Silk structure in the hornet cocoon

Abstract

This study deals with the development of a silk coat around the growing larva of the Oriental hornet (Vespa orientalis). Prior to its metamorphosis into a pupa, the larva secretes a silk weave, which enwraps it completely. This silk coat is not uniform throughout, but rather varies along the extent of the larval body. First, it is possible to discern in the spun silk weave fibers whose thickness is approximately 10 microm; in which case such a fiber is actually a duplet of two individual fibers, each with its own silk coat and an inner fibril (core). Additionally, there are silk plaque-like surfaces of a greater diameter and of variable shape, depending on the contour that they cover. In the cap region, i.e. the region where the head of the larva (and later of the developing imago) is located, the fibers are quite numerous and arranged in many (up to 10) layers, while the silk plaques are small. For the remainder of its body, the pupating larva produces a silk sleeve in which there are few fibers with numerous plaques in between, occupying most of the area. The larval silk fibers proper are of fairly uniform diameter. Apart from the pupating larvae, the adult hornets also secrete a type of silk, which acts as a glue holding together the components of the larval cell wall and their sticky silk is of variable thickness, depending on the configuration of the cell. The temperature of the silk varies in accordance with age of the pupating larva. Thus, the closer the developing hornet to eclosion, the lower the temperature. The present study reviews and summarizes this transformation process in the silk weave from its inception until eclosion of the imago.