Posted: 15/04/2016 at 14:37
Aym, worms come to the surface because the vibration mimics rain falling on the ground - they come to the surface because the increased humidity means that they can move around on the surface of the ground without drying out.
Seagulls and some other birds have learnt to mimic the rain by padding up and down with their feet so that worms come to the surface and provide the gulls with lunch. I frequently watch them do this on a cliff-top cricket pitch near my mother's home.
It is nothing to do with the worms being frightened. I think you must've misunderstood - if not, then Chris Packham's reputation for scientific accuracy has fallen in my estimation.