Processionary caterpillar.
I heard about it when researching taking my dog to Brittany, although It dont think it is around the North, mostly South and across Spain.
What I read about it was horrendous! -deadly to dogs if the spines get in tbeir mouth or tongue and very bad for people.
Im thinking of going to somewhere inland from La Rochelle, Cognac area in the Autumn, do they have it around there?