By Dr. Becker
There aren’t many things about cicadas that aren’t oddly fascinating — the noises they make, their life cycle, what the babies eat, how they contribute to the animal world and their sheer numbers. One of the most fantastic and memorable features about cicadas is the cacophony of sound they make. It’s been referred to as “the soundtrack of summer.”
Depending on the type, cicadas in the U.S. can sound like a Geiger counter, a lawn sprinkler or the phone version of fax machine, sometimes with a series of odd clicks, buzzes and whistles sometimes called a “chorus.”
It’s because there are so many cicadas in one place that the noise can be almost overwhelming. In fact, male cicadas in a swarm can produce noise equaling 100 decibels, which The New York Times1 says can be louder than your average diesel train. If you’ve ever been eyeball to eyeball with a cicada, you already know they’re not that attractive, at least from a human standpoint. For male and female cicadas, however, it’s the racket they make that’s so alluring. It’s what perpetuates the species.
The good news is that these little beasts are harmless, and there’s so many in the world that no predator threatens their existence. However, once they do show up, they’re food for whoever wants to eat them. Depending on the variety, they have large wings that seem to drape alongside their green, orange or black bodies, and huge, bulging, side-facing, usually red, but sometimes gray, white, yellow, blue or multi-hued eyes.
One reason their eyes are spaced so far apart is that they have three more tiny, barely detectable eyes known as ocelli (in Latin meaning “small eyes”2). Experts believe they’re used to detect light and darkness.
Cicada Types: ‘Dogday’ and Periodical
A whopping 3,000 species help differentiate cicadas according to their life cycles, which is why they’re placed in two general types.
- There’s the annual cicada, sometimes called “dogday,” as they emerge from their earthen hideouts every year in late summer from the Southwest to the Mid-Atlantic. While some do have multi-year life cycles, overlapping generations make it appear to be an annual event. They’re known for their large wings, green bodies and brown eyes.
- Periodical cicadas, a genus known as Magicicada, arrive, as the name suggests, periodically; either every 13 or 17 years. There are three types of 17-year Magicicadas: Magicicada septendicum, Magicicada cassini and Magicicada septendecula, Cicada Mania3 notes.
Then there are 13-year cicadas: Magicicada tredecim, Magicicada neotredecim, Magicicada tredecassini and Magicicada tredecula. Today I Found Out4 explains:
“Periodical cicadas are separated by broods — a way to categorize the insects based on their life cycle. As of right now, entomologists recognize 30 different broods, but that number can vary as broods die out and new ones emerge. Broods I through XVII are primarily based in the northeastern United States and have life cycles of 17 years. Broods XVIII through XXX live in the southern part of the country and their life cycles are slightly shorter at 13 years.”5
National Geographic reported in 2004 that periodical cicadas (that were then appearing) spend most of their lives burrowed underground, sucking sap from tree roots for food. They then emerge from the ground as nymphs, “transform into adults, do the business of reproduction, and then die.”6
Sometimes the broods overlap, which results in the sometimes dense clouds that have overwhelmed the horizon and attacked unfortunate farmlands. In fact, experts believe cicadas’ immense numbers are a result of the 13- and 17-year life cycles, which are so odd and far apart that they can’t possibly be the ever-present snack predators might decimate if they appeared annually.
How the Cicada Life Cycle Begins
Cicadas begin their existence when their mother deposits them as rice-shaped eggs on plants and tree branches. Actually, the females first dig tiny grooves in the branches using her ovipositor, a wicked-looking thorn-like organ on her underside that also serves to deposit her eggs. Another function for the tiny trench is for the baby cicadas to hide in once they hatch, and that the freshly cut groove releases tree fluids for food.
Once the tiny, white, ant-like baby cicadas have hatched and fed on the tree secretions, they drop to the ground to start their new life underground. They tunnel continuously (which some farmers view as good aeration for the soil) and eat tree sap from the tree roots. They remain there for years, “living in a state of suspended development, waiting for other members of their brood to catch up in growth.”
Depending on whether they crawl out in 13 years or 17 years, cicadas, which are arthropods, climb the tree they started their life in and molt. This is where they shed their exoskeletons (little carcasses often found in trees, wooded areas or on the sides of buildings) and become winged creatures. USA Today explains it succinctly:
“The insect wiggles, cracks the shell down its backside and crawls out of its own skin before spreading transparent wings and taking flight. The process takes about an hour … It’s both gross and strangely enchanting.”7
At first, their skin is white, and the insect itself is quite vulnerable, but soon they literally develop a thick skin. Pretty soon, the singing starts, its purpose being to attract females. As soon as they find each other and mate, the noise dissipates and the male cicadas drop dead, sometimes by the billions, all belonging to the same brood. All this takes place in a matter of a few weeks.
