Few sounds are more evocative of summer than the pulsating drone of cicadas on a sultry afternoon.
Just one of these bulky, beady-eyed insects makes a lot of noise. A treetop chorus of hundreds of males can seem deafening.
Their high-pitched, raspy singing attracts females, and each type of cicada – there are some 3,000 species worldwide – has its own distinctive song.
The sound comes from two drum-like membranes, one on each side of the cicada’s abdomen. Specialized muscles deform the membranes inward and outward at top speed, and air sacs inside the body amplify the sound.
Cicadas live only a few weeks as adults – just long enough to reproduce – but they spend years underground as immature, wingless nymphs, sucking sap from tree roots via long, beak-like mouthparts.
Once they’re fully-grown and the soil is warm enough, nymphs tunnel upwards through the soil and emerge at night, shedding their old skins. Their large, veiny, transparent wings soon expand and harden. Then the young adults move up into the treetops and the males start singing.
Receptive females don’t join in the chorus, but they welcome males by species-specific flicking motions of their wings.
After mating, each female saws slit-like incisions into twigs and lays hundreds of eggs beneath the bark.
Newly hatched nymphs drop to the ground and begin the long subterranean phase of their life cycle.
Of the 150 or so species of cicadas in the United States, most are “annual” cicadas, with unsynchronized development and the emergence of some adults every year. These are the cicadas we typically encounter in the Lowcountry.
Seven other species in eastern North America, including parts of South Carolina, are “periodical” cicadas, with highly synchronized development and longer life cycles of 13 or 17 years. In periodical species, adults of the same brood in a particular geographical area emerge synchronously in the same year. Population densities during these spectacular mass emergences may reach more than a million cicadas per acre.
Surprisingly, despite some (usually temporary) damage to trees during major outbreak years, cicadas are not considered to be major pests. Also, cicadas don’t bite or sting.
These distinctive insects have figured in the folklore of Provence, Japan and China, and they’ve served as a high-protein, low-fat food in many parts of the world.
Here in the Lowcountry, their loud, insistent hum is a poignant reminder that time is passing and the long days of summer are coming to an end.
Vicky McMillan, a retired biologist formerly at Colgate University,lives on Hilton Head Island. She can be reached at email@example.com.