Cicadas are Coming!
Cicadas are coming!
In 2024, two distinct cicada broods, Brood XIII and Brood XIX, will simultaneously emerge—an occurrence not witnessed since 1803. Brood XIII, on a 17-year cycle, and Brood XIX, on a 13-year cycle, represent rare instances of synchronized emergence, highlighting an unusual event in the life cycle of periodical cicadas.
These cicadas are systematically categorized into broods using Roman numerals, a system established by entomologist Charles Lester Marlatt in 1907. He identified 30 broods, with those on a 17-year cycle generally found further north compared to their 13-year counterparts.
Figure 1. Periodical cicadas. Photo by Gene Kritsky of Mount St. Joseph University
John Cooley, Ph.D., an associate professor at the University of Connecticut, notes that of the thousands of cicada species, fewer than ten species exhibit this periodic emergence. The overlap of these two specific broods occurs narrowly, centered significantly in Illinois, where Brood XIII emerges in the northern half, and Brood XIX in the southern.
Why 13 and 17 years?
The extended juvenile phase of these cicadas, spanning 13 or 17 years, serves as an evolutionary adaptation for predator evasion. The use of prime numbers in their life cycles—13 and 17 years—complicates synchronization for predators with shorter reproductive cycles, effectively disrupting predation patterns.
Figure 2. Periodical cicadas in Brood XIII, on a 17-year-cycle, and Brood XIX, on a 13-year-cycle, will emerge in 2024 in the same year for the first time since 1803. Their ranges are contiguous but do not overlap; collectively they’re expected to appear in parts of up to 18 states, mostly in the Midwestern U.S. Illinois is at the epicenter of the dual emergence, with Brood XIX in the southern half of the state and Brood XIII in the north. (Image by Gene Kritsky of Mount St. Joseph University.)
Furthermore, by coordinating their emergence to occur simultaneously in massive numbers, the cicadas enhance their chances of survival, as the sheer volume of individuals can overwhelm and confuse predators.
Figure 3. Table of periodical cicadas. (Photo by https://en.wikipedia.org/wiki/Periodical_cicadas).
Life as a Cicada
Periodical cicadas spend the majority of their life underground as nymphs, within approximately two feet of the surface, feeding on plant root sap. They undergo five developmental stages in this environment. The nymphs dig deeper as they mature, eventually surfacing when soil temperatures signal the right conditions for their final molt into adulthood. Upon emergence, typically between late April and early June, mature nymphs construct exit tunnels. Following their emergence, they undergo a final transformation on suitable vertical surfaces. After a brief period of maturation, they enter a short adult phase dedicated solely to reproduction. Males produce loud mating calls to attract females, forming dense groups that amplify their collective sound, facilitating mating.
Ecological Impact of Cicadas
Ecologically, cicadas are benign to humans and most wildlife, lacking defensive mechanisms like stings or bites. However, their life cycle significantly impacts local ecosystems. For example, tree growth can decline due to the nymphs' extensive root feeding prior to emergence. Predator species like moles and wild turkeys experience population fluctuations tied to the cicada life cycle, benefiting from the abundance of food during emergence years but facing food shortages afterward. After the cicadas die, their bodies decompose, enriching the soil with nutrients and impacting the broader forest ecosystem.
Figure 4. USDA Forest Service map of periodical cicada brood locations by county and timing of next emergence (as of 2024)
References
Bernhardt, C. (2024, April 25). Periodical cicadas, 2024: Entomologists prepare for the six-week serenade. Entomology Today. https://entomologytoday.org/2024/04/25/periodical-cicadas-2024-broodxix-xii-entomologists-prepare-six-week-serenade/
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