or completely absent. The mandibles are well developed and strongly sclerotized. Palps of maxilla and labium lack. The surface of the body is subdivided into distinct segments, each bearing a transverse row of 8−10 backward pointing spines. Biology and behavior Orussid wasps have been collected only rarely. Over the years, their abundance has been subject to strong fluctuations. The species are thermophilous and wasps are active during the hottest hours of the day. Therefore, they are rarely found by the entomologists specialized in sawflies. Only for few species the larval biology is known. Orussidae are parasitoids of xylobiontic larvae of beetles or Hymenoptera, particularly of the larvae of jewel beetles (Buprestidae), long-horned beetles (Cerambycidae), and wood wasps (Siricidae, Xiphydriidae). Orussids can be observed running around quickly on dead tree trunks. The females locate the host larvae living concealed inside wood by generating vibrations by tapping the tips of their antennae against the wood surface. The vibrations are picked up by the modified fore legs. After locating the host, the female drills into the wood with the very long ovipositor and lays the egg. The egg is very elongate with a small expansion on the anterior end and a long expansion on the posterior end. The egg is coiled on the host. In some species the egg is possibly laid into the tunnel of the host if the host itself can not be reached, and the orussid larva itself crawls to the host. On its way to the host it may gnaw through the wood shavings left by the host. It has been disputed whether this material contributes to the nutrition of the larva. At least in Guiglia schauinslandi, the larva lives externally for its first two instars and then enters the putrid(?) liquid in the dead host, where it remains until the adult emerges. Systematics Numerous morphological and genetic studies indicate that the Orussidae form the sister taxon of the Apocrita, the wasps, bees, and ants. Accordingly, parasitic life style has not evolved first in Apocrita but in the common ancestor of Orussidae + Apocrita. Earlier, the Orussidae were sometimes put into a separate suborder, Idiogastra, but today they are classified in their own superfamily, Orussoidea. Orussidae are demonstrably monophyletic. Tribes and subfamilies within the Orussidae have been abandoned, since such earlier subdivisions could not be corroborated in phylogenetic analyses. The cladogram is based on Schulmeister 2003. The Orussoidea are