In last week’s episode, we watched periodical cicadas emerge from the ground after seventeen years, make a mad dash for a tree or other vertical structure, latch on, and shed their juvenile exoskeleton. Many fell to predators or simply failed to escape from their youthful skin and perished without enjoying a moment in the sun. But for the lucky ones surviving the first night of terror, the ghost-like newly molted cicada soon morphed into the spectacular, fully formed cicada bedecked with dazzling vermillion eyes, jet black body, and striking orange wing veins. With haste, survivors made their way to the relative safety of the treetops to complete their transformation into adults. Newly molted cicadas, termed teneral adults, spend the next several days waiting for their exoskeleton to harden before appendages used to insert eggs into branches, or other structures used in flight, sound production, and mating, become fully functional. As this maturation proceeds, cicadas move by foot or wing to treetops and underlying shrubs, vegetation or human-made structures to begin the mating game.
Acoustic signaling, the production of various sounds, is a key element in cicada reproduction. Just behind the thorax on either side on the male cicada’s body, hidden by the wings, is a drumhead-like structure called the tymbal organ. Powerful underlying muscles vibrate the tymbals, creating sound which is further amplified by hollow reverberation chambers within the abdomen of the cicada. While only the male sings, both males and females listen with an ear-like tympanum on the undersurface of their abdomen. Male cicadas have a profound repertoire of sounds. When under attack by a predator, a screechy alarm call issues forth from the cicada’s abdomen. An encounter with the alarm call likely disorients naïve would-be predators or bug geeks handling a cicada for the first time. Creating sound to escape predators is one thing, but the primary function of tymbals and their songs is to ensure the fidelity and perpetuation of the three species of periodical cicadas emerging as Brood X. To successfully reproduce, members of the same species must be in the same place at the same time to find a mate. Using unique and distinctive choruses, male cicadas sing loud and long to attract females and other males of their species to specific locations for the purpose of mate selection. The loudness of the big boy band of hundreds of cicadas singing in concert can range from 80 to more than 100 decibels. These choruses are often in fairly well defined locations such as a single large tree or group of trees. Near my home in Columbia, Maryland, a veteran ash tree has served as the party site for a raucous band of M. cassini for more than a week. Another nearby silver maple trees hosts a mellow chorus of M. septendecim.
A periodical cicada ascends to the treetop to join his brood-mates. Males create sound by vibrating tymbal organs on both sides of their abdomen just beneath their wings. Hundreds of males form load choruses to attract others of their own species. Watch as a pharaoh cicada cruises the chorus using his courtship song to locate an interested female. Nearby, another hopeful male gets the attention of a coy female who flicks her wings several times. Wing flicks accompanied by clicking sounds usually signify a willingness to mate. However, as the suitor closes in to seal the deal, his hopes are dashed when the lady changes her mind and flies away. On a nearby branch another male finds a mate and fulfills his biological imperative.
Once the gals show up to the chorus, it’s all about romance. When cicadas get eyeball to eyeball, the male cicada uses a variety of courtship songs to convince that special someone that she should be the mother of his nymphs. If his performance is good, she will communicate her willingness to mate with choreographed flicks of her wings accompanied by an audible click. Amidst the cacophonous rock concert in the treetops, these teen lovers consummate their interlude with a prolonged bout of mating. Males and females often remain joined for hours during these encounters. Do periodical cicadas really mime Woodstock 1969 every seventeen years? My busy suburban neighborhood lies in the flight path of a major international airport and on warm sunny days lawn mowers and other machines with small engines create a noisome serenade. It has been observed by several folks that cicadas will amp up the volume of their choruses as airplanes soar overhead or lawn mowers create their rackets nearby. A distinguished colleague recently offered that female cicadas likely choose a worthy mate by the loudness of his performance. Apparently, in a strategic competition to find a mate, boisterous, chorusing males are not to be outdone by the noisy contrivances of humans.
Mating cicadas may remain joined for hours. However, when the paparazzi show up and shatter the romance, this shy couple tries to escape the probing lens of the camera.
Bug of the Week thanks Dr. Shrewsbury for helping wrangle cicadas for photography and videography.We thank many members of print and non-print media for providing the inspiration for this episode.
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