Answer: Caterpillars and slugs tend to munch on hydrangea leaves. If you're finding the damage and not the culprit, try going out at night with a flashlight and checking the undersides of the leaves. I think you'll find the pests. You can bait for slugs and snails. Caterpillars might be butterflies or they could be moths. I'd tend to leave them alone, just in case.
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