spittlebug

A "spittlebug" (immature froghopper) from the superfamily Cercopoidea, a group of Hemipteran insects. These families are best known for the nymph stage, which produces a cover of frothed-up plant sap resembling spit; the nymphs are therefore commonly known as spittlebugs, or spit bugs, and their froth as cuckoo spit, frog spit or snake spit. The froth serves a number of purposes. It hides the nymph from the view of predators and parasites, it insulates against heat and cold, thus providing thermal control and also moisture control. Without the froth the bug would quickly dry up. The nymphs pierce plants and suck sap causing damage, and much of the excess filtered fluids go into the production of the froth, which has an acrid taste, deterring predators. A few species are serious agricultural pests. http://en.wikipedia.org/wiki/Froghopper