Natural History Notes
Spittlebugs Greg de Nevers, 3-24-2000 Revised: Gwen Heistand, 3-25-2005
Mid-March through April is spittlebug time at the Bolinas Lagoon Preserve. Lovely white foam packets appear on the soft, herbaceous stems of the plants that grace the trails of BLP. Remember that the bugs (yes, they’re true bugs) in the middle of the spit are juvenile froghoppers. Our common species of annulate spittlebug is Aphrophora annulata,. Adult froghoppers are seen later in the summer and resemble leafhoppers but they sit frog-like with their head raised and are broader across the middle.
Spittlebugs are phytophagous (a cool word that means they eat plants). These wonderful critters suck plant juice using a fearsome piercing, sucking mouthpart that resembles a needle-like straw which they insert into the soft tissues of plants.
Like I said, spittlebugs are “true bugs,” that is members of the order Homoptera. Like other members of the order they go through gradual metamorphosis. Unlike bees, flies, and beetles, which have complete metamorphosis, the juveniles of froghoppers look like miniature versions of the adults, minus wings. The nymphs shed their skin several times in the process of growing, each time coming closer to looking like an adult. The adults overwinter and produce eggs in March at BLP. There seems to be only one generation each year. Adult froghoppers don’t “spit”. After the last molt, the insect leaves the spittle and moves spittlebug removed from spittle about.
What’s the deal with the spit? It is composed of fluid that is voided from the anus and combined with a mucilaginous secretion from the seventh and eight abdominal segments. The little nymph takes its caudal (posterior) appendages and introduces air bubbles into the fluid. Some accounts say that the bug uses its posterior appendages to whip the fluid into froth (like beating egg whites for meringue). Other accounts say that a double row of plates, on the under side of the soft flexible abdomen, serves as a bellows that blows bubbles of a uniform size. To make each one, the bug reaches its tail up to the surface of the liquid, fills the bellows with air and then, withdrawn, blows out a bubble (like foaming milk for a latte). If you have some time, take the spit off and watch for awhile! The bugs hang head downward so that the spittle flows down over their bodies and covers them. Ask the kids what purpose the think the spittle serves.
adult froghopper
Page 1
Natural History Notes
The foam in which the nymphs live is an adaptation unique to this family of bugs (Aphrophoridae = Cercopidae). The common dogma on the spittle is that the nymphs hide from predators and parasites in the foam. The little foam packs are so white, and so obvious everyone walking the trails of BLP notices them. If parasitic wasps have evolved to insert their ovipositor inches through the bark and wood of a Douglas fir tree to lay eggs on the grubs of wood boring beetles they can’t see, how can a little spittle be effective cover? Another explanation is that the spittle allows the nymphs to be soft bodied without losing moisture. Insects have a terrible problem with drying out, which is usually solved by having a hard, watertight outer coating, the exoskeleton. The hard outer shell means that they have to shed the skin to grow. Spittlebugs have a very soft body which swells slightly between molts (skin shedding events), allowing them to grow between skin shedding events. Essentially, the foam is insulation to protect them from a desiccating (drying) environment. The concept has lately been taken up by fire fighters, who spray foam on buildings to protect them from flames.
What else is amazing about these often maligned but charismatic invertebrates … Adult spittlebugs accelerate from the ground with a force that is 400 times greater than gravity (400g’s). Humans jump with a force that is about 2-3g’s and pass out at about 5 g’s. Until research by Malcolm Burrows was published in 2003, fleas were thought to be the champion jumpers. A 6 mm long spittlebug is able to jump as high as 700 mm with a take-off velocity of 3.1 meters/sec. Think about this. That’s over 100 times its body length and three times as fast as a flea! That’s like me leaping over a 70 story skyscraper without even getting a running start. How do they do this with their puny little hind legs? The muscles in their thorax that power the jump are about 11% of their body weight. The bug locks those puny little legs in place and stores energy in those big muscles. Once there’s enough force generated, the legs are released and away the froghopper goes. Like a catapult. Dr. Burrows used high speed videography at 2000 frames-per-second to capture this. The jump was in just 2 frames! (The picture to left is a leafhopper, not a froghopper, however it gives a sense of the puny legs and incredible leaping motion!) leafhopper leaping
A great spittlebug thing to do with the kids is to have them look for spittlebugs and identify the kind of plant on which they found them. Have one member of the group write a list of all the different species of plants you find spittlebugs on all day long. (Also … how many plant communities do they occur in: oak woodland? grassland? coastal sage scrub? Douglas fir/redwood forest? Coyote brush scrub?). Make a game or contest of seeing who can find spittlebugs on still another species of plant. Try to determine where they occur vertically as well: Do you find them low to the ground? Above your head? At the end of the day you can weave in an ecological concept by asking if spittlebugs are generalist herbivores or host specialists. Contrast the monarch caterpillar and milkweed situation. This game is, of course, a sneaky way of getting kids to care about looking at plants. It uses their natural interest in animals and gross stuff to sucker them into caring about plants. One of the great principles of environmental education: trick them into loving the natural world; they won’t realize they have been hoodwinked until they are on the bus home. Page 2