Hi

It looks like Hydrangea leaftier, Olethreutes ferriferana

The hydrangea leaftier is a caterpillar that affects smooth hydrangea, H. arborescens. The caterpillars are light green with a dark head and cause damage by tying the leaves at the top of branches together using silk-like threads, creating a pocket-like structure with the leaves (Fig. 1). The caterpillar is well protected in the structure and feeds on the young leaves in the bud (Fig. 2). The damage to the plant is primarily aesthetic and is unlikely to impact the health of the plant, though some damage to flowers can occur.

Hydrangea leaftier is easy to control with minimal effort. The caterpillars can be squished by either opening the tied-leaf structures, locating the caterpillar, and squishing or by thoroughly squishing the pockets. The tied together leaf structures may also be removed and destroyed, though this may affect the quantity of blooms if the flower is also removed. The insect is well protected from insecticides inside the leaf pockets and therefore manual control is the best option. Look for the tied together leaves in May and early June.

Here are some fact sheets that we think will be helpful to you.

https://www.uvm.edu/news/extension/hydrangea-leaftier

https://bygl.osu.edu/node/1979

https://cceschoharie-otsego.org/resources/hydrangea