Urban Buzz: A Periodical Cicada Citizen Science Project

2014 Cicada Brood Map
Periodical cicada (Magicicada spp.) populations are vulnerable to the ways we change the land around us. They live in the dirt. They suck on plant roots. They are born one year and then 17 (or 13) years later rise to often find a landscape quite different from the one their parents experienced. When forests (and with them, tree roots) disappear completely, periodical cicadas never emerge at all, but in many cases forests do not disappear entirely, they just change. With urbanization, they become hotter, more polluted, and, more afflicted by herbivores other than the cicadas. What do these changes do to periodical cicadas? We don’t really know.

For a short-lived organism, urbanization may speed up its life cycle or affect its vulnerability to predators. For long-lived, stationary organisms, these effects might be even more pronounced. In the case of periodical cicadas, it’s likely that chronic exposure to stressors associated with the urban environment may affect cicada development, physical characteristics, and ultimately how many offspring they contribute to the next generation.

One particular aspect of the cicadas that is likely influenced by urbanization is how crooked they are – that is, how much the length, width and shape of parts on the right and left side of the cicada body, respectively, differ from one another. Scientists have given a fancy name to these small, random deviations from perfect symmetry; they call it fluctuating asymmetry (FA).

How does fluctuating symmetry happen? In general, traits on the left and right side of the body should be symmetrical (or mirror images of each other) because they are products of the same genome. But sometimes, something happens during the process of an organism’s development — say it’s exposed to a pollutant or extreme heat – such that this environmental stress disrupts development, resulting in random and subtle ‘abnormalities’ from perfect symmetry.

Fluctuating asymmetry has been used as a low cost way to monitor the effects of environmental stressors like pesticides and water pollution on terrestrial and aquatic insects. We think it might be a quick-and-dirty way to gauge the negative effects of urbanization on periodical cicadas – We predict that cicadas experiencing more intense levels of urbanization (as measured by the amount of forest cover or concrete and blacktop in an area) will be more crooked.

And so we need your help! We are asking all of you living within a periodical cicada emergence zone to collect and send us 5-10 dead periodical cicadas in good condition. We want samples from forests, from cities, from suburbs, from farms – in other words, across a gradient from low to high urbanization.

With the help of high school students, undergrads and possibly some of you, we’ll then measure traits of the cicadas on the left and right sides of their bodies, traits like the presence and length of wing veins, leg segments and the number of ridges on the cicadas’ noise-making organs (called tymbals). We’ll then use these measurements to calculate fluctuating asymmetry and test our urbanization hypothesis.

We encourage you to collect samples from as many distinct geographic locations as possible.

Note: Sampling now complete. Thank you for your participation!