|Those silk stitches are a characteristic feature of both leaf rollers and leaftiers (mentioned below).|
|Looking inside the leaf, you can see residue of a silk nest. There are also tiny black orbs which are possibly leftover eggs.|
Because this plant is a hydrangea, I briefly thought that it was a Leaftier at work. There is one species that prefers hydrangeas in particular. But the leaf webbing habits of this creature seem more consistent with those of leaf rollers. Here is a concise description of the differences between the habits of leaftiers and leaf rollers (in this case with respect to oak trees, but relevant to all trees and plants they use):
"The leaftier larva (caterpillar) binds two or more leaves together with strands of silk and then feeds and rests between them. The larva is found by separating the tied leaves (cover photo). After feeding ceases, the larva drops to the ground and pupates in the litter or duff. The leaftiers of oak include a small group of tortricid moths and three other minor families.
"The leafroller larva rolls or folds one leaf, then binds it with strands of silk. It feeds and rests within the rolled or folded leaf (Figure 2). The larva is found by unrolling the partially folded leaf. Although some larvae may pupate in folded leaves, most pupate on the ground. The leafrollers of oak are comprised of more than 15 species of moths in 5 families. Of these, about 60 percent are tortricid moths."
If anyone has any information, it would be greatly appreciated. Fortunately it appears that no real harm has come to the hydrangea (the work of leaftiers and leaf rollers can be very destructive).
As a side story, I discovered that, while the larvae seem to have abandoned these rolled-up leaves, a slug found one of them a convenient and cozy daytime hideaway!