You may have heard of a special entomological event happening this year. It’s true, a rare “double brood emergence” of periodical cicadas is happening in 2024. The last time this happened was in 1803 when Thomas Jefferson was the US president. Read on to learn more!
Brood XIII, called the “Northern Illinois Brood,” has a 17-year emergence cycle that includes three cicada species. It will appear in the Midwest with potential to show up in southeastern Iowa (see dark brown counties on USFS map). Brood XIX, also called the “Great Southern Brood,” has a 13-year emergence cycle that includes four cicada species. This brood has a larger geographic range, extending from the east coast to southeastern Iowa (see light blue counties on USFS map). There may be an overlap in occurrence for Broods XIII and XIX in central Illinois.
These periodical species belong to the genus Magicicada. They have red eyes, dark thorax, and dark orange wings that extend well beyond the abdomen. The annual cicadas have dark eyes, green patches on the head and thorax, and have larger, robust bodies.
The life cycle of periodical cycles is pretty amazing! Females cut Y-shaped slits into twigs of deciduous plants and deposit about 20 eggs at a time. Over her life, she will lay about 600 eggs. When the first instars hatch, they drop to the ground and enter the soil. Periodical cicadas spend about 99% of their life underground, and mostly at second instars. Nymphs use a piercing-sucking mouthpart to feed on the xylem of woody plants. They will spend 13 or 17 years underground depending on their brood cycle. As soil temperatures warm up during their emergence year, fifth instars come out of the soil and crawl up on plants or structures. They molt one last time into adults; they also feed on plant fluids for a few weeks. Watch a humorous video of periodical cicada life cycle here. With a large number of cicadas expected in some areas, it will be easy to spot the adults, nymphs, and cast skins (like the one attached to a tree from Miznova on Flickr).
Newly-formed male adults “call” to attract females for mating. The sound comes from a drum-like structure called a tymbal on the abdomen. By using muscle contractions, males can create sound in a chamber that can exceed 106 decibels (similar to a motorcycle!). Cicadas have species-specific calls or screams. Listen to several periodical cicada songs here.
Periodical cicada emergence has been happening in 2024 for a few weeks in southern states. Watch a fantastic video of current nymphal emergence happening in St. Louis this week! We expect nymphs to emerge when soil temperatures reach 64 degrees. Iowa reached the important temperature benchmark this week. If you want to contribute to “crowdsourcing” the 2024 emergence, please log your confirmations via iNaturalist (search for “periodical cicadas” to see real-time data). Dr. Matt Kasson at West Virginia University is documenting the range of a fungal pathogen that infects periodical cicadas. It will be obvious of the infection because the tip of the abdomen is white (Email: mtkasson@mail.wvu.edu or Twitter @ImperfectFunGuy).
Some places may have more than a million cicadas emerging and screaming at the same time. It promises to be an epic event this summer! Read a whole lot more about periodical cicadas here.
Erin Hodgson Professor
Dr. Erin Hodgson started working in the Department of Entomology, now the Department of Plant Pathology, Entomology, and Microbiology, at Iowa State University in 2009. She is a professor with extension and research responsibilities in corn and soybeans. She has a general background in integrated...