Anyone who has walked through a field of tall grass on a dry day only to find their pants wet has asked the same question: “What gives?”
Chances are, you’ve encountered a population of spittlebugs. Specifically, you’ve just walked through a spittlebug nursery of sorts.
Spittlebugs belong to an order of insects – Hemiptera – whose mouth parts have evolved into a permanent “straw” referred to as a “beak.” They insert that beak into their food and suck out the liquid inside. Some hemipterans are predators and others are parasites, but spittlebugs are exclusively vegetarian. They stick their beaks into plants and suck out the liquid sap (xylem, in this case) inside. The problem is that xylem sap is not especially nutritious, thus these insects must ingest quite a lot of the liquid to survive.
And with so much liquid going in, a lot has to go out, too: Spittlebug babies “drink” plant sap, digest what they can, add certain other components (mucopolysaccharides, proteins and air bubbles), and pass the excess liquid out of their bodies, creating what can only be described as a blob of liquid that looks and feels just like spit.
Larval spittlebugs live inside these spittle masses, happily sucking plant sap and growing up. The spit protects them from drying out (desiccation), being eaten (predation), and having other organisms invade their bodies (parasitism). Once the spittlebugs complete their development and become adults, they leave their saliva-like homes and become free-living insects that jump and fly about, searching for mates.
Some spittlebugs are serious pests of human agriculture and horticulture, causing (in cases of severe infestations) millions of dollars of damage and substantial crop loss. In Central and South America, spittlebugs have significant economic impact as pests of sugarcane and improved pasture grasses; in North Carolina, the two-lined spittlebug (Prosapia bicincta) is a pest of turf grass and some ornamental plants such as holly (Ilex).
In addition to the damage they cause by direct feeding, spittlebugs are vectors for the causal agents of such plant diseases as sugarcane blight, gummosis of peaches, peach yellows and Lucerne dwarf disease. Spittlebugs also may spread a fungus that can cause flagging injury/blight disease of Scots pine, as well as eastern white, jack Japanese, loblolly, mugo, pitch and Virginia pines.
At the N.C. Museum of Natural Sciences, my research focuses on the worldwide diversity and evolution of spittlebugs and their close relatives – amazing insects that include cicadas, treehoppers, leafhoppers and planthoppers. The basic biological information generated through my work can be used by other scientists, now or in the future to investigate improved pest-control methods.
Cryan is deputy museum director, research & collections, at the N.C. Museum of Natural Sciences.