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Ask the expert: The cicadas are coming

Portrait of Hannah Burrack
Hannah Burrack

For the first time in more than 200 years, two broods of cicadas – Brood XIX, known as the Great Southern Brood, and Brood XIII, known as the Northern Illinois Brood – will emerge from the ground simultaneously. Hannah Burrack, professor and chair of the Department of Entomology at Michigan State University and EEB core faculty member, answers questions about this rare occurrence.

What are cicadas exactly?

Cicadas are insects with all the species found in North America belonging to one family called Cicadidae. Other relatives include leafhoppers and spittlebugs. There are over 3,000 known species of cicadas, but the ones that capture much of our attention are the periodic cicadas, which include seven of these species and are found in North America. For insects, they are large at 1 to 2 inches long, triangular-shaped with large eyes, small bristle-like antennae and four clear wings with distinctive dark veins.

Why do cicadas stay underground for so long?

For some of the periodic cicadas, the nymphs — which are the immature stage of cicadas — can stay underground for as little as one and up to 17 years. When we say periodic cicadas, what we mean is that several species have adapted to emerge together in synchronized cycles of either 13 or 17 years. While underground, cicada nymphs are using their straw-like mouthparts to draw sap from the roots of perennial plants, mostly trees. They need to feed on plants that will be in the ground for long periods of time because their developmental period is so long.

So, why do they take so long to develop? We think this is an evolutionary adaptation for these species to avoid being preyed upon. They all emerge during the same year around the same time, which overwhelms any animals or other insects that might eat them. It’s not uncommon during mass cicada emergences to see birds, rodents and other animals just stuffed and completely uninterested in trying to eat any more of the insects.

What's special about the cicadas this year?

This year, two large “broods,” which are a group of periodic cicadas that emerge during the same year, will emerge. One is a 13-year brood and the other is a 17-year brood. Together, these broods cover most of the eastern U.S. and are adjacent to each other — something that only happens once every 25 years or so. That means that a huge number of people across 17 states will experience a mass emergence and people in Indiana and Illinois may experience both broods at the same time. These two specific broods, the Northern Illinois Brood and the Great Southern Brood, will not emerge together again for another 221 years. 

Interestingly, there are four species of 13-year cicadas and three species of 17-year cicadas, and multiple species are present in each brood.

What's the difference between annual and periodic cicadas?

Annual cicadas or maybe more accurately, non-periodic cicadas, do not synchronize their emergence. There are some truly annual species of cicadas that have one-year life cycles, which include the “dog-day cicada,” which emerges in late summer, hence their name. Other cicada species can have life cycles of up to 11 years, all but one spent underground, but do not emerge en masse during the same year.

When will the cicadas come out in 2024?

Cicadas start emerging when the soil temperature is greater than 64 degrees Fahrenheit. In most of the range for the two broods, this should happen in April and May.

Where will the cicadas emerge?

You can find detailed emergence maps for all the periodic cicada.  Briefly, the Northern Illinois Brood is present in Iowa, Illinois, Indiana and Wisconsin. The Great Southern Brood is found in Alabama, Arkansas, Georgia, Indiana, Illinois, Kentucky, Louisiana, Maryland, Missouri, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee and Virginia. The best place to find cicadas when they emerge is in wooded areas or areas with established trees.

How long will the cicadas be around?

The emerging adult cicadas will be around a bit over a month. After that, they die.

Are cicadas harmful to humans, pets or plants?

Cicadas are not harmful to people or household pets. They are not poisonous and do not bite or feed on animals. Female cicadas lay eggs following mating in woody plants (it’s the males’ loud mating calls that you hear), and they prefer small branches and stems around the diameter of a pencil or marker. A single egg mass may not damage plants, but many egg masses could injure young trees or shrubs. Small perennial plants such as blueberries, grapes and ornamental shrubs with small stems and branches can be covered with remay garden cloth or row cover fabric to protect them from cicadas in areas experiencing mass emergences. Normal, non-periodic populations are not a pest concern.