17-Year Cicadas Swarm the East Coast

cicada

After 17 years underground, Brood II cicadas are making a reappearance this summer along the East Coast. (Photo credit: Shutterstock)

Residents along the East Coast, from northern North Carolina to upstate New York and beyond, are experiencing the emergence of Brood II cicadas. These funky-looking insects–with their bulging red eyes, large black bodies, three sets of red legs, and orange-veined wings–were last seen 17 years ago. Well, technically speaking, it was the parents of the now-emerging cicadas that were last seen in 1996. Do you remember what you were doing 17 years ago? If you are in high school now, there’s a good chance you weren’t even born yet!

Though often confused with locusts, cicadas actually are more closely-related to aphids and crickets, and belong to the order Homoptera, which includes insects that have piercing and sucking mouthparts. There are three main types of cicadas: those that emerge every 13 years, those that emerge every 17 years, and those that emerge annually in late summer. Broods that emerge every 13 or 17 years (also called periodical cicadas) are in the genus Magicicada. Brood II cicadas, which are the ones emerging this year along the East Coast, belong to the species Magicicadaseptendecim–septendecim means seventeen in Latin.

In all, there are 12 different broods of 17-year cicadas and three different broods of 13-year cicadas. Periodical cicadas are found mainly in the eastern half of the United States. Last year, Brood I (17-year) cicadas emerged in Virginia, West Virginia, and Tennessee. Next year, Brood III (17-year) cicadas are expected to emerge in Iowa, Illinois, and Missouri; and Brood XXII (13-year) cicadas are expected to emerge in Louisiana and Mississippi.

A cicada spends the majority of its lifetime underground. For a Brood II cicada, its life cycle began 17 years ago when it emerged as a nymph from an egg laid on a tree branch. After hatching, the nymph dropped to the ground and burrowed its way into the dirt. There it remained for the majority of its lifetime. While underground, the cicada fed by sucking xylem from tree and shrub roots.

Scientists aren’t quite sure how the cicadas know when to emerge from their underground homes. They think it might have something to do with plant hormonal signals that alert the insects to the passage of seasons. Scientists do know that the emergence of cicadas requires soil temperatures to reach 64 degrees Celsius eight inches below the surface; hence the insects typically emerge in late spring or early summer.

Once the cicadas emerge from the ground, they get right down to business. They climb to the top of the nearest tall object and molt into their adult forms. The cicadas then have less than four weeks to find a mate and lay eggs. Following maturation, the male cicadas sing to attract females. When a large group of males call out for mates at the same time, their song can be nearly deafening. (In fact, the songs of some cicada swarms can approach 120 decibels at close range.) Females do not sing. Instead, they judge the males on the quality of their song and then choose a mate. After mating, the female uses its ovipositor–a spike-like apparatus on its abdomen–to cut small slits in a tree branch. These slits will serve as the repository for her eggs, the source of the next population of cicadas that will sing and mate 17 years later. Following mating and laying eggs, the adult cicadas tend to die en masse, leaving behind millions upon millions of decomposing bodies.

When the Brood II cicadas fully emerge, their numbers will be quite impressive. Their population densities can range from tens of thousands of cicadas per acre to more than 1.5 million individuals per acre. Researchers think the insects emerge in such large numbers as part of a survival strategy called predator satiation. The idea behind this strategy is that the huge number of cicadas overwhelms their predators, as they can only eat so many cicadas at one time. Given a cicadas lack of defenses, scientists estimate that up to 40 percent of Brood II may be eaten prior to having a chance to mate, but with such large population numbers, that still leaves a billion (yes, 1,000,000,000) cicadas with a chance to mate before dying.

Surprisingly, unlike swarms of grasshoppers or locusts, cicadas contribute little to no damage to an ecosystem. As adults, they do not eat, instead focusing all their energies on mating. While the females do inflict some damage on tree branches when they lay their eggs, this damage is typically not long term. Cicadas do not bite or sting, and are not poisonous. However, the Humane Society does warn against allowing pets to eat too many of the insects, as their chitinous bodies can cause digestive problems. For humans, cicadas tend to be more annoying than anything else–as poor flyers, there is a good chance you will be crash-landed upon by several if you walk through a particularly dense swarm. Their song can also be distractingly loud–the cacophonous noise levels can even repel birds, as it is painful to birds ears and can interrupt their communications while hunting.

The emergence of cicadas actually appears to have some positive impacts on ecosystems. For example, studies have shown that populations of red-wing blackbirds, eastern bluebirds, foxes, and raccoons all have stronger and healthier broods in years that coincide with the emergence of cicadas. After falling to the ground, the cicadas molted exoskeletons provide an excellent source of nitrogen for trees. The decomposition of adult cicada bodies also helps to produce rich and fertile soil.

Given their unusual life cycles, 13- and 17-year cicadas prove a difficult subject to study for scientists. A scientist may only get three or four chances to study the emerging insects during his or her career. Dr. Chris Maier, an entomologist with the Connecticut Agricultural Experiment Station in New Haven, Connecticut, has had the chance to study their emergence three times thus far–in 1979, 1996, and this year. The next time Brood II reemerges, in 2030, Maier will be 81 years old! Current questions that scientists are studying include interactions among different cicada broods, developmental anomalies, and hybridization.

More to Explore
Cicada Tracker
Cicada (viaNational Geographic)
17 Years to Hatch an Invasion
Periodical Cicada (via Chicago Botanic Garden)
2013 MagicicadaBrood II Reports
Mid-Atlantic Cicada Database Project
Cicadas Coming to U.S. East Coast This Spring
Periodical Cicada Broods

Comments

  1. Emma Brown says:

    I think there gross and too loud and im glad they only come out every 13-17 years

  2. Dylan Calvo says:

    I remember how annoying, ugly, loud, and big these monsters were, but most of all, I remember how good of target practice they were for my paintball gun. I wish they would come more often. Too bad they will only come around at most 4 times in my life.

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