The badly photographed frothy mass above is commonly known as Cuckoo spit – found on plant stems it houses a small bright green Froghopper nymph that's feeding on the sap. It produces the froth as a deterrent to predators, a moist hiding place and a good use of excess sap. The adult, below looks fairly similar to the beastie within the froth, but dryer and usually drabber. And it doesn't hide in froth. But it does leap as if shot from a gun when you prod it and resembles a frog somewhat from certain angles – hence the name Froghopper.