Many male insects, including grasshoppers, crickets, cicadas and some beetles, sing to advertise their presence to potential mates. Songs are mostly produced by stridulation - sound production by rubbing two body parts together. One part (the plectrum) is usually membranous and can be made to vibrate, while the other (the stridulitrum) is notched and causes the plectrum to vibrate when scraped against it.
Some of these songs are audible to humans, but many others use frequencies that are too high for us to hear. The Australian bush on warm nights is alive with stridulatory songs, only some of which we can hear.
Of all these singing insects, the common Australian moth Syntonarcha iriastis has one of the most remarkable ways to sing to passing females. Males of these small moths perch at night in the crowns of gum trees right around Australia, and stridulate their genitals. One part of the genital apparatus is dilated and forms the plectrum, while another part is the notched stridulitrum. Males spread their wings, spread their genitals, and sing!
Unfortunately, we can't hear them: they call at 42 and 57 kHz, well above human hearing range. They can, however, be readily detected using a bat detector, which converts ultrasonic frequencies to audible sounds.
Syntonarcha iriastis is common in parks and gardens around Australia. So next time you're strolling at night in Kings Park in Perth or the Domain in Sydney, try to imagine all the tiny moths perched on trees in dark corners of the park, genitals outstretched, stridulating away.
Then again, maybe it's best not to.