How Do Cicadas Know It’s Time to Come Out?
Cicadas can remain underground as deep as one or even 8 feet in some regions. The specific date-range, Today I Found Out explains, has been based theoretically on soil temperature, but also on growth, depending on the species’ entire life cycle. Underground, nymphs go through five stages of growth; other than the first one, the stages last about four years, depending on a variety of other factors, one being that the rest of their brood needs to catch up. However:
“It was once thought that the secret lay in an internal body clock where they are keeping track of the passage of night and day and the seasons, despite not necessarily having as many direct environmental cues as you find above ground. So even if some groups of them are fully developed early, they still know to wait until the right year based on these environmental cues.”8
Studies conducted at the University of California, though, unearthed information that suggested cicadas emerge, not so much because of cues related to night or day temperature patterns, but the trees they’re eating from.
Scientists used peach trees and “manipulated” them so they’d blossom twice in a year instead of only once. Then they took 15-year-old cicadas and placed them in the soil of the double-blossoming peach trees. The result? After the second flowering, the 17-year cicadas emerged after just 16 years. What the research indicated was that:
“Cicadas seem to keep track of how many springs they’ve been using the tree sap in the roots, which during spring will have an upswing in sugars and the like. When these cicadas detect the 17th upswing, they emerge.”9
Interestingly, in years when an early spring brings blossoms, then a cold snap causes a “second spring,” so to speak, the same phenomenon can occur. If they interpret it as a complete cycle and come out a year early if they’re developed enough, they may even emerge several years early, and can result in a whole new brood.
How Cicadas Sound Has Proved Useful
One of the most often-asked questions regarding these interesting creatures is how one cicada makes such a melodious sound? Science Daily reports research done by the Acoustical Society of America (ASA), which describes the noise made when the insects vibrate in order to emerge from their thin, rattly, plastic-like, corrugated exoskeletons. Their ribbed anatomy helps create the sound when they “deform” their bodies in a Houdini-like process called “buckling:”
“The explanation, in brief, is that a buckling rib is arrested in its rapid motion by impact with the part of the cicada's anatomy called a tymbal, which functions somewhat as a gong being hit by a hammer. It is set into vibration at nearly a single frequency, and the vibration rapidly dies out.”10
In fact, each cicada literally rattles its proverbial ribcage 300 to 400 times a second; thousands of them together reverberate to make a veritable chorus of sound. Simultaneously, female cicadas hear and snap their wings. The males respond by moving closer, at which point the sound becomes softer, which scientists observed is the equivalent of “the cicada putting on its best bedroom voice and uttering the insect equivalent of ‘Hey, baby.’”
Incredibly, research has also been done by the U.S. Navy to see if it might influence the challenge of producing a lot of noise from a relatively small source. In fact, at the Naval Undersea Warfare Center in 2013, the 21st International Congress on Acoustics (ICA) presented its findings on how the cicada's sound could be useful for multiple applications, from ship-to-ship communications underwater, rescue operations and remote sensing.11
Other Little-Known Facts About Cicadas
One problem with the incredible numbers of cicadas that appear when nature says it’s time is that, again, their sheer numbers often damage trees because there are so many cicadas. Tree limbs often break, resulting in damage called flagging.
Cicadas are a “delicacy” in some cultures; “shrimp of the land” is one way marketers have tried to make them appear more tempting. In areas where hunger is rampant, some have suggested taking advantage of the periodical and widespread harvest while it’s available. Dogs and other animals have been known to eat them, which can cause problems that may be immediately apparent, The Atlantic notes:
“Pets can choke on the rigid wings and other hard body parts of the cicadas; pets will gorge themselves on cicadas, and possibly become ill and vomit; pets who consume cicadas sprayed with copious amounts of pesticide can and will die.”12
The entire lifespan of a cicada — of untold thousands of cicadas in one area in some regions — is relatively short, just as their appearance is so very rare. But Science Daily captures the phenomenon well, “As the drowning din of the 17-year brood this summer will remind: we would love them less if they emerged more often.”13