Leaves being eaten by an invisible pest
Please can anyone help me identify what is eating the leaves of so many shrubs and plants: clematis, chaenomeles, roses, robinia, cercidiphyllum and it is rampant on climbing euonymus.
All have large sections, often circular in shape, eaten out of them. There is not always evidence of caterpillars or grubs at work, though occasionally we find leaves wrapped up around a small green caterpillar and a small web.
Occasionally also there are small brown, squarish patches on the reverse of the affected leaf but not always.
Also there may be very small black or grey flat insects which may or may not be scale. But do these eat such large areas of leaf so quickly?
I have found some vine weevils but think this may be a coincidence.
But none of these are present in all cases and much of the damage is done with no evident culprit in sight.
Help please. What is causing such extensive damage so quickly?