A cloud of houseflies swarming through your home may not sound like music to your ears, but listen closer. The airborne pests are actually giving you an a capella show—always in the key of F. 

Because they lack vocal cords, insects generally make sounds by rubbing their legs together (e.g. crickets), using a vibrating membrane (e.g. cicadas), or moving their wings. The common housefly flaps its wings about 190 times per second, and the human ear interprets that frequency as a pitch along the F major scale (which includes pitches F, G, A, B♭, C, D, and E). While not every housefly is the same size and flaps at the same speed, the measurements are always proportional, insuring the creatures consistently hit the same notes.

Domestic flies are not the only insect with those buzz skills. Despite the fact that Nikolai Rimsky-Korsakov's famous "Flight of the Bumble Bee" is written in a different key, both bumblebees and honey bees “hum” on the same scale as houseflies, according to The Journal of Social Science. It’s no wonder that Beethoven’sPastoral Symphony,” inspired by his love of the outdoors, is written in the key of F. The F major scale is thought to be one of the most prevailing keys of nature.