This is created by froghoppers, of which thier are many different species in the UK. They can be found down among vegetation ready to lay eggs, somewhere close to the ground so that they can overwinter safely. The Froghopper creates a foam nest around the nymphs that provides moisture and protection. This is called cuckoo spit.
Did you know? The adult is a champion jumper and is able to leap 70cm into the air - a greater feat than the flea and similar to a human jumping over a tower block! The initial stages of the jump of the common froghopper are so powerful that a G-force of over 400 gravities is generated; in comparison, an astronaut rocketing into orbit experiences a G-force of 5 gravities. Such amazing force is possible due to the common Froghopper's powerful hind legs.