Five myths about periodic cicada emergence

John Lill is a professor and the chair of biological sciences at George Washington University, where he studies the ecology and evolution of plant-insect interactions. Zoe Getman-Pickering is a postdoctoral scientist at George Washington University, where she researches the ways that periodical cicadas shift forest food webs.

After spending 17 years underground, billions of cicadas soon will emerge to sing, mate, lay eggs and die. Americans on the East Coast will have the rare opportunity to witness this dramatic natural spectacle. But as these magnificent insects begin to surface, so does misinformation about them.

Myth 1: Cicadas are invading

Soon, young cicadas, known as nymphs, will crawl up trees, bushes, fences and houses, looking for a place to molt. The adults will fill the air in neighborhoods far and wide. Their singing will be deafening. Because the cicadas will show up rather suddenly en masse, it is easy to see how people might view this as an “invasion.” An ABC News headline, for instance, calls the coming emergence a “cicada invasion.” The AARP website warns, “Billions of Bugs Set to Invade Eastern U.S.,”as if the insects are breaching our human communities from elsewhere.

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In fact, North American periodical cicadas are native to most of the Eastern United States and have been here for millions of years, according to evolutionary biologists. From the cicadas’ perspective, humans are the invasive species that has been systematically destroying the forests they rely upon.

Myth 2: Cicadas are dormant between emergences

Brood X has not been seen for nearly two decades (beyond a few individuals that emerged early in 2017). Because humans cannot see what subterranean cicada nymphs are up to, it’s easy to assume that they are doing nothing. Many writers, from those at The Washington Post to the New York Post, have done just that, in articles that describe how the insects supposedly burrow into the soil and lie “dormant” or even “hibernate” for 17 years.

In fact, cicada nymphs are far from dormant. They move, albeit infrequently, among feeding locations. The newly hatched nymphs, usually between 1 and 1 1/2 inches long, start out eating the fine roots of grasses and nonwoody plants before delving deeper to dine on tree roots; each move involves excavating soil to locate a new site. Deeper underground, nymphs build protective feeding chambers, where they eat, grow and molt over many years. The cicada nymphs also build little walls of hardened dirt around these feeding chambers, to shield themselves from predation. As their emergence date draws closer, the cicadas dig back up to the surface. Within these vertical chambers, they spend several weeks monitoring local conditions, such as temperature and day length, so they can precisely time their emergence to coincide with their many compatriots. Although they probably reduce their activity during the coldest days of winter, there is no evidence that the cicadas hibernate.

Myth 3: Cicadas are a type of locust

When settlers and the enslaved people they brought with them arrived in North America, they believed that locust plagues were a form of divine punishment, based on stories in the Koran, the Torah and the Bible. Migratory locusts (Locusta migratoria) were - and are - infamous for forming huge swarms that blotted out the sun; they would cover fields in many parts of the world, devastating crops and causing famines. Seeing millions of cicadas flying around their communities, the settlers jumped to the conclusion that these “singular flies” were locusts, as one Philadelphia clergyman documented in a 1715 diary entry. More than 250 years later, this “17-year locusts” misnomer lives on, in sources from the Berkshire Eagle to the outreach websites of Purdue and Rutgers University’s agricultural extension programs.

Cicadas are not locusts, a common name given to several species of grasshoppers that tend to form highly mobile feeding aggregations. Locusts are insects in the order Orthoptera, which includes katydids and crickets. Cicadas are part of the order Hemiptera, or true bugs, and are more closely related to aphids and leafhoppers. Unlike locusts, periodical cicadas do not feed on crops, and they do not migrate. They have strawlike sucking mouthparts for feeding on sap from underground roots, whereas locusts have chewing mouthparts.

Myth 4: Cicadas harm the environment

The fear that cicadas will hurt nonwoody plants probably stems from the conflation of cicadas and locusts. This misconception even showed up on the TV show “Silicon Valley,” which claimed that periodical cicadas in Brazil and Myanmar would devastate sesame seed crops (though periodical cicadas are not known to occur in those countries). Companies have eagerly capitalized on the confusion by selling pesticides and netting to protect plants.

Periodical cicadas, one of the East Coast’s thousands of native herbivore insect species that use woody plants as sustenance, are not known to kill the plants that serve as their hosts. Nor do they appear to transmit any plant diseases. As adults, the females can cause minor damage to the twigs of trees and shrubs where they lay their eggs. Except small saplings, which can be protected with netting during the brief period of cicada egg-laying, most trees suffer little lasting harm. Some researchers have recorded increased tree growth the year after cicada emergences, possibly because of the soil aeration and nutrient additions that are byproducts of the event. Far from harming the environment, the emergence and death of cicadas often have strong positive effects on other organisms, including the many animals that eat them, and the plants, fungi and microbes that absorb the nutrients from the insects’ decaying bodies.

Homeowners cannot suppress cicada populations by applying pesticides. That tact probably would kill countless other insects while introducing potentially harmful chemicals into the environment. Buying netting to protect nonwoody vegetables and flowers will line the pockets of the suppliers but it is unnecessary.

Myth 5: Cicadas increase the risk of encountering snakes

The Internet recently has been captivated by the idea that the cicada emergence will increase the risk of attacks from venomous snakes. “Cicadas Swarm And Copperheads: Yes, It’s A Thing In Maryland,” claimed a recent Patch article. “Don’t be surprised if you see copious amounts of copperheads coming out to enjoy an easy cicada snack,”warned a New Jersey radio station. The theory goes that venomous snakes will emerge from their nooks and crannies to feed on the insects - ending up in places where unwary humans might step on them.

While some snakes eat periodical cicadas, there is no evidence that this raises the danger of snakebites to humans. The original Tulsa World article on this phenomenon reported on a man in Arkansas who snapped a picture of a copperhead eating an annual cicada (a different species entirely). To our knowledge, there are no documented cases of copperheads consuming periodical cicadas, and no published research supports the suggestion that this would pose a risk to humans. Periodical cicadas have emerged every 13 or 17 years in copperhead territory without any reported increase in snakebites during those events.

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