The family is based on the genus Oryssus, which comprises only a few species. H. E. Burke in 1917 established that O. hopkinsi Roh. and O. occidentalis Cress were parasitic, being solitary internal parasitoids of buprestid beetle larvae (Clausen 1940/1962). Little further is known about the habits of these species, and of the immature forms only the final instar larva and pupa have been described (Parker 1934).
Mature larvae of O. occidentalis (Rohwer & Cushman 1917, Parker 1934) bear a close resemblance to chalcidoid larvae of the same instar. It is subcylindrical, with 13 body segments, the legs indicated by sclerotized disks, and each segment bears a transverse row of 4-5 short, stout spines at each side of the dorsal median line. There are 10 pairs of spiracles, situated on the last two thoracic and the first eight abdominal segments. Those of the metathorax are rudimentary and nonfunctional. The head is small, with tubercle-like antennae, and the mandibles narrow and tridentate. Female pupae bear the ovipositor over the dorsum, extending slightly beyond the head. The second to eighth abdominal tergites bear transverse rows of spines at the sides.