Billions of cicadas of the Great Eastern Brood, or Brood X, lurk beneath the ground of 15 U.S. states in parts of the Midwest and East Coast and are ready to reemerge this spring. This group of cicadas is known as periodical cicadas for their mysterious tendency to reemerge from the ground every 17 years. This year, 2021, marks 17 years since their last emergence in 2004. Once the weather reaches 64 degrees Fahrenheit, cicadas, in wingless nymph form, will burrow up to the surface. They are known for their large size, wings, and frightening appearance, but most notably for their ear-piercing buzz.

As stated by National Geographic, there are more than 3,000 species of cicadas that are classified roughly into two categories: annual cicadas and periodical cicadas. Annual cicadas emerge every year, but periodical cicadas, like those of the Great Eastern Brood, emerge almost every one to two decades. Periodical cicadas are split into 15 different brood cycles, each lasting 13 or 17 years.

The periodical cicada’s life cycle revolves around the brood cycles. As specified by National Geographic, the life cycle can be divided into three stages: egg, nymph, adult. Up to 400 eggs, split up in dozens of sites like twigs or tree branches, are laid by female cicadas. After 6-10 weeks, they hatch into nymphs and dig underground to suck plant root liquids. Here, they spend most of their life as a nymph, before molting their shells and surfacing as winged adults ready to mate and lay eggs.

Once on the surface, according to National Geographic, 1.5 million cicadas may crowd into a single acre. Rather than eating vegetation, cicadas stick to drinking sap from tree roots, twigs, and branches. Young trees can be damaged by a large cicada swarm, but old ones remain relatively unharmed as adult cicadas die off within 4-6 weeks. 

Though cicadas are not very damaging to the environment, they can be to the human ear! Because male cicadas’ natural instinct is to find a mate before they die, they release powerful chirps to attract females. National Geographic claims their calls can measure up to 100 decibels as they are amplified by their hollow abdomens.

Cicadas are sure to be an annoyance in the near future. On the bright side, they face many predators, die off quickly, and won’t be back for another 17 years anyway!