Post by Jen Berlinghof
The dog days of summer are a bounty for the senses. We see the lemon-yellow of whorled sunflower blooms, taste the ripe flavor of a homegrown tomato, smell the spicy sweetness of bee balm flowers, feel the heat of the day and the cool of the evening. Yet the most quintessential sensation of these end-of-summer days is hearing the overwhelming cacophony of cicada songs around the Lake County Forest Preserves in northern Illinois.
When we talk cicadas, the first questions that often come to mind concern periodical cicadas that emerge en masse every 17 years. This phenomenon is fascinating, but our last emergence of Magicicada occurred in 2007, so we will have to wait until 2024 to experience that spellbinding season again.
The cicadas we hear now, and indeed every summer, are considered annual cicadas. While their lifecycle actually lasts anywhere from two to five years, they’re not synchronized, so we end up hearing and seeing some each year.
Whether periodical or annual, all cicadas go through the same basic lifecycle. A female deposits rice-shaped eggs into grooves on small branches. She makes these grooves with her sharp ovipositor, a sword-like organ that extends from her abdomen for this purpose. Later, teeny cicada nymphs hatch out, then plummet to the ground and burrow in the soil in search of a root to feed on. They start with grass roots, and as they grow and molt, the nymphs eventually work their way up to a host tree root where they’ll sip away at sap for years.
When it’s time to emerge, cicada nymphs claw out of the dirt and head for higher ground to complete one final molt: shedding their exoskeltons. The exoskeletons, or what my kids always called “cicada coats,” remain on tree trunks and tall grasses long after the cicadas’ wings have inflated and they’ve flown away to complete their courtship and mating rituals.
The most obvious of those rituals is the mating songs of the male cicadas. These “true bugs” sing with their tymbal, an organ with a series of ribs that buckle when the cicada flexes its muscle. Like a bendy straw being pushed together and pulled apart, each snap of a rib collectively creates the loud, buzzing song.
And loud it is, sometimes reaching up to 100 decibels, the same intensity as a motorcycle rumbling past on a warm summer night. It may seem strange—and deafening—that a cicada sports exposed eardrums on its abdomen right next to the tymbal. But nature has figured out a workaround; just as male cicadas start to sing, a small muscle folds the eardrum shut.
You might have noticed the cicada chorus isn’t monotonous. It includes a variety of buzzing, clicking, and grinding noises. There are actually more than 190 species and subspecies of annual cicadas throughout North America. In Lake County, we commonly hear three species. The dog-day cicada (Neotibicen canicularis) sounds like a buzzsaw and tends to sing during the heat of the day. The scissor-grinder cicada (Neotibicen pruinosus) sings its grinding song from late morning until dusk. And Linne’s cicada (Neotibicen linnei) sounds like a whirring rattle all day long.
For better or worse, our eardrums don’t fold shut when cicada songs really get going. It’s worth keeping in mind, though, that what may seem like racket to us is sweet music to female cicadas’ ears. Enjoy the crescendo of the chorus in these dog days of summer.