The nests are processionary caterpillars, be careful of them. If you see them walking nose to tail in a line stay well clear, can really hurt people, can kill dogs. The nests can be dangerous as well if disturbed.
Edit. That sound d a bit grim, they are only dangerous as caterpillars, the moths are totally harmless once they develop. So it's only arround April/ may that you get them in general. So that's a plus. Much love to you all. Happy walks!
I had to google this after reading your comment - I had no idea. Nature is amazing eh.
Lol it didn't sound grim, and you were right to warn us about it.
We also found some black ones at home, and were very cautious about it as they look nasty. Even the cat didn't dare to touch it.
Thanks nonetheless, your concern is much appreciated my friend!