What’s eating my hydrangea leaves?!

Hi,

On Monday my hydrangea leaves were pristine. Today - five days later- over half the leaves have holes in them. Mainly in the middle of the leaves but some at the edges. Looked under the leaves and couldn’t see any bugs. This hydrangea has been in the garden for 20 years and has never had anything like this before. Advice and suggestions gratefully received. Pictures attached. Thank you

 

Climate... Caterpillars, wood lice or snail... I would guess the first - do you have oak trees near you?

 

Yes there are huge old oak trees in neighbouring gardens. Is there a pest associated with oak trees?

 

Oak caterpillar, and it is very active at the moment, hence a lot of birds nesting. They drop down from the oak on a thin web and can be blown quite some distance. They obviously like to land on something nice and green and edible... Possible?

 

Ah, I wonder if it is oak caterpillar defoliating my flowering cherry. The canopies of the two touch. It is the first yr I've had a problem.