If you’ve walked around Indiana University (or frankly, any woodsy area in Indiana) recently, you’ve probably seen the 17-year Brood X adult cicadas on sidewalks, long grass, trees, and buildings. If you are reading this post and you’ve been in Bloomington for a while, you may also remember the time this happened 17 years ago. Or, you might be like me, and this invasion has sparked a curiosity of wanting to learn more about cicadas.
So you may be thinking, “Why 17 years?” Well, three species make up the 17-year cicadas in the North American region — Magicicada septendecim, M. cassinii, and M. septendecula — and they emerge every 13-17 years in different parts of the continent. Other cicadas spend less time in the ground, so it really just depends on the species and geographic location. The life cycle of cicadas includes: eggs → nymph → molting → adulthood. They spend anywhere from 2-17 years underground until they climb out of the soil to the nearest vertical surface, where they shed their nymph exoskeletons and emerge as adult cicadas. Female cicadas lay eggs in holes they make in trees, and the trees provide shelter and nutrients for the eggs. New cicadas dig underground, where they find plant roots to feed on, and they will stay underground for 2-17 years in a nymph stage, depending on the species. Cicadas do not hibernate; they are active in the ground until it’s time to come out, shed their skin, and become adults. The adults live for about 6 weeks, which is enough time to take to the trees, find a mate, and lay eggs to start the process all over again.
I’m sure you are wondering why cicadas are so loud. Well, something has to attract the female cicadas! Yes, that’s right: the loud humming that you hear is from the male cicadas, because the females are silent. Watch the YouTube video below to learn more about how males make this sound:
In my opinion, perhaps the most interesting part of cicadas is that no one really knows how they are able to “count” years in the ground. But, there are specific patterns to emerging cicadas, which have allowed us to map when and where different broods will emerge! The 2021 Brood X cicadas are primarily concentrated here in Indiana and parts of Connecticut, which is why when you walk outside, you have likely heard and seen a lot of them.
Because I’m sure many of you have an aversion to bugs in general, you may be wondering why cicadas are even necessary in the grand scheme of life. They are actually quite beneficial to the environment, and they play a few different roles. Female cicadas naturally prune trees when they use a sharp, razor-like part of their body, called an ovipositor, to saw into tree branches and lay their eggs. While this effectively kills tree branches, it actually helps sprout new tree branch growth the year following the cicadas’ emergence. Cicadas also aerate the soil, and once they die, they serve as a nitrogen source for plant growth. As you could imagine, they are also a food source for other organisms. While I’ve mostly discussed the 13- and 17-year cicadas, do not be surprised if you see or hear some every summer. There are annual cicadas, but they are typically less noticeable than the 13- and 17-year cicadas because they are a food source for other organisms and they don’t emerge in large volumes. The large quantities of the 13- and 17-year cicadas allow them to reproduce with ease and without fear of predators. If you don’t like them, don’t worry; they only live as adults for 6 weeks, so they should start dying from late June to mid-July.
If you’d like to read even more about cicadas, click here!
National Wildlife Federation (2021). “Periodical Cicadas.” National Wildlife Federation.
Edited by Chloe Holden and Ben Greulich