The pitch of the buzzing noise made by bees and wasps depends on the number of wing-beats per second. The smaller the bee or wasp, the higher the number of beats, resulting in a high pitch sound. The larger the bee or wasp, the lower the number of wing-beats, resulting in a low pitch sound. Another factor is the age of the insects; older ones will have some damage to the surface and edges of their wings. This lowers the number of beats per second, and alters the sound pitch.