Leaf tiers on oak

A number of caterpillars use their silk glands to tie two or more leaves together so that it looks like a sandwich. These insects usually do not seriously damage their hosts, and some species can be found on several different trees. Three species of flat leaf tiers that had increased to noticeable levels on red and white oaks in central Minnesota this summer were Psilocorsis reflexella, P. quercicella, and P. cryptolechiella. Reflexella caterpillars have black heads, reddish-brown thoracic shields edged in black, and pale green to yellowish bodies with dark anal shields. Quercicella caterpillars have brownish heads and pale green bodies. Cryptolechiella caterpillars have reddish brown heads and pale pinkish-orange bodies. These caterpillars feed singly between two or more tied leaves, one flat on top of the other, skeletonizing leaf blade tissues except the exposed epidermises which remain as brown coverings. When full grown, about inch long, they drop to the ground, crawl under leaves, change to pupae and overwinter. Small moths emerge the following June, and females lay single egg on the underside of leaves.