Cicadas were a species of creature that spent seventeen years maturing underground before reaching adulthood. Once adults, they would live above ground for a period of two months before dying. This gave them enough time to mate and lay eggs before they died. When Licinia Postuma expressed to the Thirteenth Doctor that the life cycle of the Tenctrama seemed odd for any sort of living thing, the Doctor cited cicadas as an example of something similar. Licinia considered the cicada's life cycle strange also, but Ryan Sinclair felt it could make it difficult for predators to find them. (PROSE: Combat Magicks)
According to legend, Tithonus eventually shrunk into a cicada after, per a request to Zeus by a Greek goddess, he was made immortal but not eternally youthful. (TV: Rendition)
Behind the scenes 
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In the real world, a cicada is a tiny insect.
