Some Background on Cicadas

Cicadas are insects in the order Homoptera that undergo incomplete metamorphosis.  During complete metamorphosis, an egg hatches into a larva (like a caterpillar, beetle grub, or fly maggot) that later pupates (forms a chrysalis, cocoon, or puparium), and metamorphoses into a very different looking adult (like a butterfly, moth, bee, beetle, or fly).  In incomplete metamorphosis, the egg hatches into a nymph that looks a lot like the adult (you see this in cicadas and also grasshoppers, crickets, and cockroaches).  The last time the growing nymph sheds its skin it becomes sexually mature and develops wings.

Cicada nymphs live underground where they suck on plant roots to get food.  If you look at a dead cicada you can see a long pointed mouthpart like a syringe.  (Live cicadas, by the way, cannot bite and are harmless.) After living underground for a few years (some stay under for as long as 17!), the nymph matures and tunnels up to the surface.  You’ve probably seen holes in your yard where cicadas have popped out.  The nymph crawls along until it gets to a tree, where it climbs up, then emerges from its skin as a sexually mature adult.  With a little effort you should easily find some empty skins in your neighborhood attached to trees and walls.  Adults live for about a month, sucking on plant juices by piercing the thin bark of twigs.

Males make their calls by using special structures called  tymbals.  These flat, ribbed membranes can be pulled in by a muscle until they click.  When the muscle relaxes, the membrane flips back to its original position, making another click (I’m reminded of the pressure lids on some jars that click when you pop them in and out with your thumb).  That’s why all of the calls you hear have a pulsating quality to the song.  The abdomen has hollow cavities that allow the sounds to resonate, and two “tympanum” membranes that vibrate and amplify the sounds.  Each tympanum is covered by a flap called an “operculum” which is important in identification, as you will see later.  The size and shape of the operculum helps modify the sound, as well as contractions of the abdomen that take place as the cicada sings.

The calls of the males attract females.  After mating, the females lay eggs in the bark of limbs or twigs.  The eggs hatch into tiny nymphs that fall to the ground and then burrow downward until they find an acceptable root.  The life cycle then repeats.