Periodical Cicada

Overview

The Periodical Cicada (Magicicada septendecim), known specifically as the 17-year locust or Pharaoh cicada, is an extraordinary, long-lived insect belonging to the true bug family Cicadidae endemic to the eastern United States. Renowned for spending seventeen continuous years underground as subterranean nymphs feeding on tree root sap, the species is instantly recognized by its striking black body, brilliant ruby-red compound eyes, reddish-orange legs, and clear, membranous wings with bright orange veins. Its synchronous, clockwork mass emergence every 17 years is one of the most astonishing biological phenomena on planet Earth.

In eastern deciduous forest ecosystems, the emergence of a periodical cicada brood represents an astronomical, once-in-a-generation ecological pulse of energy and nutrients. Billions of cicadas emerge simultaneously at densities exceeding 1.5 million per acre, executing an evolutionary survival strategy known as ‘predator satiation’: by overwhelming every bird, mammal, and fish predator with far more food than they could ever consume, the vast majority survive to mate. As their spent bodies die and decay, they deposit hundreds of tons of nitrogen and phosphorus into forest soils, triggering massive surges in microbial growth and tree ring widths.

Biology and Physical Characteristics

Magicicada septendecim is an evolutionary triumph of prime-number life-history timing and acoustic bioengineering. Mathematicians and evolutionary biologists note that its 17-year life cycle (and its sister 13-year species) uses prime numbers to prevent specialized predators from evolving matching cyclical life cycles. The male produces a deafening courtship song reaching 90 to 100 decibels—equivalent to a lawnmower—by rapidly buckling ribbed, drum-like membranes called tymbals located on the sides of its first abdominal segment, amplified by an enormous hollow abdominal resonance chamber. Females possess a strong, sword-like ovipositor that slits living tree twigs to insert clusters of eggs.

Behavior and Ecology

In May of their 17th year, when soil temperatures at eight inches deep reach exactly 64°F (18°C), billions of nymphs dig their way out of the ground simultaneously at dusk, scaling tree trunks and shed their nymphal skins within hours. The following morning, winged adults ascend into the high canopy, where males assemble into massive ‘chorusing centers’ that fill the forest with a hollow, humming roar often compared to a fleet of low-flying flying saucers (‘Pharaoh-oh’ song). Mated females lay hundreds of eggs in tree branches; six to eight weeks later, tiny ant-sized nymphs hatch, drop to the forest floor, burrow underground, and begin their next 17-year subterranean slumber.

Conservation and Human Impact

Magicicada septendecim has not been evaluated by the IUCN Red List due to its immense cyclical abundance across active broods. However, individual broods face severe localized extinction threats from suburban clear-cutting and deforestation; if a forest is paved over during any point in the nymph’s 17-year underground development, an entire generation of that locality is permanently extinguished. Brood XI in Connecticut went extinct in 1954, highlighting the need to protect mature urban tree canopies.

Interesting Factoid

Periodical cicadas spend 17 years living in subterranean darkness, counting the annual sap cycles of tree roots to keep time, only to emerge into the sunlight for a brief four-week summer frenzy of singing, mating, and dying.