The hydrangea leaf-tier (Exartema ferriferanum) is a small moth that lays its eggs on the branches in either the fall or the spring. Upon hatching, the small green black-headed caterpillars sew two terminal leaves together with silk thread, forming an enclosure in which they feed. They feed for about 10 days before pupation occurs. The moths make their appearance a week later. There is only one generation per year. While the damage does not threaten the plant’s life, it may cause the flower buds to abort.