U.S. Prepares for Insect Invasion 17 Years in the Making

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Scientists have not yet agreed as to why some cicadas stay a certain amount of years underground before surfacing to become adults.

Washington — They have been living at least 20 centimeters underground for the past 17 years. This spring billions of cicadas known as Magicicada septendecim will emerge to invade parts of the U.S. East Coast, filling the skies and trees and making a lot of noise.

There are more than 170 species of cicada in North America, and over 2,000 species around the world. Most appear every year, but certain types operate on a 13- or 17-year schedule. This year’s visitors, known as Brood II, were last seen in 1996 and are one of the insect’s largest populations. People living between North Carolina and Connecticut may need to use shovels and rakes to clear them out of the way. Estimates of their eventual number are ranging from 30 billion to 1 trillion.

It may sound like some kind of biblical plague, but the insects are harmless and most people will only be annoyed in trying to avoid them, and by the incessantly loud drone of male cicadas singing in search of a mate. For nature and science lovers, their periodic appearance is actually a very interesting phenomenon.

According to the National Geographic Society, researchers have theorized that cicadas following a 13- or 17-year life cycle have evolved to follow this schedule to make it difficult for predators such as birds and squirrels to anticipate when they will emerge from the ground to molt into adult bodies and reproduce.

Another theory suggests that their life cycles evolved during the Pleistocene Epoch, which began 2.6 million years ago and lasted until around 12,000 years ago. That era was characterized by dramatic temperature fluctuations, and the insect could have adapted to prolonged colder periods when it would have been impossible for immature cicadas, known as nymphs, to emerge from the ground.

A Brazilian study published in 2004 suggested that most cicadas “didn't just settle on a random number, but instead found that intervals based on prime numbers — integers divisible by only one and themselves (3, 5, 7, 11, 13, 17, etc.) — offered the best breeding strategy for staying alive,” National Geographic reported April 19.

 

The true reason for the periodic cycle remains unknown, as well as how the cicada has somehow developed such an innate sense of time. During their long life underground, cicada nymphs survive on xylem fluids that they suck from tree roots. When their year to emerge finally arrives, the nymphs wait until the soil has reached a temperature of 18 degrees Celsius before venturing out. Following the East Coast spring climate, the Brood II cicada invasion will move from south to north. Some parts of North Carolina have already reported sightings.

CICADA PREDATORS INCLUDE HUMANS

For their first week above ground, cicada nymphs are easy targets for birds, reptiles, squirrels and even people. According to a May 6 article in Popular Mechanics, they have “been described as tasting like asparagus, popcorn, and pine cones,” and the magazine directs readers to a website featuring recipes for cicada-portobello quiche, cicada sauerbraten, cicada-cheese wontons, and German chocolate cicada cake, among other items.

At the same time, eating too many can reportedly result in painful stomach cramps. The American Humane Society has also warned pet owners that the plethora of insects can present a choking hazard and in large amounts can wreak havoc on animal digestive systems. Would-be human and pet consumers also need to beware of cicadas that have been treated with pesticides.

After a molting period of a few days, the adult cicada develops wings, discards its shell, and orients its entire life’s purpose toward reproducing the species. To attract a mate, the males group in trees and chirp what some consider the loudest sound to be produced by insects. They rapidly push air through an organ on their abdomen called a tymbal, and the sound is amplified due to the fact that their abdomens are somewhat hollow.

The noise level under a tree full of cicadas can reach 90 decibels, which is comparable to a small engine or a lawnmower. Scientists have found that along with attracting females, the loud noise repels and confuses birds. Males have apparently evolved to sing together and increase the total amount of noise in order to better protect themselves.

By mid-July, the cicada invasion will likely be over. Soon after the adults have mated and females have laid their eggs in tree limbs, they will die. In late summer, newborn nymphs will hatch and drop to the ground to burrow below the surface. The next generation of Brood II will return in 2030 to repeat this fascinating life cycle.