It is a good thing that Yanma rarely live near humans, for their loud, high-pitched buzz makes them among the most troublesome of pokemon. Designed to disrupt the echolocation systems of the Zubat which Yanma prey upon in the wild, when a swarm passes a human settlement the buzz will breaks windows and shatter eardrums until driven away by an outraged, terrified, and often deaf crowd. A single Yanma is an annoying pest, or at times a beloved companion, but a swarm is a natural disaster. Apart from the military, which uses it to disrupt enemy radar, large concentrations of Yanma are unknown among humans, and strict regulations hamper effective breeding of and research into this fast and colorful pokemon. Indeed, even training a single Yanma is taboo where it is not outright illegal.
And this is an enormous shame, for properly trained Yanma can alter the frequency of their buzz. And when the pitch is controlled and made one suitable for large objects and human ears, a Yanma's beautiful song shines through. Many popular composers have used Yanma recordings in their symphonies for generations, although others refused on the grounds that it made it too easy to win fame.
It is said that there is a colony of Yanma deep in the Great Marsh who were exiled there ages ago after their trainer was executed for collecting such a dangerous pokemon. (Others have considered it a strange mutation, for how could a group of Yanma live so long?) Their mournful song is said to be the most beautiful tune in the world, but those who listen to it seldom manage or desire to return to tell the tale.