Pupal Escape Mechanism of Certain Saturniid Moths

Abstract

While photographing the life cycle of the luna moth Actias luna, I observed that the cocoon was being ripped or cut open from withln by a pair of sharp instruments working in opposition to one another. Owing to the thin paperlike construction of the luna cocoon, the escape mechanism was easily observed but not very easily photographed. I observed two black spurs, located approximately 3/8 inch apart, digging into the threads of the cocoon from the inside. They worked in opposition to one another, thus tearing portions of the cocoon threads. Periods of extreme activity were followed by a rest period. At the end of a rest period, the pupa rotated within the cocoon bringing the barbs to bear on a slightly different area at the head end of the cocoon. Eventually a circular opening was torn through the end of the cocoon and the adult emerged. Close inspection of several adults revealed a single spur at the base of each fore wing. These spurs are pointed outward away from each other, toward the apical area of each wing. They are not normally visible on the adult unless the hair-like covering is completely removed. It seems strange that the powerful manipulation of these spurs does not completely wear away the hair-like covering of the upper thorax and basal area of the wing. However, such is the case only on those occasional specimens which have an extremely difficult time freeing themselves. Efforts to find written reference to this device were nearly fruitless. In the words of Dr. Frederick H. Rindge, American Museum of Natural History (personal communication), "The pupal escape mechanism in the Saturniidae has been known for so long that the original references to it are long buried". A. B. Klots (195-) makes brief reference to such devices (e.g., Cossidae, Gracillariidae), and specifically mentions the polyphemus moth and its pair of sharp cutters located at the base of each wing. F. C. Kafatos and C. M. Williams (1964) describe enzymatic fluids secreted by moths to soften the anterior end of the cocoon. The polyphemus moth is among those discussed. Although observations were initiated on Actias luna, later observations were made on Telea polyphemus owing to the lack of mature pupae of the luna moth. Nevertheless, the best observations can be made on Actias luna due to the paperlike construction of the cocoon and lack of thread softening fluid such as is used to assist Telea polyphemus. Inspection of the polyphemus moth revealed the presence of the same spurs on the wings as in Actias luna; in fact, they were considerably larger and more prominent. Several observations were made with Telea polyphemus, to further study the action of the barbs and the associated escape procedure.