Hydrangea leaves that look like this contain a grub, a stage of the leaf curl moth. The moths lay their eggs on the leaf then spin a fine silk like web around the eggs to attach them to the leaf. The silk threads cause the leaf to curl protecting the eggs from predators like birds. The eggs hatch into caterpillars that eat the leaf and soon become adult moths, continuing the cycle.
Moths prefer leaves of lilac trees due to their softer texture, but if a hydrangea is next to a lilac, the moths will lay their eggs on hydrangea leaves too. As soon as you see the leaves curled on either lilac or hydrangea bushes or trees, remove the leaves and burn, crush or shred them to kill the eggs.
I saw some of these on hydrangea leaves last summer. I tried to kill the worms and eggs by spraying with tea tree oil, but it did not seem to work. I then cut off the infected leaves, which seemed to help.
We are starting a veggie patch today and came across a cabbage moth grub…those green ones. Also found a few aged dog bones and my daughter set up a museum to display their finds. Gardening is so much better for them, obviously, that a day on Minecraft. My husband has been out there with them while I sort through crates transitioning from Summer to Winter. Making good progress but you’ve reminded me that I also need to take a bit of time out to enjoy the gardening xx Rowena