The big news last week pertained to the cancellation of President Biden’s first trip abroad because flying insects had filled his airiplane’s engines, grounding it and forcing the president to seek another way to travel. This was inevitable with the billions of cicadas flying around the eastern United States in recent weeks.  

The periodic cicadas of the genus Magicicada Homoptera: Cicadidae now fluttering, crawling and singing from trees there have been one of the country’s longest scientific traditions.  They have fascinated biologists since they were first discussed in the scientific literature over 300 years ago. Many well-known 19th century naturalists, including Charles Darwin, Asa Gray and Joseph Hooker, entered into discussions concerning the specific status of the 13- and 17-year forms.

Central to this interest in periodical cicadas is their prime-numbered life cycle and amazing periodic, synchronized appearance in almost unbelievably large numbers. The evolution of a long life cycle combined with perfect synchronicity allows Magicicada spp. to escape the build-up of predators.

Although periodical cicadas are not the longest-lived insects, they may have the longest juvenile development. Periodical cicada nymphs feed underground on root xylem fluids for 13 or 17 years. From late April to early June of the emergence year, fifth-instar nymphs emerge from the ground, crawl upward, and develop into adults, which are active for about four to six weeks. Within the first two weeks of the mass emergence, adults aggregate in chorus centers, i.e. places where males sing and mating takes place. The females lay eggs in pencil-sized twigs of trees, and after six to eight weeks, nymphs hatch and rain down to the ground. There, nymphs rapidly enter the soil and begin feeding on small rootlets. Nymphal mortality can reach 98% in the first two years.

As they grow, nymphs apparently move deeper below ground, feeding on larger roots. The insects molt (shed its exoskeleton) four times before emerging when the ground temperature reaches roughly 17.7 C (64 degrees F).   

This is the moment when they surface in droves — up to 1.4 million cicadas per acre — to molt into their adult form, sing their deafening love song and produce the next generation before dying just a few weeks later.

Broods

Nearly 3,400 species of cicadas exist worldwide. But periodical cicadas that emerge en masse once every 17 or 13 years are unique to the eastern U.S. The 17-year cicadas live in the North, and the 13-year cicadas are found in the South and the Mississippi Valley. The three species of 17-year cicadas —Magicicada septendecim, M. cassinii and M. septendecula — form mixed-species cohorts called broods whose members arise like clockwork on the same schedule.

The broods are identified by Roman numerals. Brood X is the largest of the 12 broods of 17-year cicadas, which emerge in different years.  It is the enormous brood currently serenading much of the East coast now and the same one known to dominate the area around Cincinnati. Brood X previously emerged in 2000, four years early. The cicadas overwhelmed predators, leaving them to survive and mate. Then 17 years later the group emerged a second time, having spread in geographic range, and likely formed a new brood.

Continued Research

Despite years of study scientists still have no idea about what is occurring with the insects while they are underground or how new populations are formulated.  

Fortunately, there is now a new free app called Cicada Safari to help. There are 150,000 people using it, and they have uploaded geotagged photos of cicadas.  This should help solve the mystery.  The public can use the app, released in 2019 by Gene Kritsky, an entomologist at Mount St. Joseph University, to send photos to researchers, who review the genus, location and brood identity of the cicadas.  

Last year, Cicada Safari data showed that not one, but four broods of periodic cicadas emerged off cycle.  Stragglers can emerge years before or after their brood.  Without the public, the full scope of last year’s straggler event would likely have been missed. More and more people than ever are using the app during the pandemic. Between 2019 and 2020, Cicada Sarfari’s user base grew by nearly 50%.  

Last year also marked the first scientific paper published based on Cicada Safari’s data. It cross referenced air temperature with nymph emergencies reported through the app. The aim was to improve predictions of cicada emergencies using air temperatures, which are far more available than using soil temperatures.  It is possible that warm winters may cause cicadas to emerge in the wrong year.

Final Thoughts

Some of the best photos of cicadas I have ever seen are available on the Cicada Safari app. There is also a map with current sightings of cicadas.  The most recent was east of Angola and south of Highway 20.

Max Sherman is a medical writer and pharmacist retired from the medical device industry.  His new book “Science Snippets” is available from Amazon and other book sellers. It contains a number of previously published columns.  He can be reached by email at  maxsherman339@gmail.com.