I play the keyboard for a little country church. After one of the COVID-careful services, I complained to my husband that it felt wrong, somehow, to play hymns when nobody was singing.
He pointed out that, although the congregation wasn't singing, a cricket was.
To be technical, crickets do not sing.
It's more like percussion, a sound made by striking or scraping.
In the case of crickets, the sound is made by scraping, almost exactly the way sound is made when playing the güiro. It's a Latin percussion instrument that's made from a gourd or fish-shaped piece of wood with little serrations. A musician scrapes it with a stick.
A male cricket has a very thick vein on each wing. This vein has somewhere between 50 and 300 microscopic serrations. When the cricket pulls this toothed vein across its wing, it makes a rhythmic sound just like a güiro.
To amplify the sound, a cricket raises his wings to a 45-degree angle. The raised wings and body act as an echo chamber and make the chirps louder.
Or, at least loud enough that the female crickets can hear. Females don't have ears. Instead, they detect the sound with eardrum-like organs that are just below the knees on their front legs.
When the male cricket scrapes the specific rhythm of his species, the female can locate an appropriate mate, even in high grass.
Once the female finds the male, he changes his chirp and produces a courtship song.
He's not singing, though - it's percussion.