The spit-like substance you see on your grass is actually the foam produced by the spittlebug, a member of the Cercopoidea insect family. Composed of five subfamilies, the group is made up of roughly 2,500 different species that all get their name from their habit of producing spittle that protects them from predators.
Spittlebugs measure from one-tenth of an inch to an inch long and most resemble leafhoppers. Also called froghoppers due to their ability to jump great distances when disturbed, some species exhibit striking colour combinations, such as the common two-lined spittlebug (Prosapia bicincta) that sports a pair of reddish-orange lines across its forewings. Others, such as the meadow spittlebug, found across the United States, are green or yellow as nymphs and tan, black or speckled brown as adults.
As the nymphs, or immature spittlebugs, feed head down on plants, the sap they excrete mixes with air to form foam that eventually encases them. The spittle contains substances secreted by the bugs that thicken and stabilise the foam, making it cling longer to a plant or leaf blade. The nymphs finish their growth cycle wrapped in the foam, and spittle production stops once they reach the adult stage.
Unlike other insects that feed mainly on a plant's phloem, the tissues that transport food from a plant's roots to its leaves, spittlebugs feed on the xylem, tissues that transport water through the plant. Spittlebugs use the large quantities of amino acids found in the xylem for their survival, consuming large amounts of sap to achieve their minimum daily requirement of this important nutrient. Spittlebugs also instinctively feed on plants that manufacture their own nitrogen, such as some grasses and legumes.
The Cercopidae and Aphrophoridae spittlebug families are found in tropical areas worldwide, while members of the Machaerotidae are found only in parts of Africa, Australia and Indonesia. Clastopteridae are found only in the Philippines, and Epipygidae makes its home exclusively in southern Mexico and parts of Central and South America.
Some species of spittlebug cause serious damage to crops such as sugarcane, corn and pasture grasses. Extensive feeding on host plants can result in a weakening of plant stems and leaf petioles. Spittlebug eggs spend the winter in grass stems, in unopened leaves, and in plant debris. On humid days, the nymphs feed low on grass plants, while on hot days, they sometimes move even more deeply into the turf. North Carolina State University reports that spittlebugs have become more problematic in recent years, sucking juices from turf grass to produce their spittle. Grass turns yellow and brown and can be killed if an infestation is severe.