When we think of the life cycle of most insects, we may say they hatch from an egg, go through changes until they are eventually an adult, mate, lay eggs and die. This may take place in relatively little time, or it may take up to a year. With the periodical cicada, it takes years (emphasis on plural) – 13 or 17, in fact – unhurried, but reliable metamorphosis. We also have an annual cicada, which sings its song every year.
You will likely see several news articles this year about the forthcoming hatch of Brood X, the largest 17-year brood. As we anticipate this event, I thought it timely to explain more about this unique insect with the help of Dr. Cliff Sadof, Purdue Extension entomologist, and author of the Purdue Extension publication, “Periodical Cicada in Indiana.”
Some call these insects locusts, but the correct term is cicadas. Periodical cicadas are about 1½ to 2 inches long, have black bodies, with reddish legs, wing margins and eyes.
This year’s 17-year brood may appear in all counties, but heaviest emergence will be in south-central Indiana. In this region, Allen County will also have a smaller 17-year brood emerge in 2023.
Periodical cicadas appear in the last part of May through June. “The incessant cadence of high-pitched, shrill sounds announces their presence,” said Sadof. “Only the males make this noise.” The female has a knife-like organ to slit or puncture twigs of woody plants, where she lays her eggs.
Dr. Timothy Gibb, Purdue Extension entomologist, wrote that audiologists have measured this sound in close range to be in excess of 100 and even up to 120 decibels, which is approaching the pain threshold of the human ear!
Sadof explained their unique life cycle. After laying eggs, the adults die. In about 6 weeks, the eggs hatch, and the nymphs drop to the ground, dig into the soil, and feed by sucking sap from tree roots. At the end of 13 or 17 years, depending upon the brood, the nymphs come out of the ground. They crawl up tree trunks, posts, or other objects, shed their last shell, and emerge as winged cicadas. Adults live about a month, during which they mate and each female lays between 400-600 eggs.
“While some people consider the mass emergence of cicadas one of nature’s many wonders, others find it a nuisance,” said Sadof. “In urban areas, heavy infestations can make the sidewalks and roads slick with dead insect carcasses.” He said cicadas do serious damage to young trees in fruit orchards and nurseries. Additionally, they lay eggs on over 200 woody tree species, including maple, redbud, dogwood, and oak. Rose and grape can also be affected.
“Small ornamental trees and shrubs can be protected by covering them with no larger than 3/8” mesh screening while cicadas are present,” said Sadof. This, along with selective planting and pruning times, are the primary cultural controls available.
Birds and squirrels will feed on cicadas, but they can only eat so many.
“The use of pesticides for controlling the cicada is controversial,” said Sadof. “Pesticide trials indicate that pesticide applications need to be repeated every 3-4 days to prevent oviposition [egg laying].” Sadof said this is typically not practical for the 6-week flight period, therefore cultural controls are recommended.
Branch dieback is one symptom of cicada damage.
I briefly mentioned annual cicadas in the opening. Annual cicadas, or “dog day” cicadas, come out later in the year, and legend says that after the first call of the cicadas in late summer, there will be six weeks until frost. (Remember, that’s folklore, not necessarily fact). Annual cicadas have black eyes rather than the red ones we find on periodical cicadas.
Find Sadof’s publication at www.edustore.purdue.edu.