Comparative Morphology of the Stinger in Social Wasps (Hymenoptera: Vespidae).

Abstract

Simple SummaryBoth solitary and social wasps have a fully functional venom apparatus and can deliver painful stings, which they do in self-defense. However, solitary wasps sting in subduing prey, while social wasps do so in defense of the colony. The structure of the stinger is remarkably uniform across the large family that comprises both solitary and social species. The most notable source of variation is in the number and strength of barbs at the tips of the slender sting lancets that penetrate the wound in stinging. These are more numerous and robust in New World social species with very large colonies, so that in stinging human skin they often cannot be withdrawn, leading to sting autotomy, which is fatal to the wasp. This phenomenon is well-known from honey bees.The physical features of the stinger are compared in 51 species of vespid wasps: 4 eumenines and zethines, 2 stenogastrines, 16 independent-founding polistines, 13 swarm-founding New World polistines, and 16 vespines. The overall structure of the stinger is remarkably uniform within the family. Although the wasps show a broad range in body size and social habits, the central part of the venom-delivery apparatus—the sting shaft—varies only to a modest extent in length relative to overall body size. What variation there is shows no apparent correlation with social habits. This is consistent with the hypothesis that stinger size is constrained by the demands of a flight-worthy body. The sting lancets bear distinct, acute barbs in all examined species except in members of the Stenogastrinae. Barbs vary considerably among species in number, their summed lengths, and the relative degree of serration (summed length relative to lancet width). Where they are numerous and strong, it increases the likelihood of the stinger remaining fatally embedded in the skin of a vertebrate adversary (sting autotomy). Although an index that combines the number and strength of barbs is a more natural measure of overall serration, the number of barbs alone is almost as good a predictor of the likelihood of sting autotomy. Across the family as a whole, the tendency to sting autotomy is concentrated in the swarm-founding New World polistines.