An email and attachments from Clive Knight:
“Too late for yesterday’s yellow and black article, I know, but here are a few pics of the wasp spiders I have seen on the reserve this year.”
These are two different female wasp spiders (Argiope bruennichi); if you look closely you can see that the abdominal markings differ. Female wasp spiders build a large orb web low down in the long grass and their main prey seems to be grasshoppers. Like all orb-weavers, they are not poisonous to humans.
The function of the zigzag of white silk (a stabilimentum) in the wasp spider’s web is not clear. There have been several suggestions: the zigzag radiates UV light which attracts insect prey, it makes the web more visible to animals that might inadvertently destroy it, or it makes a blurred and moving spot when the spider shakes her web to warn off intruders.
Here is another post about the reserve’s growing population of wasp spiders.