Periodical cicada

Baby cicadas drink juice from tree roots.

Grown-up cicadas drink juice from twigs. They use a mouth like a straw.

Cicadas drink their food. Underground, the young cicadas, called nymphs, push their needle-like mouthparts into roots and suck up the watery juice inside. They start on grass roots and later move to tree roots.

Many people think adult cicadas never eat, but they do. Adults suck juice from the twigs of many kinds of trees and shrubs, but usually not from grass. Without living woody plants to feed on, an adult cicada dies.

Cicadas have piercing-and-sucking mouthparts. Nymphs tap roots for fluid throughout their 13 or 17 years; Penn State Extension notes that newly hatched nymphs feed first on grass roots and then on tree roots. Feeding by hundreds or thousands of nymphs on one tree's roots for 17 years probably affects its productivity, though this has never been fully documented.

Contrary to popular belief, adults also feed, sucking fluids from a wide variety of deciduous trees and shrubs but usually not grasses, and they die if they have no living woody vegetation. Their mouthparts are used only for feeding on twigs, which is why the University of Connecticut jokes that a cicada can hurt you only if it mistakes you for a branch.

Boy cicadas sing very, very loudly.

They sing together in big groups. Girl cicadas do not sing. They listen and fly to the singers.

Only male cicadas sing. They make sound with their tymbals, and they gather in big groups called choruses. Together, the males make an ear-splitting, high-pitched whine.

Female cicadas make no song, but they are drawn to the singing males. Each kind of cicada has its own song, so scientists often tell cicadas apart by listening. You can hear a real recording of a periodical cicada's song at the start of this page.

After their teneral period, males produce species-specific calling songs and gather in choruses that are sexually attractive to females. Males alternate bouts of singing with short flights until they find receptive females. Penn State Extension describes the males' sound as an ear-splitting, high-pitched whine; females produce no song.

Because cicada songs are nearly always species-specific, sound is the best way to identify cicada species. If handled, males also make a loud defensive buzz, which may startle but is otherwise harmless.

So many cicadas come out at once.

Birds and other animals eat lots of them, but there are far too many to eat them all. That keeps most cicadas safe.

Periodical cicadas can come out in astonishing numbers: sometimes hundreds of thousands, or even more than a million, on a single acre of land. Birds, spiders, snakes and even dogs feast on them.

But the predators get full long before the cicadas run out. Scientists call this predator satiation. And because cicadas appear only once every 17 years, no predator can depend on them, so predator numbers cannot build up to match. Periodical cicadas are also slower and easier to catch than other cicadas.

Densities of tens to hundreds of thousands per acre are common, and a 1956 census of Brood XIII in Raccoon Grove, Illinois, recorded figures above a million per acre. Through predator satiation, predators eat their fill without significantly reducing the population, and because the cicadas are available only once every 13 or 17 years, predator populations cannot build up in response.

Why periodicity evolved is still debated. Hypotheses invoke glacial cycles or predation pressure, but the University of Connecticut team argues that neither is sufficient, since most temperate insects faced both yet very few are periodical. Of perhaps more than 5,000 cicada species worldwide, fewer than 10 are periodical, and seven of those are Magicicada.

Cicadas do not hurt people.

They can hurt very young trees by laying eggs in their twigs. Gardeners put nets on small trees to keep them safe.

On the IUCN Red List, this periodical cicada is listed as near threatened, in an old assessment from 1996 that the Red List says needs updating. Periodical cicadas depend on living trees and shrubs for their whole lives, for food as nymphs and adults and for laying eggs.

Cicadas do not sting or bite, and they are not poisonous. They can damage very young trees, because the egg slits weaken thin twigs. Gardeners protect small trees by covering them with fine netting while the cicadas are laying eggs.

The IUCN Red List's only assessment of Magicicada septendecim, made in 1996 under the older 2.3 criteria and flagged as needing an update, places it in the category Lower Risk/near threatened. Broods depend on living woody plants throughout their lives, as nymphs, as adults and for egg-laying.

For people, cicadas are harmless, but egg-laying slits can kill branch tips, and trees four years old or younger, whose branches are mostly the preferred size, can be severely damaged. Penn State Extension recommends covering small trees with netting of no more than about quarter-inch mesh during egg-laying and delaying winter pruning of young trees. The University of Connecticut team notes that the best way to predict an emergence is to check local records from the previous one, 17 years earlier.