Those who live in many parts of the eastern United States will experience an odd phenomenon every 13 or 17 years. Depending on where you live, insects called cicadas emerge from the ground in huge numbers. But don’t worry. They don’t hurt people or pets. They’re just here to party.
It’s one of the loudest insect parties you’ll ever see — or hear. When large numbers of the adult insects convene, the collective noise made by males can approach 90 decibels. That’s about the same as a gas-powered lawn mower.
“Where the cicadas emerge, it will be spectacular,” Michael Raupp told Science News for Students in 2013. He’s an entomologist at the University of Maryland in College Park. Across some small areas, cicada concentrations may approach 1 trillion insects per square mile. That’s like having nearly 4 million cicadas emerge from a patch of ground the size of your bedroom floor (but not all at once, of course).
There are more than 3,000 species of these insects. The best-known species in North America are periodical cicadas. These 5-centimeter- (2-inch-) long insects typically emerge from the ground once every 13 or 17 years. There are 15 different cicada broods, which emerge in a specific region of the country and are identified by a Roman numeral. The 2021 group, a 17-year variety, is called “Brood X.”
Periodical cicadas spend more than 99 percent of their life underground. There, they slurp nutrient-rich fluids from the roots of certain trees and shrubs. These underground young are known as nymphs. This immature stage resembles adults.
While latched onto roots, nymphs track the passage of time by noticing chemical changes in their meals. Early in the final springtime of their lives, the nymphs burrow escape tunnels to the surface. Then each insect will return to root level until the soil temperature reaches roughly 64° Fahrenheit (about 18° Celsius). At that point, the nymphs will surface again, climb out and promptly ascend the nearest tall object. There each molts one last time, becoming an adult.
“You see the insects in a mad, desperate dash for the trees so they can survive and mate,” Raupp said. “Birds and squirrels will be eating them. It’s life. It’s death. It’s romance. It’s a massive display of Mother Nature’s wonder — in my opinion, at its best.”
Adult cicadas live for only two to four weeks. During that brief time, they mate and then the females lay eggs in the tender young branches of trees. Those eggs hatch after a few weeks. The young drop to the ground. At once, each tiny nymph begins burrowing down to find plant roots to feed on.
You might think that large numbers of parasites slurping nutrients from the roots of trees and shrubs for an extended period would harm plants. And Raupp said, “It’s a wonder that we don’t see more damage.” But to date, research has not shown that the underground activities of cicadas cause significant damage to their hosts.
Overall, in fact, cicadas probably help the environment, not hurt it. Their burrowing churns up the ground, loosening the soil, noted Raupp. That not only helps air reach plant rootsbut also helps water percolate deeply.
Big and noisy, cicadas frighten especially squeamish people. “But chill out,” Raupp cautioned. Learn as much about them as you can. People should realize that they aren’t going to harm children or pets.
Power Words
More About Power Wordsbrood: A group of related animals that emerges in a specific region in the same year. Depending on the animal type, the collective group is sometimes also known as a year class.(verb) The act of guarding and/or incubating eggs.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
concentration: (in chemistry) A measurement of how much of one substance has been dissolved into another.
decibel: A measurement scale used for the intensity of sounds that can be picked up by the human ear. It starts at zero decibels (dB), a sound hardly audible to people with good hearing. A sound 10 times louder would be 10 dB. Because the scale is logarithmic, a sound 100 times louder than 0 dB would be 20 dB; one that’s 1,000 times louder than 0 dB would be described as 30 dB.
egg: A reproductive cell that contains half of the genetic information necessary to form a complete organism. In humans and in many other animals, ovaries produce eggs. When an egg fuses with a sperm, they combine to produce a new cell, called a zygote. This is the first step in the development of a new organism."
entomologist: A biologist who specializes in the study of insects. A paleoentomologist studies ancient insects, mainly through their fossils.
environment: The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature andhumidity (or even theplacement of things in the vicinity of an item of interest).
host: (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents. (v.) The act of providing a home or environment for something.
insect: A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.
molt: (v.) To cast or shed skin, exoskeleton or feathers, which will be replaced with new. (n.) The act of molting, or the thing that is dropped during molting.
nutrient: A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.
nymph: A stage in the life cycle of some insects in which the immature individual resembles the adult. As nymphs grow, they will molt, or shed their external “skeleton,” several times. Unlike butterflies, which have a dormant stage of life called a pupa before becoming adults, nymphs remain active and will directly enter adulthood after their final molt.
parasite: An organism that gets benefits from another species, called a host, but doesn’t provide that host any benefits. Classic examples of parasites include ticks, fleas and tapeworms.
percolate: The action of a liquid that gradually moves through a filter or porous material.
phenomenon: Something that is surprising or unusual.
shrub: A perennial plant that grows in a generally low, bushy form.
species: A group of similar organisms capable of producing offspring that can survive and reproduce.
square: (in geometry) A rectangle with four sides of equal length. (In mathematics) A number multiplied by itself, or the verb meaning to multiply a number by itself. The square of 2 is 4; the square of 10 is 100.
trillion: A number representing a million million — or 1,000,000,000,000 — of something.
variety: (in agriculture) The term that plant scientists give to a distinct breed (subspecies) of plant with desirable traits. If the plants were bred intentionally, they are referred to as cultivated varieties, or cultivars.
Citations
Map: A.M. Liebhold, M.J. Bohne and R. L. Lilja. Active Periodical Cicada Broods of the United States. 2013. USDA Forest Service Northern Research Station, Northeastern Area State and Private Forestry.
About Sid Perkins
Sid Perkins is an award-winning science writer who lives in Crossville, Tenn., with his wife, two dogs and three cats. He enjoys cooking and woodworking, and he really, really wants to get better at golf.
