Periodical Cicada (Magicicada septendecim): 17-Year Cicada Facts

What does a periodical cicada look like?

Adult periodical cicadas are easy to recognize. The body and upper thorax are black, the large compound eyes are red or red-orange, and the clear wings have bright orange veins. Between the big eyes sit three tiny simple eyes called ocelli. The legs are reddish-orange.

Magicicada septendecim has broad orange stripes across the underside of the abdomen and an orange patch on the side of the thorax between the eye and the base of the front wing. These marks separate it from the two smaller 17-year species, Magicicada cassini and Magicicada septendecula. Its closest relatives are two 13-year species, Magicicada tredecim and Magicicada neotredecim, which look almost identical and share a similar song. Scientists call these three the “decim” periodical cicadas.

A freshly molted adult is soft and creamy white, which leads to occasional reports of “albino” cicadas. The body darkens within hours, and the outer skeleton takes several more days to harden fully.

How big are periodical cicadas?

Magicicada septendecim is the largest of the seven periodical cicada species. Its body is about 27–30 mm (1.1–1.2 in) long, and with wings spread it measures up to about 7.5 cm (3 in) across. Females are slightly larger than males, and an adult female weighs about 1 g (0.04 oz).

Periodical cicadas are generally about three-quarters the size of the annual cicadas that sing in the same woods in late summer.

Where do periodical cicadas live?

All seven periodical cicada species live only in eastern North America. The 17-year species mostly occupy the northern part of this region, while the 13-year species live farther south and in the Mississippi Valley, with a little overlap.

Magicicada septendecim is the most widespread and most northern of the 17-year species. It ranges from southern New England and New York west through the Ohio Valley to the edge of the Great Plains, and south along the Appalachians. Within this area, broods are patchy, so one town may have millions of cicadas while another a few miles away has none.

The species depends on deciduous trees. Nymphs feed on the roots of oaks, maples, hickories and many other broadleaf trees, and adults need trunks and branches for molting, singing and egg laying. Forests, forest edges, old orchards, parks and leafy suburbs with mature trees are the best places to find them.

Life cycle: 17 years underground

The life cycle begins on a twig. After mating, a female uses her saw-like ovipositor to cut slits in pencil-thin twigs and lays about 20 eggs in each slit, several hundred in all. The eggs hatch after about six to ten weeks, and the tiny nymphs, only a couple of millimeters long, drop to the ground and burrow into the soil.

Underground, each nymph taps a tree root and sucks the watery sap that carries water and minerals up from the roots. This fluid is so poor in nutrients that growth is very slow. A nymph molts through five stages, called instars, mostly within about 60 cm (2 ft) of the surface, and moves to larger roots as it grows.

In spring of the 17th year, mature nymphs dig exit tunnels and wait just below the surface. When the soil about 20 cm (8 in) down warms to about 17.9 °C (64 °F), usually between late April and early June depending on latitude, they emerge in the evening in huge numbers, sometimes more than 1.5 million per acre. Each nymph climbs a trunk, post or plant stem, splits its skin along the back and pulls out as a winged adult, leaving its empty shell behind.

Adults live only about four to six weeks. By mid-July the whole brood is dead, and periodical cicadas spend roughly 99.5% of their lives underground.

Broods and mass emergences

Periodical cicadas that emerge in the same year in the same region form a brood. In 1907 the entomologist Charles Lester Marlatt numbered them with Roman numerals: I to XVII for 17-year broods and XVIII to XXX for 13-year broods. Many of these numbers never matched a real population. Today 15 broods are known to survive, 12 with a 17-year cycle and 3 with a 13-year cycle, while Broods XI and XXI have gone extinct.

Brood VII in upstate New York, known as the Onondaga Brood, is made up of Magicicada septendecim alone. In 2024 Brood XIII and Brood XIX emerged in the same year for the first time since 1803, although they barely overlapped in central Illinois. Because 13 × 17 = 221, the pairing will not repeat until 2245.

Why do periodical cicadas emerge together?

The main explanation is predator satiation. Birds, squirrels and other predators gorge on cicadas during an emergence, but there are simply too many for them to eat, so most survive long enough to breed. A cicada that came out in the wrong year would be eaten almost at once.

The prime-number lengths of 13 and 17 years may help too, because they rarely line up with the shorter population cycles of predators, and they may reduce crossbreeding between broods with different cycles. Nymphs seem to count years by sensing the yearly changes in the sap of their host tree. The evidence is explained in Why do cicadas come out every 17 years?

Song and courtship

Only males sing. Each has a pair of drum-like plates called tymbals on the sides of the abdomen, which buckle rapidly to produce clicks that merge into a continuous sound, amplified by the largely hollow abdomen. The calling song of Magicicada septendecim is a long, falling buzz often written as “Pharaoh” or “weeeee-whoa”.

Males gather in chorus trees, where the combined sound can reach about 100 decibels close by. They alternate bouts of singing with short flights from tree to tree, and a receptive female answers a male’s song with a well-timed flick of her wings. Males also make a quieter courtship song and a harsh alarm squawk when grabbed. The mechanics are explained in Why are cicadas so loud?, and cicadas also feature in the list of the loudest animals.

Diet and effects on trees

Periodical cicadas are herbivores that feed only on plant sap. They have no chewing jaws, just a sharp, straw-like beak that pierces roots or twigs. Adults do feed, contrary to a common belief, but only lightly.

Their biggest impact on plants comes from egg laying. The slits in twigs can cause the tips of branches to wilt and turn brown, a condition called flagging. Mature trees usually recover, but young trees can be badly damaged. Tree growth also dips slightly in the year before an emergence, when the large nymphs feed heavily on roots. After the brood dies, billions of bodies decay on the forest floor and release a pulse of nutrients into the soil. Cicadas cannot sting and seldom bite, as explained in Do cicadas bite?

Predators, parasites and partners

Almost everything in an eastern forest eats periodical cicadas during an emergence, from birds, squirrels, raccoons and foxes to snakes, turtles, fish, spiders and mantises. Moles and other burrowing animals eat nymphs underground. Some populations, such as wild turkeys, benefit from the feast, while moles may decline after the brood leaves the soil.

A fungus, Massospora cicadina, infects only periodical cicadas. It replaces the rear of the abdomen with a plug of spores while the infected cicada keeps flying and trying to mate, spreading the fungus to others.

Inside their bodies, periodical cicadas carry bacteria that supply nutrients missing from sap. One partner, Hodgkinia, has split into several separate lineages inside each cicada, all of which the insect needs to survive.

Conservation status and relationship with people

Magicicada septendecim was listed as Lower Risk/near threatened on the IUCN Red List in 1996, an assessment that has not been updated and corresponds to today’s Near Threatened category. Overall the species is still abundant, but clearing of forests has wiped out local populations, and two whole broods have disappeared since the late 1800s.

People in eastern North America have recorded periodical cicadas for centuries. The Finnish naturalist Pehr Kalm described the 1749 emergence in Pennsylvania, and Carl Linnaeus named the species Cicada septendecim in 1758 from Kalm’s account and specimen. Thomas Jefferson and Benjamin Banneker both noted the 17-year rhythm. For the Onondaga Nation, a cicada emergence in 1780, after a time of war and famine, is remembered as a gift that helped people survive.

Early European settlers called the insects locusts, a name that still lingers, but true locusts such as the desert locust are grasshoppers that chew crops, while cicadas only sip sap.