NASHVILLE, Tenn. (WKRN) – After 17 years underground, the periodical cicadas, known as Brood X, are starting to emerge in areas of Middle Tennessee.
What’s the difference between a periodical cicada and an annual cicada? We break down the facts.
Periodical cicadas have red eyes, black bodies, red/orange veined wings and legs. They are smaller than annual cicadas. Adults grow up to 3/4 to 1 and 1/4 inches long.
Annual cicadas, also known as dog-day cicadas, are generally larger. Adults grow up to 1 and 1/3 inches long. They have dark green to black bodies and green veined wings.
According to Dr. Gene Kristsky with Mount St. Joseph University, “The periodical cicadas tend to come out in May and June. The annual cicadas tend to come about towards the end of June, into July, and the rest of the summer.”
Once annual cicadas emerge, they begin to mate and lay eggs about two weeks later. Each female can lay between 400 and 500 eggs. Those eggs will hatch between one and a half to two and a half months later. The nymphs then burrow into the ground feeding off roots. About two years later the nymphs emerge and molt into adults.
Periodical cicadas have a similar above-ground life cycle. However, the nymphs remain underground for either 13 or 17 years.
The Song of the Cicadas
Only the male cicada produces the mating call to attract females. They use organs called the tymbals to produce the sound. The sound runs around 90 decibels, which is equivalent to a lawnmower. Females use wing flicks to respond to the mating call.
Some species of cicadas don’t have tymbals and use their wings. That process is called crepitation. Others use a process called vibrate the substrate, which means they vibrate the ground to make noise rather than the air.
Periodical cicadas come out in larger numbers, which means, their singing could be heard from miles away.
13 vs. 17 Year Periodical Cicadas
There are 30 broods of periodical cicadas in the United States. With the 17 year variety primarily emerging in the Northeast and the 13 year variety emerging in the South. However, brood ranges overlap in the southern Appalachian region.