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17-Year Cicadas Emerge in the Eastern U.S.

July 05, 2016

Story at-a-glance

  • Periodical cicadas spend 13 to 17 years underground before emerging as adults
  • Once emerged, they climb trees, shed their exoskeletons, mate and lay eggs
  • Adults live just two to four weeks; the newly hatched nymphs will fall to the ground and burrow under for more than a decade

By Dr. Becker

In ancient China, cicadas were viewed as a symbol of rebirth, as they emerge from the soil each year to turn from young nymphs into adults.1 There are thousands of cicada species and all of them spend a period of years underground before emerging, typically by the masses.

Certain cicada species, like dog-day cicadas, emerge in mid-summer each year (even though individual insects will have spent years underground, their lifecycles are staggered such that some adults appear annually). Others, known as periodical cicadas, disappear for more than a decade at a time.

This group encompasses six species (three that emerge after 17 years and three that spend 13 years below ground). The broods, as they’re called, are identified with Roman numerals.

If you live in parts of Maryland, Ohio, Pennsylvania, Virginia or West Virginia, you may have recently been inundated with the insects; they’re part of Brood V — a generation of bugs that were last seen in 1999.2

If you find the onslaught of cicadas more nightmarish than fascinating, don’t worry — they’re expected to be gone in early July.3

The Mysterious Lifecycle of Periodical Cicadas

Cicadas are among the most mysterious (some might say magical) insects on Earth. Adults live for just two to four weeks, during which they mate and the females lay up to 400 eggs each onto tree branches.

After six to 10 weeks, the eggs hatch and the cicada nymphs, which appear similar to ants, fall to the ground and burrow down about 6 to 18 inches. There they will suck the liquid from plant roots to survive and undergo several life stages before emerging from the ground as adults.

This process may take 13 to 17 years and then, like magic, the insects come up from the ground nearly simultaneously. Exactly what signals them to emerge is unknown, but Gregory Hoover, an ornamental entomologist at Pennsylvania State University, told The New York Times that weather may play a role:4

“A combination of soil temperatures reaching 64 degrees and light rain seems to trigger their ascension, he [Hoover] said. The nymphs climb trees and within an hour, they shed their skins and become adults.”

Cicadas Are Most Known for Their Song

Cicadas have a striking appearance — large bodies, clear membranous wings, and bright-colored eyes — but it’s their song that they’re most known for. “Sung” primarily by males, the sound comes from vibrating membranes, known as tymbals, on the insects’ abdomens.

Some cicada species do not have tymbals and instead use their wings to make crackling noises.

Although you may not be able to distinguish specific songs from a cicada chorus, they’re known to create different types of songs for different purposes, including distress calls, mating and courting calls, synchronized calls among males to attract females and even warm-up songs.5

According to Cicada Mania, which bills cicadas as “the most amazing insects in the world,” cicadas are loud. While a typical chorus may generate the noise equivalent of a noisy cafeteria, holding one up to your ear is the noise equivalent of a loud rock concert or ambulance siren.6

Cicadas Are Not Dangerous

Cicadas are often confused with locusts, although they’re two entirely different insects (cicadas are related to crickets while locusts are a variety of grasshopper). In swarms, locusts can devastate croplands but this is generally not the case with cicadas.

While young trees may be damaged by a large swarm of cicadas, older trees typically come out unscathed. They don’t bite or sting, either, so they pose no risk to humans. If a cicada lands on you and you feel a pinch, Cicada Mania explains what’s likely happening:7

“Technically cicadas don’t bite or sting; they do however pierce and suck. They might try to pierce and suck you, but don’t worry, they aren’t Vampires nor are they malicious or angry — they’re just ignorant and think you’re a tree.

Just remove the cicada from your person, and go about your business. Cicadas also have pointy feet, egg-laying parts (ovipositors) and other sharp parts that might feel like a bite.”

The exoskeleton left behind by cicada nymphs is one of the eeriest parts of a cicada invasion. The empty shells are left clinging to trees or, if the cicada didn’t make it that far, on the ground. In the video below, you can see one boy from Mansfield, Ohio sweeping up the cicadas’ mess, and in the background hear their song.

One caveat: many dogs love to eat cicadas. The bugs themselves are non-toxic (as long as they haven’t been sprayed with chemicals) but do not let your pet consume large amounts of cicada exoskeletons. They’re difficult to digest and may give your dog an upset stomach.

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Sources and References

  • 1 National Geographic, Cicada
  • 2, 4  The New York Times April 27, 2016
  • 3 Cicada Mania, Brood V
  • 5, 6 Cicada Mania, Sounds
  • 7 Cicada Mania June 28, 2008
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