I took a sequence of photographs, unaware of the drama unfolding before me. Only subsequently, in editing images, did I begin to work it out. So here's the sequence.
Stems of grass frame the butterfly. Look closely at those seed-heads on the left. In summer, long stems of grasses are woven into spiders' nests, and traps for the unwary. Watch the position of the butterfly and see how it changes.
The meadow brown alights, showing its rich brown upper-wing surface, facing head down. Follow the grass blade behind the scabious. The butterfly closes its wings, showing the paler underside, and rotates about the flower.
A pale tangle appears above it. I binned this image ( the focus isn't sharp) and retrieved it once I'd realised I was seeing something unusual. Well, everyday for spider and butterfly but I've never seen this before.
I cannot see a spider's web but perhaps the spider was lying in wait in a web. Those grass blades may have been shaped into a trap.