Foliage on hydrangea is being eaten

Question from Shoot User

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Foliage on hydrangea is being eaten very fast. Leaves up to the rod. Can't see anything on the leaf except smth like a fluff and once a dark blue insect. Used Ultimate Bug Killer but to no avail. Plan is in the shade. The same damage but to a much smaller extend is on the rose that is on the sun. What might it be? And how to cure?
Many thanks