Spring 2024 marks a biological event so rare that the last time it occurred, Thomas Jefferson was the President of the United States. Trillions of periodical cicadas are emerging simultaneously across the American Midwest and Southeast. This dual emergence brings together Brood XIII and Brood XIX for the first time since 1803, creating a loud, chaotic, and fascinating natural spectacle that will not happen again for another 221 years.
Periodical cicadas are unique to North America and are distinct from the annual cicadas that appear every summer. These insects, belonging to the genus Magicicada, spend the vast majority of their lives underground feeding on tree root sap. They emerge only to molt, mate, lay eggs, and die.
The 2024 event is mathematically significant because of the specific life cycles involved:
Because 13 and 17 are prime numbers, their life cycles align very rarely. They sync up only once every 221 years (13 multiplied by 17). The last co-emergence was in 1803, and after the 2024 season concludes, these two specific broods will not appear together again until the year 2245.
While “trillions” sounds like a terrifying number to some, the emergence is geographically contained. The two broods occupy adjacent territories with a small strip of overlap.
This 17-year brood is heavily concentrated in the Midwest. If you live in or visit the following areas, you are likely seeing the highest density of these insects:
The Great Southern Brood covers a much larger geographic footprint. It is the largest of all 13-year broods and spans across at least 15 states:
The most scientifically interesting area in 2024 is Central Illinois. In a narrow band covering counties like Sangamon (Springfield), Macon, Logan, and McLean, the ranges of the two broods abut and overlap slightly. Scientists from institutions like the University of Connecticut and the University of Illinois are studying this zone to see if the 13-year and 17-year species interbreed, though genetic differences usually prevent this.
The emergence begins when the soil temperature reaches exactly 64 degrees Fahrenheit at a depth of about eight inches. This usually happens in late April for the southern states and mid-to-late May for the northern states.
Once the temperature trigger is pulled, the process unfolds rapidly:
It is important to clarify that periodical cicadas are not locusts. They do not have chewing mouthparts capable of stripping leaves or destroying crops. They drink plant fluids through a straw-like beak.
The emergence is a massive energy transfer from underground to the surface.
While they do not eat leaves, female cicadas can damage young trees. The female uses an ovipositor to slice into small branches (about the width of a pencil) to lay her eggs. This can cause the tips of branches to brown and wilt, a phenomenon known as “flagging.” Mature trees tolerate this natural pruning easily, but saplings or newly planted ornamental trees should be covered with netting (mesh size 1⁄4 inch or smaller) to prevent damage.
The sheer scale of the 2024 emergence has highlighted some of nature’s stranger phenomena.
A portion of the population is infected by a fungus called Massospora cicadina. This fungus contains psilocybin (found in magic mushrooms) and cathinone (an amphetamine). The fungus consumes the cicada’s abdomen and reproductive organs, replacing them with a chalky white plug of fungal spores.
Despite losing the lower half of their bodies, these “zombie cicadas” remain active. The fungus manipulates their behavior, causing males to mimic female wing-flick signals. This attracts other males, who attempt to mate with the infected host, thereby spreading the spores further.
While standard Magicicada have intense red eyes, a rare genetic mutation results in blue or greyish-white eyes. During the 2024 emergence, a verified blue-eyed female was found in the Chicago area and donated to the Field Museum for DNA sequencing. These are incredibly rare, appearing in perhaps one in a million insects.
Do cicadas bite or sting? No. They do not have stingers or jaws for biting. They are harmless to humans. Their feet can feel prickly or sticky if they land on you, but they cannot hurt you.
Is it safe for my dog to eat them? Generally, yes. Cicadas are not toxic and are high in protein. However, the hard exoskeletons are difficult to digest. If a dog eats too many, it may cause vomiting or stomach upset.
How long does the noise last? The adult lifespan is roughly four to six weeks. Once the males die, the noise stops. The entire event typically concludes by late June or early July, depending on how early the spring warm-up began.
Will they enter my house? Cicadas are clumsy fliers and do not seek out indoors. They may accidentally fly through an open door or window, but they are not trying to infest your home like ants or roaches. They require soil to complete their lifecycle.
When is the next time this double brood happens? Brood XIII and Brood XIX will not co-emerge again until the year 2245. However, different broods emerge in different regions almost every year. For example, Brood XIV is scheduled to emerge in 2025.