A brood awakening

Cicadas are small summertime insects that go mostly unnoticed in a typical year. But every 13 or 17 years, up to a billion brood cicadas will emerge, covering the region’s trees and shrubs and deafening neighborhoods with mating calls that can register at 100 decibels. No matter if you’re fascinated or annoyed by these insects, one thing is clear, the brood cicadas demand our attention.

What are periodical cicadas and what is a brood?

Cicadas that emerge every year are known as annual cicadas, while the ones that emerge every 13 or 17 years are referred to as periodical cicadas. The cicadas that emerge together on one of these 13 or 17-year cycles are called broods, but each brood consist of multiple cicada species and some can overlap. Because brood cicadas emerge only a handful of times each century, they are particularly difficult to study, so we don’t know exactly why the broods emerge at these two intervals.

Many researchers believe that the large-scale emergence of brood cicadas is a survival technique. The insect is hunted by many different species over the spring and summer, but by emerging in such large quantities, enough can survive to breed and produce the next generation. But for the survival method to work, brood cicadas must emerge at the same time. If any of the insects emerge early, their population will be spread out and they will be eaten to extinction.

There are seven species of periodical cicadas in North America, classified into 15 broods that emerge in different locations with different species, on one of the two-year cycles. Each brood is named in roman numerals by the order in which the brood appeared from when they first started being tracked. Here in the Chesapeake region, Brood X, the 17-year periodical cicadas, is the one to watch out for. It is the largest, most densely populated and widely distributed cicada brood in the region, with as many as 1.5 million cicadas per acre. During an emergence year, Brood X cicadas can be found from Illinois to Delaware and Michigan to Georgia. In the first half of the 21st century, you can expect to find the Brood X in 2004, 2021 and 2038.

What creatures eat cicadas?

Almost everything eats cicadas, including people. Birds, spiders, mammals and amphibians will travel the forest floor and search tree branches to gorge themselves on cicadas during a brood emergence. Even fish will be cruising the water looking to feed on the cicadas that land there (with anglers using cicada imitation lures to trick fish). People snacking on cicadas need only worry about their allergies: cicadas and shrimp are closely related and those allergic to shrimp might also be allergic to cicadas.

Are cicadas dangerous?

Cicadas are not venomous or poisonous. They will occasionally bump into people and pets but this is not an act of aggression. Cicadas only pose a danger to young trees and shrubs as the females will cut small slits in young branches to lay eggs. After hatching, cicada larvae will also burrow into the ground to feed on tree roots for the next 17 years, though the damage is minimal.

Do periodical cicadas impact the environment?

By emerging in such large numbers, periodical cicadas serve as a critical food source for a wide variety of predators. By moving throughout the soil cicada nymphs help transfer resources above and below ground by creating tunnels that aerate the dirt, making it easier for water and nutrients to be absorbed. As adults die and decompose, the carcasses act as fertilizer for the forest floor. The new nutrients will fuel plants to grow larger and feed more creatures even after the cicadas are long gone. The exact details of how periodical cicadas impact the environmental is still a bit of a mystery: after all, scientists only have the opportunity to study the impact of each brood every 13 or 17 years.

How should you prepare for a periodical cicada event?

Avoid using pesticides during a periodical cicada event, as they will not reduce the number of cicadas and will likely harm other beneficial insects and those higher up on the food chain. Wait to plant new trees and use fine mesh fabric to protect existing saplings. To support researchers studying cicadas, use the Cicada Safari app to help track cicada broods. Other than that, try not to let the noise get to you and enjoy the natural marvel.

Want to learn more about the plants and animals of the Chesapeake Bay region? Visit our Field Guide and explore the region’s wildlife.