Part of their body is hollow, this amplifies the sound. The longer you listen to their sound, the more they seem to sync up

Of all the languages’ words for cicada, Croatian’s might be the best: cvrčak, pronounced: tvr-chak. The sound it makes is tvr-chi tvr-chi. I have a Croatian friend who taught me part of a poem – Cicada – when we were in high school. It is by Vladimir Nazor, who was Croatia’s first head of state. The first stanza includes the satisfyingly low on vowels and onomatopoeic phrase: “cvrči, cvrči cvrčak” (pronounced “tvrchi, tvrchi tvrchak”) – which translates as “chirp, chirp cicada”.

And the cricket chirps, chirps on the knot of the black spruce
Its deafening trochee, its sonorous, heavy iambic …
It is noon. – Like water, it spills out in silence.
A solar dithyramb.