How billions of cicadas coordinate their emergence

EVANSTON, Ill. — As cicadas begin to emerge throughout the South and Midwest in the United States, Northwestern University’s Jorin Graham is available to discuss how these periodical broods synchronize their behaviors.

Graham is a Ph.D. student in physics at Northwestern’s Weinberg College of Arts and Sciences, where he studies complex networks and network science. He is advised by Adilson Motter, the Charles E. and Emma H. Morrison Professor of Physics and director of the Center of Network Dynamics.

Graham can discuss the study of synchronization, how its related to cicadas and how their emergence might temporarily disrupt the food web. He can be reached directly at JorinGraham2025@u.northwestern.edu.

Comments from Graham:

“Periodical cicadas spend years living underground before emerging together to briefly mate and die. Upon hatching, cicada nymphs return to the ground and repeat the process. This curious behavior, in which billions of cicadas coordinate their behavior, is an example of synchronization.

“The study of synchronization is itself rooted in physics, often considered to have originated with Dutch physicist Christiaan Huygens’ studies of pendulum clocks in the 17th century. Synchronization is now recognized as an important behavior across many domains — from engineered systems like power grids, to biological systems such as neuron firing in the brain, to other ecological phenomena such as the coordinated production of fruit by oak trees. Remarkably, such synchronized behavior is commonly achieved without centralized planning or enforcement.

“So how do periodical cicadas coordinate their emergence? Each individual cicada counts the passing years based on annual cycles of xylem flows, a nutritious fluid in trees on which they feed. Cicadas that are born the same year will emerge with the rest of their brood 13 or 17 years later. However, a few cicadas, known as stragglers, miscount and emerge too early or too late. If these cicadas reproduce, their offspring would also emerge out of cycle and, eventually, the periodic cicadas would lose synchronization. Synchronization is preserved by predators, such as squirrels, who quickly consume cicadas that emerge at the wrong time. During normal emergence years, so many cicadas come out that predators can’t eat all of them, allowing the remaining cicadas to reproduce, thus sowing the seed for the next coordinated emergence.”