Cicadas in the USA: Why there are so many this year

There are over 3,000 species of cicadas worldwide. They spend most of their lives as larvae in the soil. Only after they are fully grown do they come to the surface of the earth to feed. For many cicada species this occurs annually, for others every 13 or 17 years. Scientists have long been puzzled as to why cicadas emerge in prime numerical intervals, but there is no obvious evolutionary biological explanation for this.

There have been a few calls about sirens or a screeching or roaring sound in the air.

Its 17-year rhythm, called Prud XIII, will soon arrive in the US Midwest. In a small area in central Illinois, their migration range may overlap with that of the XIX Prud.

John Lill, a biologist from George Washington University, explains the fact that cicadas appear in large flocks because individual animals are practically defenseless and are easy prey for birds, turtles, raccoons and other predators.

Lill and colleagues recently found that the emergence of Brut X in Washington, D.C., in 2021 led to an increase in insectivorous birds. Because the birds wanted to eat the cicadas that appeared in large numbers, there were more caterpillars. This led to more oak shoots being eaten by the caterpillars.

Other new research has found that oak trees produce particularly high numbers of acorns two years after the cicadas migrate. This means that there are many mammals that eat acorns, such as wild boars. It also increases people's risk of developing tick-borne Lyme disease.

This shows that the ecological impact of the appearance of cicadas can last years after they disappear, Lill says.

Changes in nature by humans sometimes have positive effects on cicadas. Well-lit trees in suburban gardens provide optimal conditions for spawning. When the adults die, the cicada larvae hatch from the eggs, drop from the trees and burrow into the ground, starting the cycle again.