Periodical cicadas

Lore & Background

Periodical cicadas belong to the genus Magicicada, within the tribe Cicadini (or sometimes Tettigadini, depending on classification), not Lamotialnini, which is a tribe of leafhoppers, not cicadas. They are often misnamed 'locusts,' but are true bugs (order Hemiptera), not grasshoppers. The seven species are distinguished by slight differences in size, coloration, and mating calls. Adults have red compound eyes, a black dorsal thorax, and translucent wings with orange veins; their abdomens vary in color by species.

Nymphs live underground for 13 or 17 years, feeding on xylem fluids from the roots of broadleaf forest trees. They emerge synchronously in late April to early June, triggered by soil temperature reaching about 17.9 °C at 20 cm depth. After emerging, they molt into adults and spend about six days hardening their wings and exoskeletons. Males form large choruses to attract females, producing species-specific songs that can reach 100 dB.

After mating, females lay eggs in slits cut into young twigs; the eggs hatch within 6–10 weeks, and the new nymphs burrow underground to begin the next cycle. The adults die by mid-July. Their mass emergence—sometimes over 1.5 million per acre—is a predator-satiation strategy, overwhelming predators so that enough survive to reproduce.

Reader's Guide

Periodical cicadas are significant for their extreme life-cycle synchronization and long developmental periods, which are rare among insects. Their emergences are major ecological events, providing a pulse of nutrients to forest ecosystems and affecting predator populations. The 13- and 17-year cycles are thought to be an adaptation to avoid synchronization with predator life cycles. The phenomenon has been studied for insights into evolutionary biology, population dynamics, and climate effects. Their emergence also impacts human activities: oviposition can damage young trees and shrubs, requiring protective measures like netting. The term 'periodical cicada' distinguishes them from 'annual' cicadas, which emerge every summer but actually have longer, overlapping life cycles. The species are also notable for their loud choruses and the misnomer 'locusts.' Their legacy includes scientific curiosity and public fascination during emergence years.

Did You Know?

• They are sometimes called 'locusts,' but are true bugs (Hemiptera), not grasshoppers.
• Males form choruses that can reach 100 dB in volume.
• Their mass emergence can exceed 1.5 million individuals per acre.

The Synchronized Emergence

The defining trait of the seven Magicicada species found across eastern North America is their extraordinary developmental synchronization. In any given locality, virtually every individual in the population reaches maturity and breaks the soil surface in the same calendar year, producing what observers describe as an emergence of tremendous numbers. These events occur in cycles of either thirteen or seventeen years, with the timing of the actual break-through shifting from late April in the far south to early June at higher latitudes. This collective timing is especially striking given the length of the cycle. It also distinguishes periodical cicadas from their nonperiodical relatives, where some adults appear each summer while the rest of the cohort continues maturing below ground. A common misconception is that so-called annual cicadas complete a one-year cycle, but documented lifespans for those species range from two to ten years. Periodicity is not unique to North America: a four-year cycle has been recorded in Chremistica ribhoi in northeast India, and an eight-year pattern in Raiateana knowlesi from Fiji.

The Underground Years

Roughly ninety-nine and a half percent of a periodical cicada's existence is spent as a nymph buried in the soil, typically no more than two feet below the surface. During this extended juvenile phase, the insect taps into the xylem of broadleaf tree roots, drawing water, minerals, and carbohydrates to fuel its growth. Nymphs pass through five distinct instar stages, and the difference between the thirteen-year and seventeen-year cycles is attributed to the additional time the second instar requires to mature. As they grow, the nymphs progressively burrow deeper, seeking out thicker roots to feed on. One of the most fascinating aspects of their subterranean life is how they apparently count the years. Evidence suggests they detect chemical shifts in the xylem that accompany a tree's seasonal leaf drop and regrowth. In a controlled experiment, researchers induced a grove of trees to shed and regrow leaves twice within a single calendar year; cicadas feeding on those trees emerged after sixteen years rather than the expected seventeen, confirming that the nymphs are tracking the tree's phenological cycles rather than relying on a fixed internal timer.

The Brief Adult Stage

After nearly two decades underground, the adult periodical cicada has only four to six weeks of surface life. Males gather in dense chorus centers and produce species-specific songs to lure receptive females; the decim species is said to sound like someone shouting weeeee-whoa or Pharaoh, while cassini and decula types interleave buzzing with ticking. Once mated, females use their ovipositors to slit pencil-sized twigs of woody vegetation and deposit eggs. This egg-laying can cause peripheral twig die-off, or flagging, in young trees, though mature specimens rarely sustain lasting harm. Gardeners are advised to postpone planting new shrubs during an emergence year or to wrap existing young plants in mesh netting with holes no larger than three-eighths of an inch. Within roughly two months of the first nymphs breaking the surface, all adults have died and the cycle is complete. Later that same summer, the eggs hatch, and the tiny new nymphs burrow into the earth to begin the next thirteen- or seventeen-year underground wait.

Taxonomy, Appearance, and Common Misconceptions

Despite the popular nickname locust, periodical cicadas are true bugs, belonging to the order Hemiptera and the suborder Auchenorrhyncha. Locusts, by contrast, are grasshoppers in the order Orthoptera. The genus Magicicada sits within the tribe Lamotialnini, a group whose members are distributed across Australia, Africa, Asia, and the Americas. Adult cicadas measure between 2.4 and 3.3 centimeters, roughly three-quarters the size of the annual cicadas sharing their habitat, with females slightly larger than males. Their bodies feature two red compound eyes, three small ocelli, a black dorsal thorax, and translucent wings threaded with orange veins; the ventral abdomen may be solid black, solid orange, or banded depending on the species. Contrary to popular fear, these insects are neither venomous nor poisonous and there is no evidence they can transmit disease. Their piercing mouthparts, designed for extracting plant sap, can accidentally poke human skin when the cicada is handled, causing a brief sting but no lasting harm.