We all see these frothy bits of stuff on plants in our gardens and almost everywhere we go where there is plant matter. These are the shelters of spittlebug nymphs. Since remaining moist is important for their development, the secretion fulfills this purpose, and also hides them from predators. There can be anywhere from one to several nymphs in these 'cases'. The spittle is constantly renewed until the nymphs transform into adults.