Hydrangea Leaftier Moth (Olethreutes ferriferana, family Tortricidae) caterpillars develop inside oddball “leaf-purse” structures on wild and cultivated hydrangeas. The beautiful native moths are grouped into the non-taxonomic category “microlepidoptera” owing to their small size.
The common name “leaftier” is based on the behavior of the moth caterpillars. Individual caterpillars apply sticky 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 newly developing leaves and flowers.
The leaf abodes most commonly involve two leaves cemented together. However, the caterpillars will occasionally fold a single leaf. The tied leaves fail to fully expand and become dark green, wrinkled, and gnarled. The oddball structures may superficially resemble plant galls.
The caterpillars feed upon the leaves and flowers enveloped within these protective structures. Opening the tied leaves reveals a single caterpillar housed within a silk-lined tube littered with dark green frass pellets. The green semi-transparent caterpillars are very small, with 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.
There is a single generation per year in Ohio. Caterpillars develop rapidly in the spring and pupation usually occurs in southwest Ohio in early to mid-June. However, the purse-like handiwork of the caterpillars remains evident throughout the rest of the season.
Last week, I examined the leaf structures on hydrangea in mass plantings in three locations in the southwest part of the state last week. I found either pupae or pupal skins hanging out of the structures meaning new moths had emerged.
Damage to wild or cultivated hydrangeas seldom progresses 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 or pupae are found within the structures, they can be dispatched through death by squeezing.
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. Indeed, it’s common to find earwigs and spiders sheltering in the hydrangea leaf abodes before the caterpillars vacate the premises. The spiders will co-exist with the caterpillars without killing their benefactor.