Mud-Ball Construction by Sceliphron Mud-Dauber Wasps (Hymenoptera: Sphecidae): A Comparative Ethological Study

摘要

Mud-dauber wasps of the genus Sceliphron build aerial nests using mud collected at humid-soil sources and carried to the nest in the form of spherical mud-balls. We recorded and analyzed a series of video-sequences of 5 (3 native and 2 alien) species of Sceliphron in Italy, in order to compare their mud-ball-building behavior. Four phases were recognized: I) patrolling the ground in search of a suitable place for mud-ball building; II) removing leafs, twigs, or small stones from the chosen area; III) forming the mud-balls; and IV) flying off with the mud-balls. The duration of all these phases were similar among species, with the only exception being phase IV, which was shorter in S. curvatum. In all species, mud was shaped into a ball by the combined action of the legs and mandibles, but important differences also emerged in some details of this behavior. In particular, S. curvatum maintained the longitudinal axis of its body parallel to the ground as it worked the mud, and its antennae rapidly tapped the ball. On the contrary, in the other 4 species, the mud was pulled under the mentum and retained laterally by the 1st pair of legs, while the body axis was maintained almost vertical, and the antennae were not involved in mud shaping. Because S. curvatum belongs to a different subgenus compared to the other 4 species, we suggest that mud-ball-building behavior may potentially represent a useful taxonomic and perhaps phylogenetic character