Digger wasp predatory behavior (Hymenoptera, Sphecidae): fly hunting and capture by Oxybelus uniglumis (Crabroninae: Oxybelini); a case of extremely concentrated stinging pattern and prey nervous system
Several Orthoptera-hunting wasps usually deliver four paralyzing stings to their prey (one for each thoracic segment and one for the ventral side of the neck) in a predictable, although not immutable, order. This also matches the number of thoracic ganglia of the ventral nerve cord and leg pairs plus the subesophageal ganglion that controls the potentially dangerous mandibles. Oxybelus wasps usually deliver only one thoracic sting, behind one foreleg base, and no neck sting. Many flies have only a single mass of fused ganglia in the thorax, no subesophageal ganglion, and no potentially dangerous mouthparts. Furthermore, some Oxybelus wasps use the sting for prey carriage. The number of thoracic stings matches the number of thoracic ganglionic masses (one), rather than the number of leg pairs (three), thoracic segments (three), or pairs of easily punctured soft membranes (three). This case of extremely reduced paralyzing sequence and prey nervous system is discussed from an evolutionary standpoint and compared with cases in which less or no such reduction occurred. Correlative differences in the state of the prey are also considered.