What causes the creatures to become spellbound?

The creatures are "spellbound" by the grasshopper's music.

"Wouldn't this be a perfect time for a little music?" the Ladybug asked. "How about it, Old Grasshopper?"
"With pleasure, dear lady," the Old-Green-Grasshopper answered, bowing from the waist.
"Oh, hooray! He's going to play for us!" they cried, and immediately the whole company sat themselves down in a circle around the Old Green Musician -- and the concert began. From the moment that the first note was struck, the audience became completely spellbound. And as for James, never had he heard such beautiful music as this! In the garden at home on summer evenings, he had listened many times to the sound of grasshoppers chirping in the grass, and he had always liked the noise that they made. But this was a different kind of noise altogether. This was real music -- chords, harmonies, tunes, and all the rest of it.