Indiana Ag Connection - Spring Break for Cicadas

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Spring Break for Cicadas - an Event NOT to be Missed
By: Timothy J Gibb, Purdue University - 04/13/2021

Spring break seems to mark a rite of passage into full-blown adulthood for some college-age students. Many feel compelled to experience it at least once before they graduate.

For students, spring breaks can be characterized as an all-out party that occurs after a long winter and most often in a warm, sunny location. Congregations of never-before-introduced peers magically descend on a certain site with nothing but celebrating on their minds. And party they do. Loud, raucous, celebratory parties.

The incessant and insanely loud music, dancing, and festivities that announce this event, 24-7, become mind-numbing, almost deafening for local residents. Neighbors may complain, plead for quiet and even beg authorities to intervene, but nothing will stop the partying. Then, after a few weeks and just as quickly as it started, the noise will abate, celebrations end, and partygoers will vanish. Witnesses will be left to wonder "What just happened?" and, of course, to clean up the litter left in the wake of this strange but unforgettable event.

In the insect world, there is a similar springtime event, also attended by vast numbers of recently transformed adults that mysteriously descend on a common location, where they sing, party and behave in, until then, uncharacteristic ways, oblivious to any local noise ordinances or complaints by permanent residents. Like the student spring break, this bizarre behavioral phenomenon also spans a month or so, while participants try out their newly acquired adult wings and new-found independence.

I am referring to the emergence of the 17-year periodical cicadas, a spectacle that happens but once every 17 years throughout parts of most Eastern and Midwest states. The sudden and highly synchronized mass emergence and gathering of billions of periodical cicadas is a precisely predictable phenomenon that, experienced firsthand, is very memorable for participants and onlookers alike. Then, as with college student spring breaks, all at once the cicadas will be gone; only cast skins and decomposing debris will remain, littering the forest floor, as witnesses are left to marvel at the miraculous event that just happened.

Periodical cicadas, sometimes called locusts, are a marvel of nature in many ways. Adult cicadas have a distinctively stout, robust body with bulging eyes, long transparent wings laced with heavy veins, and fossorial front legs, much like their more commonly seen cousins, the annual cicadas. But periodical cicadas differ by having a comparatively smaller size, a dark (nearly black-brown) body, distinctive, eerie red eyes and orange- or amber-colored wing veins and leg markings.

two cicadas on a branchBehaviorally, they won't be mistaken for annual species due to their famously long lifespan, epic mass emergence and peculiar life cycle. The time between insect egg and adult emergence spans a nearly unprecedented 17 years; some more precocious species have opted for a quicker 13-year interval.

Cicadas begin life as eggs, of course. Each mated female deposits some 500 elongated, cream-colored eggs into a number of carefully prepared incubation chambers made in nearly any deciduous, hardwood forest tree. Females select twigs that have a quarter-inch circumference, measured by grasping them with her front legs. She cuts a small slit in the tender bark, using a large, specialized knife-like ovipositor at the rear of her abdomen, and deposits the eggs.

After several months, eggs hatch and tiny wingless nymphs drop to the ground and begin digging downward, ever deeper into the soil, using their enlarged front fossorial legs. Underground, their behavior and movements are a bit less understood, but we do know that they subsist by finding and sucking sap from the roots of their host trees until it is time for them to become adults.

The predictability of their simultaneous re-emergence is intriguing. How is it that billions and billions of cicadas can all have a life cycle that spans exactly 17 years?

A mysterious internal molecular clock is thought to track the passage of time, calibrated by environmental cues that include the leafing-out of trees and resulting changes in the composition of the xylem fluid on which cicadas feed. The accumulation of 17 such events signals the nymphs to leave the underground soil and roots upon which they have been nursing for more than 200 months and dig themselves up to within inches of the soil surface, where they wait for yet one more environmental cue -- soil temperature to reach 65Â°F.

That temperature is like a green light, triggering the mass emergence race. The nymphs quickly dig out of the soil, find a tree trunk, sign or fence post or any vertical structure upon which to climb a few feet and break out of their shell-like skin (exuviae) only to discover that they are now full, adult-stage cicadas, complete with wings and deafening noise-producing organs (tymbals) on each side of their abdomens.

Intoxicated with their new-found adulthood, and eager to try out both brand new wings and voices, they fly to sunny spots in the upper treetops and join the all-inclusive and infamous choir practice. All this within just an hour.

Male cicadas instinctively know how to use specialized muscles to bend and buckle the heavily ribbed membranes of the tymbal in a unique way to produce the exceptionally loud (ear-piercing, even) shriek or scream that is unique to the cicada.

Entomologists who practice the somewhat suspect avocation of cicada eavesdropping have concluded that at least three songs are broadcasted. Translated into English, the lyrics of the first is said to be a general congregational call for all cicadas to "come, join the party." Then comes a song especially requesting "all females to come closer," and finally an even more personal, seductive, mating invitation, to lure a specific female. (Exactly how these entomologists go about interpreting such songs is not discussed in public and nobody is bold enough to ask.)

Imagine the forest cacophony produced by the simultaneous shrieking and screaming of several million, newly minted, male cicadas per acre, each vying to outdo the next. After 17 years of being stuck in underground isolation cells, suddenly discovering not only very effective high-amplitude, noise-producing voices but an equal number of very interested and carefully tuned-in females to impress creates an energy-packed, eardrum-piercing choral symphony that sears the memory of those who hear it.

The combined chorus is chaotic as well as deafening, and the event is so radical that it can be heard for miles around. This most singular event will be remembered and talked about in the same context as witnessing a full lunar or solar eclipse, Halley's comet, or the moon landing. People in the know will travel miles to hear it in person. Eyewitnesses will remember exactly where they were and mark time by it, just as they remember where they were when the Berlin Wall came down. If truly experienced, it will form lasting memories and lives will be measured by it. Babies may even be named after it. It will be that defining. It has been for me.

As proof I can tell you that I have had several registered quarter horses that go by barnyard names, including Mischief, Chaos, Mayhem, and Trouble. I have to go back to their breed registry records to remember their exact ages, registered names and the dates when each was foaled -- with one exception. Trouble was registered in spring 2004. I also know that he will be 17 years old come May 27, 2021. I know all of that off the top of my head because his full registered name is Cicada's Trouble, and he was foaled during the last major periodical cicada emergence (brood X) in the Midwest. That event sticks in my memory even though it occurred 17 years ago.

You too can have that kind of a life-altering experience, but you need to plan for it now. The Department of Entomology at Purdue University is poised and ready to help. Our Purdue Cicada website will provide a host of cicada-related news stories, bulletins, activities, biological facts and educational ideas to assist. Joining our e-mail list will keep you informed about cicada-related activities at the Virtual Bug Bowl on April 12 and a cicada-themed Bioblitz/Cicada Fest, May 1-9, as well as a running update of times and locations where you can experience cicada mass emergences as they occur throughout the region.

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