated in the bright backlighting sunlight -a daylight radiograph!

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.

The banded juvenile is at the meniscus, perched on a water soldier leaf. You can see if just above the frogbit pad at the bottom of the pic, about 3/4 of the way from left to right.
Closer up
Small but perfectly formed hunter. The forelegs are dipping the water meniscus. Tiny vibration-sensitive hairs on the ends of the leg will pick up water movement that could indicate prey nearby.

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.

The second juvenile is on the frogbit pad in the upper left quarter of the pic. The first juvenile is on left of the bottom right quarter, out of focus, on the water soldier leaf.
Second juvenile
First juvenile now in focus, second out of focus.

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.

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