What's going on here.......?

Whilst in the Conservation Area today I went in the search of more wildlife, and heard a Sedge Warbler and a Whitethroat singing away in the sunshine. This ups the total of warblers down there now as we have had Chiffchaff and Blackcap already. Fingers crossed for Willow Warbler and Reed Warbler in the near future.
I was looking at all the nettles that need strimming and I came across these..........

..........if you look closely you can see a load of small caterpillars on a fine silk like web. Any guesses as to what they are?? Hopefully in a few weeks we will see lots of what these turn into!!

Nettles are good and bad for wildlife, as you can see they are key to certain species but they can over-run an area so I will be strimming most of them but keeping some micro-habitats of them for particular wildlife.