Get Ready: A Huge Cicada Swarm is Coming to the US

Following North America’s recent solar eclipse, another significant natural phenomenon is approaching. Between late April and June 2024, the largest group of 13-year cicadas, known as Brood XIX, will emerge alongside a midwestern group of 17-year cicadas, Brood XIII.

This phenomenon will impact 17 states, stretching from Maryland to Iowa and extending southward into Arkansas, Alabama, northern Georgia, the Carolinas, Virginia, and back to Maryland. The simultaneous emergence of these two distinct broods with different life cycles occurs once every 221 years. The last occurrence was in 1803 during Thomas Jefferson’s presidency.

For approximately four weeks, the sounds of cicadas’ unique calls will fill scattered wooded and suburban areas. After mating, each female cicada will deposit hundreds of eggs in pencil-thin tree branches before the adult cicadas perish. Once hatched, the new cicada nymphs will drop from the trees, burrow underground, and initiate the cycle anew.

While there are an estimated 3,000 to 5,000 cicada species worldwide, the 13- and 17-year periodical cicadas of the eastern US stand out for their lengthy underground juvenile phase coupled with synchronized, mass adult emergences. Two other known periodical cicadas exist globally, one in northeast India and another in Fiji, but their life cycles span four and eight years, respectively.

The unique life cycle of periodical cicadas prompts numerous questions from entomologists and the general public alike. What do these cicadas do underground for 13 or 17 years? Why are their life cycles so extended? What causes their synchronization? Will the two broods emerging this spring interact? How can citizen scientists contribute to documenting this emergence? And finally, is climate change impacting this remarkable insect phenomenon?

We research periodical cicadas to explore questions related to biodiversity, biogeography, behavior, and ecology, delving into the evolution, natural history, and geographic distribution of life. The scientific name for these 13- and 17-year cicadas, Magicicada, is fittingly derived from “magic cicada,” reflecting their intriguing nature.

Visitors from the Past

As a species, periodical cicadas predate the forests they occupy. Molecular studies indicate that around 4 million years ago, the ancestor of today’s Magicicada species diverged into two lineages. Approximately 1.5 million years later, one of these lineages further divided, giving rise to the three modern periodical cicada groups: Decim, Cassini, and Decula.

Early American colonists in Massachusetts were struck by the sudden appearance of periodical cicadas, likening them to biblical locust plagues. This association led to the incorrect use of the term “locust” for cicadas in North America.

In the 19th century, entomologists like Benjamin Walsh, C.V. Riley, and Charles Marlatt studied cicadas’ unique biology. They found that unlike locusts, cicadas don’t damage crops or swarm.

Instead, they live mostly underground, feeding on plant roots through five juvenile stages.

Their synchronized emergences follow a 17-year cycle in the North and a 13-year cycle in the South and Mississippi Valley, with distinct regional groups known as broods.

Each color on this map indicates a 13-year or 17-year cicada brood, identified by University of Connecticut researchers during active cicada choruses. Broods XIII (brown) and XIX (orange) are set to emerge in 2024. Click on any point to view its corresponding brood information.

Source: University of Connecticut, used with permission.

Acting in unison

Magicicada’s notable trait is synchronous emergence in vast numbers, reaching up to 1.5 million per acre, enhancing their chances of mating.

This dense emergence offers a defense mechanism known as predator-satiation or safety-in-numbers. Predators like foxes, squirrels, bats, or birds consume their fill before exhausting the cicada population, leaving many survivors.

While periodical cicadas typically emerge on schedule every 17 or 13 years, occasional deviations occur, with a small group appearing four years early or late. Early emergence may result from favorable conditions promoting faster growth, while delayed emergence may stem from less favorable conditions.

With changing environmental conditions, such as climate warming, the ability to adjust their life cycle becomes crucial. If conditions prompt a large number of cicadas to emerge off-schedule by four years, they can still appear in sufficient numbers to satisfy predators and adapt to a new schedule.

Could climate change alter the timing of Magicicada emergence?

As glaciers retreated from the US 10,000 to 20,000 years ago, periodical cicadas established themselves in eastern forests. This led to a complex pattern of broods due to regional adaptations and temporary life cycle shifts.

Northeastern deciduous forests, where trees lose leaves in winter, are home to 12 broods of 17-year cicadas, while the Southeast and the Mississippi Valley host three broods of 13-year cicadas.

The distribution and timing of these cicadas’ broods are influenced by climate changes.

Research suggests the 13-year species Magicicada neotredecim, found in the upper Mississippi Valley, evolved during a past interglacial period about 200,000 years ago.

As temperatures increased, 17-year cicadas in this area shifted to a 13-year cycle.

Yet, human-induced environmental changes challenge the cicadas’ adaptability. While they thrive in forest edges and suburban areas, they struggle to survive deforestation or reproduce in treeless areas.

Some broods have disappeared over time, like Brood XXI in Florida and Georgia, Brood XI in Connecticut, and Brood VII in New York, which has shrunk to just one county since the 1800s.

Climate change may intensify these impacts. Warmer climates with longer growing seasons could lead more 17-year cicadas to adopt a 13-year cycle, akin to shifts observed in Magicicada neotredecim due to earlier warming.

Early emergences in recent years, such as in Cincinnati, Baltimore-Washington, and Chicago, hint at climate-driven changes.

In 2024, Brood XIII’s emergence will be near Brood XIX’s, but they won’t overlap. Previous mappings show they’re indistinguishable in appearance, song, and genetics in shared areas.

To monitor cicada distributions effectively over time, researchers rely on precise and high-quality data. Citizen scientists play a crucial role in this endeavor due to the vast populations of periodical cicadas and their brief adult emergence periods.

Those interested in contributing to the 2024 emergence documentation can download the Cicada Safari mobile app. By capturing and sharing photos, volunteers can participate in real-time research updates at www.cicadas.uconn.edu. If cicadas are present in your area, seize the opportunity to learn more about them and enjoy the experience!

Read the original article on: Science Alert

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