Structure and function of the large pronotal horn of the sand‐living anthicid beetleMecynotarsus tenuipes

Abstract

AbstractLarge insect horns function as antipredator armaments, digging implements and intraspecific combat weapons. The sand‐living anthicid beetleMecynotarsus tenuipespossesses a large horn on the pronotum. Allometric relationships between body size and horn size did not show either a slope of more than 1 or sexual dimorphism, suggesting another function of the horn other than sexual selection via combat. Behavioral observation of individuals using a microvideo camera indicated that the horn is used to dig and move forward in loose sand. Only the hornedM. tenuipescould dig into sand, in contrast to the hornless anthicid beetlesStricticollis valgipesandClavicollis fugiens, which could not dig. When moving in sand,M. tenuipesjoins its pronotal horn and head to form a conical shape, with which it pierces into the sand. Then, it opens its horn and head outward to create a space in the sand for forward motion. Although it can dig deeply into sand by repeating these behaviors sequentially, digging speed tends to slow with depth, probably because the weight of the substrate increases.