In my experience people leave treating this problem until it is too late.
It is already too late in the life cycle of the chenille processionnaire to treat with [biological/bacteria] Bacillus thuringiensis as the caterpillars are in their 4th stage (setae). they don’t eat as they are getting ready for their mass migration from their cocoons to the earth where they continue their life cycle of pupa to moth. Below is a link to an article with graphic photos of damage these critters can do to your dogs (cats allegedly have more sense and avoid them).
ECOPIEGE FT mesangeverte.pdf (530.4 KB)