Periodical cicada emergence disrupts food webs, increases plant damage in eastern North American forests

The periodical mass emergence of cicadas in eastern North American forests can “rewire” forest food webs and initiate a cascade of ecological impacts that propagates throughout the food chain, according to a study that quantified effects of the 2021 Brood X cicada emergence. The study found that when insect-eating birds have abundant prey in the form of cicadas and thus shift their focus away from their usual repast – leaf-eating caterpillars – the caterpillars feast more heavily upon the leaves of oak saplings, doubling insect leaf damage. “Although previous studies have documented strong ecological impacts that result from the direct consumption of pulsed resources,” say the authors, “our results highlight the need to consider the additional effects stemming from the organisms that escape predation during pulses.” Once every 13 to 17 years, billions of cicadas concurrently emerge from the soils within eastern North American forests. Although periodical cicada emergences in the eastern U.S. are among nature’s largest and most dramatic biomass pulses, the ecological consequences of these events aren’t fully understood. To better understand how periodical cicadas affect trophic dynamics, Zoe Getman-Pickering and colleagues quantified the effects of the 2021 Brood X cicada emergence by combining field observations of avian foraging during the 2021 emergence and tree-based experiments in the years before, during and after the event. Getman-Pickering et al. report that the emergence resulted in community-wide shifts in bird predation and found that 82 bird species across the study area opportunistically changed their foraging style to include the newly emerged cicadas. This shift resulted in a measurable decline in bird predation on oak-feeding forest caterpillars, which are consumed in large numbers during a typical year by insect-eating birds. According to the findings, reduced predation led to a doubling of both caterpillar densities and herbivory rates on oak saplings during the emergence year. Taken together, the findings demonstrate that the cicada-driven shift in avian foraging resulted in a cascade that affected multiple trophic levels and increased plant damage. “Pulse events in general, including both insect outbreaks and climatic extremes such as heat waves, are helpful teaching moments because they can reveal ecosystem response to chronic stressors,” writes John Parker in a related Perspective.

The authors' website with free, digitally available educational materials can be found at www.friendtocicadas.org