Cuckoo-spit, spittle bug
Cuckoo-spit is formed by the young of Cercopis sp., Philaenus spumarius and others in the Aphrophoridae family.
The foam hides the nymph, or young bug.
Nymphs can be seen in spring and summer, adults from June to November, eggs overwinter in crack and crevices.
More on cuckoo spit and similar insects