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.
Spiderlings emerging from egg sac top to the right of centre, female can be partly seen in shadow at bottom, just to the left of centre. She is facing left. Her left band and a few legs can be seen.
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.
Spiderlings continue to emerge.
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.
Forming a disc facing the sun.
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.