Jan 22, 2024 - Science

2 cicada broods to co-emerge for first time in over 200 years

A female cicada clicks its wings while deciding on a mate in Burtonsville, Maryland, in 2021.

A female cicada clicks its wings while deciding on a mate in Burtonsville, Maryland, in 2021. Photo: Chip Somodevilla/Getty Images

Two specific broods of droning cicadas are expected to emerge from the ground simultaneously later this year, marking the first time in over 200 years that they've done so.

The intrigue: The last time Broods XIX and XIII co-emerged, Thomas Jefferson was president, and the Louisiana Purchase was being finalized.

What are cicadas?

Cicadas are a group of sound-producing bugs that spend much of their lives burrowed underground feeding on juices from plant roots before emerging aboveground to mate, either annually or in 13- and 17-year intervals, depending on the species.

  • They are between 1 and 1.5 inches long with wingspans twice that. They have black bodies, red-brown eyes and membranous orange wings.
  • Of course, they are also known for the male's mating call: a high-pitched buzz that's a classic sound of summer.
  • Periodic cicadas emerge in large broods made up of multiple species of cicadas that come above ground on the same cycle.
  • They will typically start emerging when forest grounds warm. This year, they're expected to begin in late April and early May.

The cause of mass cicada emergences is still being researched, but it is currently believed to have evolved in response to predators.

  • Since they are eaten by pretty much everything — even some fungi — and have few ways to defend themselves, cicadas may have adapted to erupt from the ground in such large amounts that predators couldn't consume them all.
  • It's a passive defensive mechanism called predator satiation. Predators can eat to the point of disgust and exhaustion, and the surviving cicadas will still have a chance to mate and lay their eggs in tiny holes in tree or shrub branches.

How many cicadas will there be this year?

Trillions of cicadas will likely emerge across the U.S. this year, though population sizes are extremely difficult to predict.

  • It's generally estimated that there can be around a million cicadas per acre, but populations are greatly affected by the amount of deforestation, urbanization and wildfire that's taken place in preceding years, according to the University of Maryland.

Yes, but: Though the co-emergence will be historic, there likely won't be an abnormal amount of cicadas this year, according to the University of Connecticut.

  • They'll emerge at the same time, but their ranges don't significantly overlap, meaning cicada density should appear normal.
  • If there is geographic overlap, it will be hard to tell. Though there are different species in broods, their unique appearance and sound varies only slightly.
  • And while trillions may emerge, their population will be spread across a massive portion of the country.

What states will see cicadas this year?

Parts of at least 16 states are expected to see the insects this year:

  • Alabama, Arkansas, Georgia, Iowa, Illinois, Indiana, Kentucky, Louisiana, Maryland, Missouri, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee and Virginia.

What's special about the upcoming broods?

The upcoming 13-year Brood XIX, called the Great Southern Brood, is considered to have the largest range of all periodical broods.

  • It's been nine years since a 13-year brood emerged in the same year as a 17-year brood.
  • Broods XIX and XIII haven't specifically co-emerged since 1803.

Should I kill cicadas?

Being harmless and beneficial to local environments, they are far from pests and shouldn't be deliberately killed.

  • They can't harm pets, gardens, crops or people. (They may worsen certain hearing conditions but permanent damage from their sound is unlikely.)
  • At most, they should be managed by protecting younger trees, as they can cause some damage while laying their eggs, according to the Environmental Protection Agency.
  • The damage can be prevented by covering vulnerable trees in mesh or netting.

How are cicadas affected by climate change?

Human-caused climate change is expected to alter the current life cycles of periodic cicadas species, per University of Connecticut.

  • They are cued to emerge by soil temperatures and the annual cycles of the plants they feed on.
  • But a warming climate is expected to force spring to arrive sooner and change plant cycles, which will likely cause cicadas to come aboveground earlier.
  • This could lead to more and more "stragglers," or cicadas that appear either before or after their brood is expected to emerge, causing a breakdown in the insects' miraculous periodicity.

Researchers are still studying how these alterations could affect cicadas species and ecosystems.

  • The bugs have existed for millions of years and have seen and survived drastic changes to the climate in the past, though those changes took place over a substantial amount of time.
  • It's unclear if they could adapt during a period of severe and rapid climate change.

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