Brood X Periodical Cicadas: Answers to Common Questions

Periodical cicadas are black with orange and red — never green. Green cicadas are annual cicadas. NPS/Nortrup.

What are they?

• Periodical cicadas are insects in the order Hemiptera (true bugs). They feed on plant fluids (xylem) above and below ground.
• Brood X ("X" is 10 in Roman numerals) is the largest brood of 17-year cicadas. It lives in three separate areas, centered on Pennsylvania and northern Virginia, Indiana, and eastern Tennessee, and emerges as adults only once every 17 years.
• There are 7 species of periodical cicadas — one only recently described — with 3 in the Washington, D.C., area. Annual cicadas (the green ones) come out every year.
• There are 12 broods of 17-year cicadas and 3 of 13-year cicadas (none near D.C.). Two broods have gone extinct, one near Connecticut and one in Florida. The broods have moved northward since the last ice age.
• They are native, not invasive.

When?

In 2021, emergence depended on the weather: it begins when the ground reaches 64 degrees, predicted for the first or second week of May, with the cicadas gone by the end of June. (Annual cicadas are out June–August.)

Why all at once, every 17 years?

Prey satiation: there are so many cicadas that predators — birds, raccoons, opossums, foxes, mice, shrews, frogs, toads, turtles, fish, and even a fungus called Massospora — eat their fill and plenty are left to breed.

Life cycle

1. Underground: nymphs pass through 5 stages (instars) over 17 years, drinking sap from tree rootlets.
2. Emergence: males come out first; adults live about a month and die after mating.
3. Eggs: each female lays about 500 eggs in young tree branches.
4. Hatching: about six weeks later, tiny nymphs drop to the ground and burrow in for another 17 years.

Stragglers: smaller numbers emerge after 13 or 21 years, because nymphs grow at different rates.

The song

• Only males sing, calling females; a willing female answers by clicking her wings.
• The sound comes from vibrating drum-like organs on each side of the body near the base of the wings.
• Each species has its own song, and together they make a blended chorus.
• Male cicadas are the loudest insects; entomologists think the noise may protect them by hurting predators' ears.

"if their lives are short they are merry, they begin to sing or make a noise from the first they come out of earth till they die." — Benjamin Banneker

Effects on the environment

• Young trees can be harmed, because females cut into young branches to lay eggs. Spring 2021 was a poor time to plant small trees: plant in fall, or protect spring plantings with netting.
• The emergence is a feast for wildlife; some birds lay larger clutches in cicada years.
• Dead adults fertilize the soil under the trees where their offspring will feed.

Are they safe?

• Yes. They don't bite or sting.
• They are not toxic to pets in small amounts.
• People with a shellfish allergy may also be allergic to eating cicadas.

Eyes: nearly all have orange-red eyes; rare mutants have blue or white. Cicadas have five eyes — two large red ones and three small dark ones between them.

What you can do

• Enjoy them while they're here.
• Don't use insecticides — they won't control cicadas and may hurt beneficial insects.
• Add dead cicadas to your compost.
• Help scientists track the brood with the Cicada Safari app.

Sources

Based on "Brood X Periodical Cicadas FAQ," National Park Service (National Capital Area parks); a work of the United States government in the public domain. The original names the sound organ the "tympanic membrane"; cicadas hear with their tympana but sing with a separate pair of ribbed membranes, the tymbals, so the organ is described here without the name. The brood map, credited to Cicadas.Info, is left out.