Observations and reflections from an urban naturalist. #urbannaturalist
The Late Summer Buzz of the Neighborhood: Scissor-grinder Cicada
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"BzzzzzzzzZZZZZZZZZZzzzzzzzzzzzzz!!!!!" As if late summer in Chicago isn't already noisy enough, with late night street festivals, the screech of school buses stopping to pick up children for their first day of school, the thumping sounds of college students moving back in, and all of the other late-season cacophony, you can now add in the nearly constant buzzing call of the Scissor-Grinder Cicada(Neotibicen pruinosis pruinosis) (see figures 1 and 2) to the summer's concluding jam.
Figure 1: Front view of a cicada
Figure 2: Dorsal (top) view of a cicada
You rarely see these noisy creatures, as most of them are high up in the trees. But when one pops down onto the ground, like the one shown in figures 1 and 2, their formidable appearance can be quite a surprise! Do not be alarmed, however, as cicadas are harmless to people.
Figure 3: Location of tymbals on a cicada.
Cicadas actually spend most of their life underground as larvae, feeding on the juices from the roots of trees. Their feeding activities seldom harm the tree, and there are probably billions of cicada larvae living beneath our feet, even within urban areas like Chicago. After about two or more years, the larvae will emerge from beneath the ground, climb into the trees, and will molt, or shed their larval exoskeleton. Their adult life is brief, lasting only a few months as they call and look for mates.
Their call for mates is extremely loud, and that's because cicadas have sound-producing organs in their abdomens, known as tymbals, which rub rapidly against their ribbed abdomen (figure 3). Here's a video clip of a cicada's tymbals in action:
The molted skins and the dead adults serve as an important food source for many species of wildlife, including birds and mammals. Cicadas require areas with mature trees in order to meet their life needs. The most commonly encountered species in the University Village neighborhood of Chicago is the Scissor-grinder Cicada, but you might also hear the very closely related Linne's Cicada (N. linnei) in larger greenspaces. A third species of cicada is present in the Chicago region, but you won't hear or see them in their adult form until the late spring of 2024 in natural areas along the outskirts of the Chicago metro area. This is the notorious Periodical Cicada, and adults emerge only once every 17 years in massive numbers. The reasons behind why periodic cicadas wait this long to emerge is not well understood, but it has been a phenomenon happening in our region since long before the first skyscraper was built. You can view an excerpt from BBC to learn more about Periodic Cicadas:
Once cooler weather sets in, the vibrant calls of cicadas will cease, and only the larva that live underground will survive the winter. So as the last days of summer roll in, enjoy the final song of one of our most ubiquitous singing insects, the annual cicadas.
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