Why do we hear the sound produced by the humming bees while the sound of vibrations of pendulum is not heard?

The audible range of sound for human beings extends for human beings extends from about 20 Hz to 20000 Hz, therefore, the sounds of frequencies below 20 Hz (called infrasonic sound or infra sound) are not audible and the sounds having frequencies higher than 20 kHz (called ultrasonic sound or ultrasound) are not audible to human beings.

The frequency of the vibration of the wings of a bee is much higher than the oscillations of a pendulum. Humming bees have the sound of higher frequency and it is in the audible range of sound for human beings.