The Common Descent Podcast

Listen to Episode 190 on PodBean, YouTube, Spotify, or wherever you listen to your favorite podcasts!

These are among the most famous – and noisiest – insects in the world. This episode, we explore the evolution and fascinating life cycles of Cicadas.

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Bombastic Bugs

Cicadas are among the most famous members of the insect order Hemiptera, the true bugs. Like their relatives, cicadas have piercing mouthparts that they use to feed on plants. Cicadas are notable for their large size (commonly a few centimeters long, with some species as big as 20 centimeters) and their large compound eyes, but they’re especially notorious for their noises. Cicadas use a pair of organs called tymbals to rapidly deform the shape of their body and create an incredibly loud call.

Cicadas are also well-known for their intriguing life cycle. As nymphs, they live most of their life underground, equipped with strong front legs for digging, until they emerge as short-lived flying adults to mate and lay eggs. The most famous of these are periodical cicadas, who emerge as adults in large numbers after extended life spans of several years.

North America is home to cicadas in the genus Magicicada, periodical cicadas with 13- and 17-year life cycles, some of the longest-lived insects on Earth. In 2024, a 13-year brood and a 17-year brood (Broods XIII and XIX) will be emerging at the same time, a coincidence that hasn’t happened in 221 years. It will be a spectacular show.

In the fossil record, early relatives of cicadas (cicadamorphs) are known back to the Permian, and they became quite diverse in the Jurassic Period. Among these are the so-called “giant cicadas” of the extinct family Palaeontinidae, which were robust and hairy (similar to modern hairy cicadas), although it’s currently unclear exactly how closely related to true cicadas they are.

True cicadas (Cicadidae) are known as far back as the Cretaceous Period. Fossils from this time already show digging-adapted legs in nymphs, but tymbal structures in adults are more similar to modern-day silent cicadas, so the famously loud calls of modern cicadas might have evolved later on.

Plenty of research has been dedicated to investigating the evolution of periodical cicadas’ peculiar life cycle. It’s unclear exactly what pressures drove the evolution of such long periods of dormancy – hypotheses include the need to avoid regular predators or the need to wait out harsh climate conditions – or how nymphs know when to emerge – some research suggests nymphs might rely on clues derived from plant roots.

Learn More

The cicadas are coming: An entomologist’s take on a once-in-200-years event
Periodical Cicadas Emerge Every 13 or 17 Years. How Do They Keep Track of Time?

Videos:
Bug Expert Explains Why Cicadas Are So Loud
Brood X zombie cicadas infected by fungus are real
The Unique Urination of Cicadas

Advances in the Evolution and Ecology of 13- and 17-Year Periodical Cicadas (technical, open access)
Predator foolhardiness and morphological evolution in 17-year cicadas (technical, open access)
Mesozoic evolution of cicadas and their origins of vocalization and root feeding (technical, open access)
On the morphology and evolution of cicadomorphan tymbal organs (technical, open access)
Cicada fossils with a review of the named fossilised Cicadidae (technical, open access)

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If you enjoyed this topic and want more like it, check out these related episodes:

• Episode 52 – Sounds of the Past (Fossil Bioacoustics)
• Episode 99 – Evolution of Insects
• Episode 181 – Dragonflies

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