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Cicada Apocalypse

April 29, 2024

Humans are capable of effective communication in a room where many people are loudly talking all at once, a phenomenon known as the cocktail party effect. Communication between computers is more limited, since a collision of two or more devices sending data at the same time prevents any data transfer. Data transfer in the early days of computing was by a simple serial interface known as RS-232, and collisions were avoided using signals known as RS-232 RTS/CTS for Request To Send and Clear To Send. These were sent on individual signal wires; and, later, the IEEE 802.11 RTS/CTS protocol was developed for wireless networking. WiFi now uses a collision avoidance protocol known as carrier-sense multiple access with collision avoidance (CSMA/CA)

9-pin male serial port connector

A 9-pin male serial port connector, once ubiquitous on desktop computers and laptop computers, but rarely seen today.

Rarer still is its 25-pin ancestor, the only connector specified in the original RS-232 standard. (Wikimedia Commons image)

The cicada, an insect of the order Hemiptera, has about 2500 species worldwide. One curious genus, the Magicicada, is native to North America, and it has an adaptation to collision avoidance of two variants. These cicadas remain in a dormant underground nymph form for long periods, with one emerging every 13 years, and the other every 17 years. Thirteen and seventeen are prime numbers, and the smallest composite number with which they divide is 221.

This means that these variants will simultaneously emerge every 221 years. The last such emergence was in 1803, and the next will be this year.[1-3] More than a trillion cicadas are estimated to emerge in the contiguous United States this year, and there might be as many as 1.5 million per acre.[2] In 2024, the 17-year variant will emerge geographically adjacent to the 13-year variant, but little overlap is expected; so, no cicada apocalypse.[2]

A North American cicada.

A North American cicada.

My children would discover nymphd of these during their backyard excavations of our Northern New Jersey home.

(U.S. Bureau of Labor Statistics image. Click for larger image.)

Aristotle (384 BC-322 BC) devoted a few paragraphs of his History of Animals (4th century BC) to the cicada.[4]
The cicada is not found where there are no trees... They lay their eggs in fallow lands... The grub, on attaining full size in the ground, becomes a tettigometra (or nymph)... It is the male that sings, and the female that is unvocal... the creature is so weak-sighted that it will take to climbing your finger as though that were a moving leaf.[4]
Cicadas have been a part of human culture for most of human history for their song and as a delicacy. While Aristotle wrote about the sweetness of cicadas when eaten, the US Food and Drug Administration warns that cicadas should not be eaten if you're allergic to shellfish. Because of their song, they were considered sacred to Apollo, the god of music and other skills, by both the ancient Greeks and Romans. The cicadas were also a symbol of resurrection and immortality.

It's theorized that the Magicicada genus of North American cicadas developed its 13/17 year cycle as an adaptation against predators. First, the long emergence times make them an unreliable food source; so, no predator would evolve to use them as an exclusive source of food. Second, their simultaneous emergence in huge numbers makes it more likely that members of each variant will survive predation to reproduce. Additionally, the staggered emergence of the two variants ensures that they do not compete for the same food sources for centuries at a time.

Geographic distribution of periodical cicada broods.

geographic distribution of periodical cicada broods.

Broods I–XIV are the 17-year cicadas, and brood XIX is the 13-year cicadas.

(Image from fig. 1 of ref. 5,[5] adapted from C. L. Marlatt, "The periodical cicada. Bulletin of the USDA Bureau of Entomology, vol. 71 (1907), pp. 1-171, and C. Simon and M. Lloyd, "Disjunct synchronic populations of 17-year periodical cicadas: relicts or evidence of polyphyly?," Journal of the New York Entomological Society, vol. 90 (1982), pp. 275-301. Click for larger image.)

As can be seen from the above figure, entomologists have organized cicada into broods. Brood XIII, 17-year cicada found mainly in Wisconsin, Iowa, and Illinois, and Brood XIX, 13-year cicada found in the Southeastern and Midwestern United States, will emerge simultaneously in late April through June of this year, and may overlap in Illinois.[1-2]

One question is how the cicada count years. It's conjectured that it's the annual cycle of the fluid in the trees on which the nymphs feed.[1] That would explain the year of emergence, but the cicadas, which emerge when the ground temperature is about 18 °C, emerge collectively although the temperature varies across terrain.[1] It's conjectured that the simultaneous emergence is triggered by pheromones, or by sound.[1] In my opinion, it's likely the sound of the first cicadas waking the others, since their song, produced in males by abdominal membranes, is quite intense. A female cicada will lay hundreds of eggs in small tree branches after mating; later, cicada nymphs will fall from the trees to burrow underground.[2] Climate change may eventually change a greater number of 17-year cicadas into 13-year cicadas.[2]

A nymph of the 17-year cicada

A nymph of the 17-year cicada.

After hatching, the nymphs burrow into the ground, where they suck sap from tree roots.

(Wikimedia Commons image by the United States Department of Agriculture. Click for larger image.)


  1. Sophia Chen, "This Spring, the Cicadas Are Gathering Like It’s 1803," APS News, vol. 33, no. 3 (March 15, 2024).
  2. John Cooley and Chris Simon, "Billions of cicadas are about to emerge from underground in a rare double-brood convergence," The Conversation, April 18, 2024.
  3. Korey Morgan, "Cicadas stir up a ruckus," USDA Forest Service, Office of Communication, May 19, 2021.
  4. Aristotle, "The History of Animals," D'Arcy Wentworth Thompson, Trans., University of Chicago Penelope by Bill Thayer.
  5. Walter D. Koenig, Andrew M. Liebhold, Jalene M. LaMontagne, and Ian S. Pearse, "Periodical Cicada Emergences Affect Masting Behavior of Oaks." The American Naturalist, vol. 201, no. 5 (May, 2023). A PDF file is available at the US Forest Service website, here.

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