Processionary caterpillars

I believe the local council will spray your trees for you.

Could be wrong of course

Wear gloves, long sleeves and some sort of eye protection. When they are still in the nests, if the nests are low enough, spray the nest with hair spray, as this sticks their hairs (which are the problem) together. Then cut the branch off with long-handled pruners so that the section of branch and the nest can be placed into a plastic bag. Burn the bag in a controlled area - e.g. in a metal bin; or place the nest directly into a bucket full of bleach.

The link below is really useful, IMHO.

https://www.pinardecampoverde.com/ppc.html#:~:text=You%20can%20place%20traps%20around,into%20the%20bag%20suspended%20below.

Hope this helps!