Learn about the 17-year periodical cicadas that emerge from underground to shed their nymph exoskeleton before mating begins.
Brood X, or the Great Eastern Brood, is the arrival of the species of cicadas that surfaces every 17 years and fills the air with their deafening mating hum that can reach up to 100 decibles. This event starts in May and lasts five to six weeks. Besides their irritating noise, it will be hard to miss their crunchy discarded skeletons that will literally be everywhere. States that will play host to this event are Delaware, Georgia, Illinois, Indiana, Michigan, Maryland, North Carolina, New Jersey, New York, Pennsylvania, Tennessee, Virginia, Kentucky, West Virginia and Washington, D.C.
17-Year Periodical Cicada Species
These cicadas are periodical cicadas and are not to be confused with the annual cicadas that appear every year, usually in July or August. Folk legend has it that when you hear the song (or noise, depending on how you look at it) of the annual cicadas, there will be six weeks until the first frost.
To date, there are 190 varieties of this creature identified in North America and some 3,390 different species found around the world. However, this number grows as researchers discover new species. In the United States, there are two predominant periodical kinds, the 17-year cicadas that are found primarily in the northern and eastern United States and the 13- year ones that emerge in the southern states.
Often confused with locusts, cicadas are a completely different species. Locusts are actually short-horned grasshoppers.
Cicadas Used in Food and Medicine
Cicadas are mainly a nuisance as opposed to being dangerous. They fly into windshields and their carcasses litter just about everywhere. They don’t bite or sting and are not poisonous although their sound has been documented as being loud enough to cause permanent hearing loss in humans.
These strange creatures have been used as money and as ingredients in folk medicine. They are still part of the Chinese, Latin American and central African diets. In 2011, cicadas were used in part of a batch of ice cream at Sparky’s Homemade Ice Cream in Columbia, Missouri. This only lasted through one batch as they did not become a favorite!
Cicada Lifecycle
These insects are pretty unique creatures. They have a head, thorax and an abdomen. They begin their lifecycle as rice-shaped eggs. Adult females lay their eggs in a groove of a tree limb. This groove provides shelter and also exposes tree fluids that the young cicadas feed on. These grooves can kill small branches.
The young look like termites or small white ants once they hatch from the eggs. They feed on the tree fluids until they are ready for their next cycle where they crawl from the groove and fall to the ground. From here, they dig underground until they find roots to feed on. Usually, they start on grass roots and work their way up to the roots of the host tree. Depending on the species, they stay underground from two to 17 years where they remain active tunneling and feeding.
When ready, they emerge aboveground as nymphs and climb the nearest available vertical surface, usually a plant. They usually all emerge at once — for quite a sight! On the plants, they start to shed their nymph exoskeleton. After free of this, their wings inflate and fill with fluid. Both nymph and adult forms have beaks which they use to suck fluids called xylem from plants. This is how they feed and drink.
The Cicada Song
After they have wings, they are ready to start their brief adult life. Adults spend their time in trees looking for mates. This is where the “noise” comes into play. The males sing, or “vibrate,” the females respond, mating begins and another cycle of life begins anew.
They sing by flexing their tymbals, which are drum-like organs found in their abdomens. Small muscles rapidly pull the tymbals in and out of shape. The sound is intensified by their mostly hollowed out abdomens. Females and some males also make sound by flicking their wings, however this is not the sound that cicadas are known for.
Why Every 17 Years?
So, what’s the strange phenomena behind the 17-year emergence cycle of some species? It is actually part of the cicada evolutionary cycle that dates back 1.8 million years. Summers could be cold and, if it gets below 68 degrees Fahrenheit, it is too cold for them to mate and survive. Ironically, they can’t survive cold summers above ground but below ground is fine. Thus, they evolved different cycle lengths to improve the odds of survival.
Still, why 17-year intervals, why not 18 or 20? Scientists have no definite answers but they do have a couple theories. One is that the unusual prime-numbered cycle prevents them from run-ins with the life cycles of certain wasps that prey upon them. Another hypothesis is that this odd-year emergence reduces the likelihood that cicadas will mate and hybridize with different species, thus improving the survival chances of their own kind.
Not all areas in all of the 15 states will be able to see them. There are certain regions where they are found in each state. If you are in an area where they will be, you will want to cover newly-planted trees and shrubs with netting because they can severely damage young trees. Besides this, they pose no danger and they will only be here for a short while so don’t try to harm them.
Instead, on just the right spring day when the temperature reaches 64 degrees Fahrenheit, the nymphs will all burrow to the surface and make a mass emergence all at once, to the tune of 1.5 million to an acre of ground. Wow, that will be something to see!
Lois Hoffman is a freelance writer and photographer covering rural living with more than 20 years of experience, contributing to Successful Farming, Country, and Farm & Ranch Living. She lives on a 37-acre hobby farm in Pennsylvania.
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