By LESLIE BISHOP, guest columnist
Natural phenomena have intrigued humans throughout history. These days, with access to information far and wide, people can plan their year to witness certain events in nature. Some wait for the rare opportunity to witness the “super bloom” of wildflowers in Death Valley, some travel long distances to see a total solar eclipse (how about Antarctica in December 2021?), or others travel to the Serengeti to witness the annual migration of the wildebeests.
Yet as an entomologist, there is no phenomenon quite as amazing as what is about to take place right here in Brown County along with most of the East Coast: the emergence of the periodical cicada.
In Indiana, there are at least 20 species of cicadas. Of these there are two major types of life cycles: annual and periodical.
Annual cicadas, called dog-days cicadas, emerge every year and are the signature sound of summer. These large, green cicadas with big, dark, bulging eyes and black wing veins sing from the trees until early fall. Even though annual cicadas take several years to develop, the generations overlap so that these cicadas emerge every year.
On the other hand, cicada species with the periodical life cycle emerge synchronously after long periods of time. This year in late April or early May, the next emergence of the 17-year cicada — Brood X in the species Magicicada septendecim — will emerge in great numbers. These cicadas have striking black bodies, red eyes and red wing veins. They will fill the air with loud choruses due to sheer numbers of individuals.
There can be as many as 1.5 million cicadas in an acre! But don’t worry! Adult cicadas are not the same as locusts (which are grasshoppers) and will not eat your plants.
Both annual and periodical cicada species share a common cycle. After mating, a female cicada inserts tiny white eggs with her sharp ovipositor into a tree or shrub limb. Once the egg hatches, the small white nymph will begin to feed on the tree fluids.
After several growth stages, or molts, the young nymph will fall to the ground where it will excavate with front legs especially adapted for digging until it finds roots to feed on. The cicada nymph will stay underground, tunneling and feeding on root xylem, from two to 17 years depending on the species.
After the long underground stage, cicada nymphs tunnel up toward the surface to prepare for emergence. This is the first sign to look for as you prepare to witness the emergence this spring — and it is happening now. Just today we found a number of holes in wet soil under the pine trees; many of the holes were covered with golf-ball sized chimneys (see photo).
The cicada nymphs wait in their tunnels until the soil is warm (about 65 degrees Fahrenheit), and then, after a warm rain, they will emerge to climb up the nearest available tree. There, they shed their nymph exoskeleton and unfurl their transparent, crumpled wings.
Once their new wings and exoskeleton hardens, they can begin their brief adult life looking for a mate. The males call, the females respond, they mate, and the life cycle begins again.
Once the males start calling, the cicada chorus can be alarmingly loud. Male cicadas have two chambers on their abdomen covered with membranes (tymbals) that vibrate by contraction and relaxation of muscles to produce sound. One entomologist compared their bodies to guitars with air-filled spaces that act like resonating chambers that will amplify the sound.
Both the male and female cicadas have auditory organs that receive sound. The males produce a species-specific mating call, and only females of the same species will respond to that call. Some calls sound like shaking maracas, others like buzzing chainsaws, and others like pulsating motors. And in a chorus, the males synchronize their calls into a rhythm from a low hum to an impressive crescendo.
Scientists have been intrigued by the ecological effects of periodical cicadas for years. When billions of insects emerge and die, what is the effect of this “resource pulse” in the environment? Studies have shown that the tunneling activity of nymphs aerates the soil and modifies the soil profile. The feeding of nymphs on tree roots has no negative effect on tree growth or reproduction, and the input of the decaying adult bodies provides fertilizer for the trees which actually improves growth. The massive emergence of adult cicadas provides a glut of food for insect predators, and yet in years of emergences, the populations of bird predators are low — an intriguing paradox.
Do the cicadas have a negative effect? Arborists advise fruit tree growers and homeowners not to plant young trees during an emergence, as the egg-laying can damage young vines and branches. Otherwise, they are harmless.
So, be ready Brown County. The cicadas are coming. There will be lots of cicadas, and they will be very loud. But they won’t be here long — only several weeks. Will you join me in the wonder of this natural phenomenon?
Leslie Bishop is a Brown County resident and retired biology professor from Earlham College. She can be reached through the newspaper at [email protected].
