What are cicadas?
Cicadas are members of the superfamily Cicadoidea and are physically distinguished by their stout bodies, broad heads, clear-membraned wings, and large compound eyes.
There are more than 3,000 species of cicadas, which fall into roughly two categories: annual cicadas, which are spotted every year, and periodical cicadas, which spend most of their lives underground and only emerge once every decade or two.
Cicadas are famous for their penchant for disappearing entirely for many years, only to reappear in force at a regular interval. Despite their name, annual cicadas generally live for two to five years—though some species may live longer—and their brood life cycles overlap, meaning that every summer, some cicadas emerge. Even periodical cicadas occur most years in different geographic regions as they are split among 15 brood cycles, each lasting 13 or 17 years.
The cicadas’ amazing lifestyle has been a source of fascination since ancient times. Several cultures regarded these insects as powerful symbols of rebirth due to their unusual life cycles. In early Chinese folklore, cicadas were also considered high-status creatures that rulers should seek to emulate in their purity, and cicada motifs even became incorporated into imperial court wardrobes in the seventh century.
While annual cicadas can be found throughout the world, periodicals are unique to North America. Periodical broods are concentrated in the central and eastern regions of the United States, and some areas are home to multiple broods.
The cicada life cycle has three stages: eggs, nymphs, and adults. Female cicadas can lay up to 400 eggs divided among dozens of sites—generally in twigs and branches. After six to 10 weeks, young cicada nymphs hatch from their eggs and dig themselves into the ground to suck the liquids of plant roots. They spend their entire developmental period in these underground burrows before molting their shells and surfacing as adults to mate and lay eggs.
The developmental process varies in length, but periodical broods emerge in synchrony depending on the year and soil temperature. They wait for the right conditions for breeding, which are when the ground thaws to 65°F (18°C) in a brood’s designated year. It’s not clear why these cicadas have such distinct and oddly timed cycles, though some scientists theorize it has to do with avoiding predators.
Periodical cicadas do not create destructive plagues, as some locusts do, though as many as 1.5 million cicadas may crowd into a single acre. Unlike locusts, cicadas don’t eat vegetation but rather drink the sap from tree roots, twigs, and branches. Large swarms can overwhelm and damage young trees by feeding and laying eggs in them, but older trees usually escape without serious damage as cicadas don’t stick around for long. Adults die off within about four to six weeks after emerging.
Cicadas are also known for their buzzing and clicking noises, which can be amplified by multitudes of insects into an overpowering hum. Males produce this species-specific noise with vibrating membranes on their abdomens. The sounds vary widely, and some species are more musical than others. Though cicada noises may sound alike to humans, the insects use different calls to express alarm or attract mates.