C
icadas are a fascinating group of insects known for their distinctive life cycles, particularly the periodical cicadas that emerge in synchronized, large-scale events every 13 or 17 years. In Northern Wisconsin, the 17-year cicada, known as Magicicada septendecim, captures the interest of entomologists and the public alike with its remarkable and predictable emergence patterns.
The 17-year cicadas in Northern Wisconsin spend the vast majority of their lives underground as nymphs, feeding on the sap of tree roots. This subterranean phase is an extended developmental period that can span precisely 17 years. The long underground duration is thought to be an evolutionary strategy to avoid predators and ensure survival through generations.
As the 17th year approaches, these nymphs undergo significant physiological changes in preparation for their emergence. Soil temperature plays a critical role in signaling the cicadas to surface. When the ground warms to about 64 degrees Fahrenheit, typically in late spring, millions of nymphs simultaneously tunnel to the surface, marking the beginning of their short-lived adult stage.
Once above ground, the cicadas shed their nymphal exoskeletons and become winged adults. This transformation is often accompanied by a period of increased vulnerability, as the cicadas are soft and unable to fly immediately after molting. Within a few hours, their new exoskeletons harden, and the adults can take to the trees.
The adult phase of the 17-year cicada lasts only a few weeks, during which their primary focus is on reproduction. Male cicadas are known for their loud and distinctive mating calls, produced by rapidly vibrating membranes called tymbals on either side of their abdomen. These calls serve to attract females and are a hallmark of the cicada emergence, often reaching deafening volumes in areas with high cicada densities.
After mating, female cicadas lay their eggs in slender tree branches, making small slits in the bark to deposit their eggs. This process can cause some damage to young trees, but it generally does not pose a significant threat to established trees. The eggs hatch after about six to ten weeks, and the newly emerged nymphs drop to the ground, burrowing into the soil to begin their long underground development cycle anew.
The mass emergence of cicadas provides a temporary but significant food source for a variety of predators, including birds, mammals, reptiles, and even other insects. This predator satiation strategy ensures that, despite the high predation rates, a sufficient number of cicadas survive to reproduce and continue the cycle.
The emergence of 17-year cicadas is not only a natural spectacle but also holds cultural and ecological significance. For local communities, these events often become a topic of interest and even celebration. In Northern Wisconsin, cicada emergences can draw attention from nature enthusiasts, scientists, and photographers eager to document and study this rare event.
Ecologically, the cicadas’ life cycle contributes to the health of forest ecosystems. The decaying bodies of cicadas after their brief adult phase provide a nutrient boost to the soil, enhancing plant growth and contributing to the overall fertility of the environment. Additionally, the natural pruning effect of egg-laying can promote new growth in trees and shrubs.
If you have questions about periodical cicadas or want to report a sighting, please visit the University of Wisconsin-Madison Periodical Cicada webpage. https://cicadas.wisc.edu/