What Are Brood X Cicadas? (2024)

Brood X cicadas emerge every 17 years in 15 states throughout the Eastern and Midwestern United States. Of the 12 active periodical cicada broods, Brood X (pronounced "Brood 10") is one of thelargest and most concentrated, comprising all three known 17-year cicada species,Magicicada septendecim,Magicicada cassini, andMagicicada septendecula.

On select years, in late April to early May, billions of these large-winged arthropods emerge from the ground simultaneously, promptly blanketing the trees in discarded exoskeletons and filling the air with their vociferous, rhythmic mating calls. Despite their unsettling appearance — with veiny mega-wings and bulging red eyes — cicadas are harmless. They don't bite humans or harm the mature trees that temporarily house them. They may, however, hinder the growth of a juvenile tree (but for that, there's netting).

Learn more about the world's potentially densest, most widely distributed cicada brood and what to expect when it arrives.

Brood X Cicadas

The first mention of Brood X was in a 1715 journal entry by Philadelphia pastorRev. Andreas Sandel. Another mention of them decades later — in a letter by botanist John Bartram describing their1732emergence — verified their 17-year periodicity. While their distribution is believed to have once been wider, they now occur most heavily in Maryland, Indiana, Ohio, Tennessee, and parts of Pennsylvania, Delaware, New Jersey, Illinois, North Carolina, and Georgia.

"Brood X historically included a large swath of the mid-Atlantic, west to Ohio and Indiana, and south to Kentucky and Tennessee," says Dr. John Lill, chair of George Washington University's Department of Biological Sciences. "But intensive deforestation, followed by farming and/or grazing, likely reduced and fragmented Brood X into its current distribution (the exact causes of the current distribution remain a bit of a mystery)."

It's no mystery, however, why U.S. periodical broods tend not to travel outside their longtime territory. Dr. Zoe Getman-Pickering, a postdoctoral scientist at GWU, says they're "relatively helpless" because their only individual survival mechanism is singing (at 120 brain-rattling decibels, no less), so when they stray from the swarm, they're more likely to become meals for birds, rodents, snakes, and mammals. Thus, they rely on their strength in numbers — and Lill says there could be up to a trillion of them.

Besides, they feed on tree roots as nymphs, and the grassy plains of the Midwest simply can't support them, says Getman-Pickering.

What Are 17-Year Cicadas?

There are two types of cicadas: annual and periodical. There are seven species of periodical cicadas in North America — four that emerge every 13 years and three that emerge every 17 years. Experts believe the longer periodicity of 17-year species iscaused by colder temperatures, as 13-year broods are more common in the warmer Southern states.

Life Cycle

The lifespan of a cicada is concurrent with its periodicity — so, 17-year cicadas live 17 years, and so forth. They drop from cracks and holes in trees to the ground immediately upon hatching six to 10 weeks after their eggs are laid, then they burrow underground and find a patch of tree root to live on for the next 17 years. Cicadas are not exactly dormant during their juvenile phase (in which they're called nymphs). Rather, they spend nearly two decades just feeding on xylem and waiting for their next emergence, which they may be able to determineby monitoring the trees' blossoming cycles underground.

When the ground 8 inches below the surface reaches 64 degrees Fahrenheit — usually late April or early May — the cicada nymphs will tunnel to the surface and climb up a nearby tree to evade ground predators. They shed their exoskeletons (exuviae) during the last growth cycle, and once their wings inflate with fluid, they take flight — singing their piercing calls to attract mates all the while.

Brood X cicadas emerge every 17 years (1987, 2004, 2021) and live only up to six weeks above ground. Females lay about 500 eggs each before they retire, and then the cycle repeats.

What Are Brood X Cicadas? (3)

Are Cicadas Dangerous?

Cicadas are not dangerous to anyone or anything except, perhaps, juvenile trees. Cicadas continue to feed on trees once they emerge from the ground, and if you have trees whose main branches are less than a half inch in diameter, their feeding and egg-laying can cause damage. You can easily protect juvenile trees by covering them with mesh. It's best to not use insecticides as the chemicals can compromise future cicada generations.

Cicadas do not bite or sting. They're so harmless that animals — including cats, dogs, and even humans — eat them.

Report Cicada Sightings

What Are Brood X Cicadas? (4)

All three Brood X species are listed as Near Threatened on the IUCN Red List. "The populations are definitely declining," Getman-Pickering says, and the main culprits are climate change and deforestation.

Whereas large quantities of Brood X cicadas once emerged on Long Island, the New York City-adjacent refuge now sees very few. To monitor populations across the region, cicada expertDr. Gene KritskyofMount St. Joseph University developed a free citizen science app calledCicada Safariwhere people can upload photos of Brood X and future broods. The goal is to map cicada sightings for future research.

Additionally, Lill says people in cicada-prone regions can help conserve the prehistoric critters by planting trees, supporting conservation organizations (particularly local ones that promote reforestation efforts like Chesapeake Bay Program, Casey Trees, the National Forest Foundation, American Forests, and The Nature Conservancy), and voting for local development projects that protect forest lands.

