Nature Notes
by Bob Thomas
The loudest insect in our area is the cicada. It is often erroneously called a locust, but it doesn't hop about as do the grasshoppers and crickets, preferring instead to fly quickly, land, then sit still. Cajuns call them cigale de bois (meaning mosquito hawk of the woods, or cigale de nuit (mosquito hawk of the night).
Our local annual cicadas have rather simple life cycles. Females lay their eggs in tiny slits they cut in twigs with their ovipositor, a sharp appendage at the end of the abdomen. The juvenile stage, called a nymph, reaches the ground when the twig it is in falls or when it loses its grip as it crawls about on the tree. The nymph burrows into the soil and feeds on the juices of roots. When it matures, the nymph exits the ground and climbs the nearest vertical object. This is frequently the same tree were its mother deposited her eggs, but it may be a house wall, garden rake, or a lawn chair. At some point, the nymph stops, its outer skin splits down the back, and it emerges in its adult form. After sitting a spell and allowing its wings to unfurl and harden, it flies away and begins looking for a mate.
It is interesting that, like many other insects, cicadas spend the majority of their lives as nymphs. When they become sexually mature, they have one mission and that is to find a mate. They don't even feed in their adult stage.
The males have organs on the bottom of their thorax (the second section of the body) that produce their love song. The chorus of sounds is a signal for other males to join in and for females to visit and choose a mate. The call of the dominant local species is a loud buzz that increases in intensity then fades away. It may also pulsate in waves of loud buzzing. Each species (there are more than 75 species in the eastern U.S.) has a unique call and it is fun to try to distinguish one from another.
The length of time between egg and adult varies with the species. One of the most widely known is the non-local "17 year locust," but our cicadas are generally three year forms. There are cicadas emerging each year during July and August, so there are basically three breeding populations. Each summer when you hear fresh adults singing, there are one and two year old nymphs in the ground.
If you have cicadas calling in your yard, see if you can find cast skins (called exuvia) of recently transformed nymphs. A tell tale sign that they are around is the presence of perfectly round holes, about the size of a thimble, in the ground from which they emerged.
Also published in Delta Journal, The Times Picayune, September 2, 2007, and August 20, 1989.
A cicada nymph that has just burrowed The nymph clinging to a limb while the
out of the ground and climbed a twig. outer skin splits open and the adult
Note the green body visible through the within begins to emerge.
brown, opaque outer skin. Photo by Craig Hood.
Photo by Craig Hood.
The emerging adult. It is very soft and The newly metamorphosed adult, sitting
vulnerable at this stage. atop its shed nymphal skin. Note the
Photo by Craig Hood. C-shaped, darker green wings on the
side that are not unfurled and far from
functional for flight.
Photo by Craig Hood.
Freshly expanded wings. They expand as The finished product. As the adult sits
the veins are filled with hemolymph (the motionless to avoid predation, the new
"blood" of insects). The cicada is still outer skin hardens, as do the wings.
vulnerable and flightless. When this process is completed, the
Photo by Craig Hood. cicada takes to the wing, mates, and
the cycle begins again.
Photo by Craig Hood.
