In two previous episodes we learned about the somewhat surprising appearance of vast numbers of periodical cicadas in the Washington metropolitan region. While dashing to class to give a final exam last Thursday, I was delighted to hear a magnificent chorus of periodical cicadas in the treetops of the UMD campus. Several folks have asked what the ruckus in the treetops is all about and how cicadas make this sound. I presented an explanation for this acoustic extravaganza in a previous episode about Brood II back in 2013. Here is an updated excerpt from that episode:
“During the past two weeks, cicada nymphs vacated the earth through their exit tunnels and dashed to vertical structures to shed their nymphal exoskeletons and emerge as adults. Within hours of this remarkable transformation, the adult’s appearance changes from pale white to jet black as its exoskeleton hardens. Males and females quickly climb to the treetops to begin their courtship ritual. Male cicadas require from five to eighteen days before they begin calling and enter the mating game.
While cicadas continue to emerge from the earth, chorusing of thousands of cicadas in nearby treetops produces other-worldly sounds.
To make the sounds necessary to woo a mate, male cicadas evolved unique structures called tymbals. These paired organs are located on the sides of their bodies just beneath the wings. Muscular contractions vibrate the membranous tymbals much like a drumhead to produce sound. The sound produced can be prodigious! Recorded at 90 decibels or more, this is as loud as a lawn mower engine or jet aircraft passing overhead. Males produce a variety of calls for different purposes. If threatened by a predator such as a bird or a squirrel, a loud squawking noise is made in an attempt to startle the predator and make an escape. However, the principal function of the tymbal is to produce calls that assist in attracting a mate and winning her affection. Since some emergences of periodical cicadas can include as many as four different species at the same time, one type of call attracts both males and females of the same species to a common assembly place, such as a large tree. When guys and gals get eye to eye, the male will use a series of distinct and different courtship songs to try and convince the gal that she should be the mother of his nymphs. If the lady likes his advances, she will signal her approval by flicking her wings, often with an audible click.
By vibrating the tymbal, the male cicada produces squawk and courtship calls. Of course the cicada was released unharmed.
After coupling for an hour or more, the male cicada inserts a copulatory plug into his mate, thereby curtailing further inseminations by other suitors. In a deal that seems patently unfair, it is believed that the male cicada then moves on and mates with other females. In the next episode of Bug of the Week, we will explore another chapter in the life of what may be the most fascinating member of the insect world, the periodical cicada. “
Amidst the din of the cicada chorus, the clamor of passing traffic, and even intrusion by a bug geek with a camera, cicadas often stay coupled for an hour or more.
To hear calls made by different species of periodical cicadas, please click on the following link:
Thanks to everyone who has participated in the Cicada Citizen Science project to date. With cicadas up and out of the ground and the Big Boy Band singing their hearts out in the treetops, more than ever we need to know if you have seen or heard cicadas. Please report your sightings at the link below.
CALL TO CITIZEN SCIENTISTS: we need your help! If you see periodical cicada nymphs, shed skins, adults on vegetation or on trees, and hear cicadas chorusing in the treetops, please report your sightings to magicicada.org. Cicada experts are attempting to map the distribution of these magnificent and magical insects. Thank you for your help.
This episode was inspired by curious journalists interested in learning about periodical cicadas. The wonderful article by K. S. Williams and C. Simon, “The ecology, behavior, and evolution of periodical cicadas”, was used as a resource for this episode.