Ask A Scientist
Why do cicadas make that annoying noise?
Asked by: Eddie Faughnan
School: Seton Catholic at All Saints, Binghamton
Teacher: Eric Saeger
Hobbies/Interests: Lacrosse, basketball and watching TV
Career Interest: Architect
Answer from Debbie Dittrich
Research Support Specialist, Binghamton University
Research area: Teardown analysis of electronic packages
Interests/hobbies: Docent at the Binghamton Zoo, nature photography and gardening
Large and pudgy with bulging eyes, adult cicadas are rather cute insects. Most range in size from .79 to 2 inches, but the largest species is almost 3 inches long with a wingspan of 7–8 inches. You won’t find any that large around here, however as those big guys inhabit Malaysia. In fact, cicadas can be found in every continent except Antarctica. The noise cicadas make is actually a song that the male cicada uses to attract a female. This song is produced by structures called tymbals, which are located on the sides of the male’s body. Contraction of the tymbal muscles pulls the tymbals inward, relaxing the muscles returns the tymbals to their original position, each time producing a clicking sound. The abdomen of the male is largely hollow, amplifying the sound like a drum. Each species produces a different song so that the female can select an appropriate mate. Males can also produce alarm calls. Females lack tymbals but they can make clicking or snapping sounds with their wings.
After mating, the female cuts a groove into a tree branch into which she deposits her eggs. The eggs hatch into nymphs, which resemble white ants. Cicadas eat tree fluids that the mother cicada makes available to the nymphs by creating the groove in the branch. The nymph stays in the groove and feeds for a short time, then falls to the ground and burrows down to the tree roots where again it feeds on tree fluids. From 2–17 years, most of the cicada’s life is spent underground. When the nymph has finally matured, it will come out of the ground and shed its skin one last time. It is now an adult with only a few weeks left to live.
Adults of some species of cicadas appear every year. These are annual cicadas. There are also periodical cicadas, which have life cycles of either 13 or 17 years depending on the species. Periodical cicada adults all appear together after either 13 or 17 years (there are no adults of these cicadas in the years in between). Periodical cicadas are found only in eastern North America and can reach concentrations of tens to hundreds of thousands per acre. The summer of 2013 was the time for emergence of the Brood II 17 year cicadas. If this past summer was particularly noisy in your neighborhood you were lucky enough to have experienced these periodical cicadas.