The cicadas in the western U.S. aren’t the periodic cicadas that emerge by the jillions on the east coast. But they do live underground as larvae, leave behind spectral pupal casings, and make buzzing and clicking calls with a unique and fascinating organ—more on that later.
This cicada from Mount Pisgah is likely Okanagana oregona. The genus is named after the Okanagan Valley and people in southern British Columbia, and there are about 57 Okanagana species.
A 2017 paper found that these cicadas have an average lifecycle of two to five years. Because some cicadas emerge every year, there’s not a pattern of large broods followed by years of little to no Okanaganas. Interestingly, they emerge in the year when a cumulative rainfall threshold has been reached since they pupated. Which makes me wonder: How do they measure rainfall across multiple seasons? What advantage does this behavior give them?
Using specialized structures called tymbals, Okanagana oregona males make a high-pitched buzz to attract a mate. Females make a clicking sound when they are receptive. Tymbals are on the sides of the abdomen, and they’re composed of a series of tiny ribs, each thinner than a human hair, connected by a membrane. The cicada contracts and expands the tymbal between 300 and 400 times per second to make a buzz.
But here’s the crux move: The tymbal on the left and the tymbal on the right operate independently, and by overlapping the sounds in just the right way, cicadas can amplify their call to astounding levels. In fact, some of the eastern species can make sounds exceeding 100 decibels, equivalent to a power mower or a blender. The U.S. Navy was interested to learn the mechanism, because the agency wanted to use low power to send sounds across long distances underwater.
I found the cicada exoskeleton on the Jette Trail at the David Douglas marker. You can check if it’s still there! It was on the right-hand side of the monument.
Stay curious!
See more of Karen’s work here.
Sources:
Science magazine article on tymbal research: https://www.science.org/content/article/secret-cicadas-chirp. Accessed 7/5/23.
A page on some cicadas that live in Oregon: https://wildcolumbia.org/wildlife-guide/insects-of-northwest-oregon/cicadas/. Accessed 7/5/23.
Research on western cicadas as living rain gauges: https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecy.1980. Accessed 7/5/23.