What Are Brood X Cicadas? (2024)


What Are Brood X Cicadas? ›

Brood X is a type of periodical cicada. Periodical cicadas are the cicadas that have a long life cycle. So they're every 13, or every 17 years. Brood X happens to be a 17-year cicada, which means the last time it was out of the ground was 2004.

What do Brood X cicadas do? ›

Map of periodic cicada broods with Brood X shown in yellow. Every 17 years, Brood X cicada nymphs tunnel upwards en masse to emerge from the surface of the ground. The insects then shed their exoskeletons on trees and other surfaces, thus becoming adults.

What are the main activities the Brood X cicadas will be involved in while they are above ground how long will they last? ›

After they've found a tree or shrub to land on, the cicadas will mate and lay eggs at the end of branches. Newly hatched cicadas will then chew through the branch tips, causing them to fall off, carrying the young insects back down to the soil where they will spend the next 17 years.

What are cicadas good for? ›

Benefits of Cicadas

Cicadas are not dangerous and can provide some environmental benefits including: Cicadas are a valuable food source for birds and other predators. Cicadas can aerate lawns and improve water filtration into the ground. Cicadas add nutrients to the soil as they decompose.

Do cicadas really sleep for 17 years? ›

Cicadas do not hatch out of the ground (they hatched from eggs in tree branches 17 years ago), and they do not “hibernate” (they are underground actively feeding). When they moult to become adults, the correct term for that process is “ecdysis.”

What bug comes out every 17 years? ›

Crawling out from underground every 13 or 17 years, with a collective song as loud as jet engines, the periodical cicadas are nature's kings of the calendar. These black bugs with bulging eyes differ from their greener-tinged cousins that come out annually.

Why 17 years for cicadas? ›

As trees go through their seasonal cycles, shedding and growing leaves, the composition of their sap changes. And when cicada nymphs feed on that sap, they likely pick up clues about the passage of time. The 17th iteration of the trees' seasonal cycle gives the nymphs their final cue: it's time to emerge.

Can cicadas hurt you? ›

Cicadas are largely harmless to humans and animals. They don't bite and they don't sting. They lack the physical structures to hurt people that other insects have: they don't have stingers so they can't sting and their mouth parts are a more like a straw than teeth so they can't bite.

What is so bad about cicadas? ›

They don't sting or bite, and are not poisonous. In fact, the Environmental Protection Agency (EPA) says they can be a great food source for birds and are nutritious for the soil once they decompose. They may be damaging to young trees if female cicadas decide to lay their eggs in one.

Are cicadas harmful? ›

Cicadas are not dangerous. They do not sting or bite because they don't have the appropriate mouthparts. They're also not harmful to pets, crops or gardens. Cicadas won't eat leaves, flowers, fruits or vegetables, although they may eat some sap from trees and shrubs, the EPA says.

Are cicadas good or bad for the garden? ›

They're not as bad as they seem

They don't bite, they don't sting, they don't spread disease, and despite their swarming numbers, they don't do much landscape damage. The main plant-injury threat comes from egg-laying. Female cicadas cut small slits in young tree branches, then lay little white eggs in them.

Are cicadas good or bad for trees? ›

Cicadas damage fruit trees in two ways. The most obvious damage is done during the egg-laying process. The slits made by the female in small branches severely weaken them; often the weakened branches snap off in the wind. Under a heavy attack a majority of the branch tips may be killed.

Do cicadas bite or sting? ›

Periodical cicadas don't bite or sting, and they're harmless to humans, animals and most plants, Lawrance added. But they are noisy.

What do cicadas turn into? ›

Periodical cicadas are insects that spend most of their lives underground as nymphs, feeding off the sap of tree roots. They emerge to transform into adults and mate. Some periodical cicadas emerge every 13 years and others emerge every 17 years. The males "sing" by vibrating a membrane on the sides of their bodies.

What is the lifespan of a cicada? ›

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.

What happens when cicadas mate? ›

Next, male cicadas fill the air with shrill buzzing sounds created by rapidly vibrating drum-like plates on their abdomens. The females make clicking sounds with their wings if they like the song. They mate, lay their eggs, and then both male and female cicadas die after just about five weeks aboveground.

What do cicadas do after mating? ›

After mating, the female makes slits in tree branches and lays eggs there. The eggs hatch six to seven weeks later, the nymphs fall to the ground and go into the soil, and the cycle begins again. The adult periodical cicadas only live three to four weeks.

What do cicada nymphs do? ›

The cicada nymphs hatch from their eggs in trees. After a few days, they fall to the earth and burrow underground, where they spend their time tunneling through dirt and eating the sap from tree roots. They live that way for 17 years in their nymph form.

What do cicada killers do with cicadas? ›

The cicada killer wasp gets its name from, as you would guess, killing cicadas. The female cicada killer wasp has a stinger that she uses to inject venom into cicadas, not killing the cicadas but instead paralyzing them. She then flies the cicada to her nesting area, dragging it underground.

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