Spittlebugs are also known as frog hoppers. As adults, they are cute, squat, dun coloured insects with spectacular leaping abilities. They really do resemble frogs (with a little imagination).
It’s the nymphs that have the disgusting habit of spitting. Well, it’s actually not spit at all. The foamy slimy ‘spittle’ is a combination of fluid from the insect’s anus, and slimy gunk from glands on the insect’s abdomen. The insect sits head downward on the stem of a plant and exudes the ‘spittle’, letting it pour over its body and cover it completely. The resulting mass keeps the young insect protected from enemies and from drying wind and sun. Gross, but effective.
Like humans, who usually stop blowing bubbles in their milk as adults, spittlebugs leave off spittle production when they grow up. As adults, they use their hopping ability to avoid predators.
Some species of spittlebug can become significant agricultural pests, stunting the growth of herbaceous plants and some forestry trees, but in the home garden, they’re usually not much more than a minor nuisance.