Forest Fridays: Cicadas
- by Guest Contributor
- May 31, 2024
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By Jason Ryndock
The appearance of the periodical cicada (genus Magicicada) is an extraordinary event that can evoke feelings of wonder. Their choruses that dominate the soundscape certainly remind us to pay attention to our oft-ignored six-legged neighbors.
Endemic to eastern North America, these cicadas occur in distinct broods with 13-year or 17-year life cycles. As if by magic, periodical cicadas suddenly materialize in a synchronous mass emergence, take flight on glittering, orange-veined wings, and sing in an exuberant ensemble just before a final disappearing act. Except for the occasional straggler, they are not heard again for well over a decade.
Image: Periodical cicadas are harmless and beautiful creatures. Photo by Katja Schulz, Wikimedia Commons.
How does a periodical cicada know when to emerge? A magician never reveals their secret; however, research demonstrates that they can count! Most of their life span (among the longest of insects) is spent underground as nymphs feeding on sap from the xylem of tree roots. Xylem transports water and dissolved minerals from the roots to the canopy, and every spring it becomes rich in amino acids. The nymphs tally these nutrient pulses to keep track of the years. As the soil warms in the spring of their final year, trillions emerge from the ground under the cover of darkness.
For about a month, males sing from morning to evening by vibrating a pair of corrugated, drum-like organs called tymbals. Muscles rapidly deform the tymbal membrane to produce sound, which is amplified by the male’s largely hollow abdomen. A chorus can reach an overwhelming 90+ decibels! Females do not sing but will audibly flick their wings to get a male’s attention.
This frenzy of courtship doesn’t go unnoticed by local wildlife, which gorge themselves on the defenseless cicadas, yet hardly make a dent. With predators satiated, many cicadas will live long enough to successfully mate, fueling their short adult lives with sap from woody plants. Females deposit eggs in V-shaped cuts in peripheral twigs of trees and shrubs. This causes damage known as flagging, but mature trees recover quickly and benefit from a deluge of dead cicada ‘fertilizer’. In six to seven weeks, the eggs hatch into nymphs, which drop to the ground and burrow, beginning the cycle anew.
Image: A cicada nymph must molt into an adult by shedding its exoskeleton, a highly vulnerable period. Photo by G. Edward Johnson, Wikimedia Commons.
Broods are composed of multiple species with the same life cycle. While the four 13-year species are generally southern and midwestern in distribution, all three 17-year species occur in Pennsylvania. The largest, Magicicada septendecim, has an otherworldly song. The smaller Magicicada cassini and
Magicicada septendecula call with various clicks and buzzes.
The emergence in 2024 is a special occasion. Two adjacent broods, the 17-year Northern Illinois Brood (XIII) and the 13-year Great Southern Brood (XIX) will emerge simultaneously. This hasn’t happened since 1803 when Thomas Jefferson was president! The double brood of 2024 will not occur in Pennsylvania, but we can look forward to Brood XIV in 2025! In the meantime, enjoy the summer songs of our ‘annual’ cicada species, whose adults appear every year.
About the Author: Jason Ryndock
Jason Ryndock is an Ecological Information Specialist with the Pennsylvania Natural Heritage Program, performing environmental review for the PA Department of Conservation & Natural Resources. His immersion in nature since childhood influences his research, creative pursuits, and hobbies. Through his passion for ecological restoration and native landscaping, Jason enjoys connecting people to the natural world.
