The Hydrangea Leaftier Moth (Olethreutes ferriferana, family Tortricidae) is so-named because the caterpillars tie together developing leaves on wild and cultivated hydrangeas to produce oddball “leaf-purse” structures. The caterpillars have completed their development in southwest Ohio but their handiwork remains.
Individual caterpillars apply silk along the edges of newly expanding hydrangea leaves to cement or tie the leaves together. This creates a purse or envelope-like structure that surrounds both newly developing leaves and flowers. The tied leaves fail to fully expand and become dark green, wrinkled and gnarled; the structure may superficially resemble a plant gall
The caterpillars feed upon the leaves and flowers enveloped within these protective structures. Opening the tied leaves will reveal the caterpillars housed within silk casings littered with dark green frass pellets. The green semi-transparent caterpillars are very small and have shiny black head capsules and a black thoracic shield on top of the segment just behind the head.
The leaf structures created by this leaf-tier caterpillar tend to occur near the tips of plant stems and may be very obvious. While the structures may look very odd, the damage appears to cause little harm to the overall health of its namesake host despite noticeably reworking normal leaf architecture.
Currently, the caterpillars in southwest Ohio have completed their development. I examined the leaf structures on hydrangea in mass plantings in three locations and found either pupae within the structures or pupal skins hanging out of the structures indicating that the moths are on the wing.
I've never seen the caterpillar damage to wild or cultivated hydrangeas progress beyond the "oddity category." This is important because the leaf structures shield the caterpillars from direct exposure to a topical insecticide and there is no data on the efficacy of systemic insecticides. If caterpillars are active, they can be dispatched through death by squeezing.
Fortunately, the hydrangea leaftier moth only has one generation per season, so no new leaf-nests will appear. Unfortunately, the current leaf structures will remain evident for the rest of the season.
On the other hand, according to the literature, leaf shelters constructed by this and other lepidopterous larvae play an important role in forest ecology by sheltering spiders and other arthropods. I was surprised at the number of earwigs that I found in leaf structures. Given that the earwigs were in various stages of development, I’m speculating that they must have co-existed with the moth caterpillars without killing them.
The same is true for spiders. They commonly seek shelter in the hydrangea leaf abodes created by the leaftier caterpillars. It’s reported they may arrive before the lep-architects vacate the premises; however, they don’t kill their benefactor. Otherwise, spiders are beneficial predators that often target other insect pests.