Spittlebug foam, Apostle Islands National Lakeshore, 2014.

This foam is produced by the nymph stage of a froghopper (Cercopoidea) called a spittlebug. They attach themselves to plant stems and hide within the safety of their self-made 'spittle'. This spittle is actually produced from plant juices combined with a waxy ingredient produced by the bug. Air is blown out through a pumplike structure that produces uniformly-sized bubbles in the liquid, creating the frothy appearance you see. This provides a cool, moist environment and protects the spittlebug from predators.