Since the early 1900s, the Eurasian woodwasp (Sirex noctilio F.; Hymenoptera: Siricidae), a pest of pine (Pinus spp.; Pinales: Pinaceae) trees, has been introduced to various regions in Southern Hemisphere and North America. Among the most effective biocontrol agents of S. noctilio are hymenopteran parasitoids that parasitize various life-stages of woodwasps. Little is known about how these parasitoids locate their host in the wood, but presumably do so through chemolocation using antennae. We examined the external antennal morphology of Ibalia leucospoides ensiger (Norton) (Hymenoptera: Ibaliidae), a major parasitoid of native siricids in North America. Males were found to have two more antennal flagellomeres (13) than females (11), although the total antennal length was similar. The first flagellomere of the male has a distinctive excavated region. Using scanning electron microscopy, we identified seven types of antennal sensilla on male and female I. l. ensiger including campaniform, chaetica (types 1 and 3), coeloconic, fluted basiconica (FB), pits (PI), and placodea. There were no differences in the total number of antennal sensilla between male or female I. l. ensiger. However, females had greater numbers of chaetica type 1 and FB, whereas males had more sensilla placodea. Sensilla were unevenly distributed along the antennae of both males and females. Chaetica type 1 was the most numerous sensillum followed by FB, placodea, and PI. We present analyses of the morphology of the antennae of each sex of I. l. ensiger, and discuss possible function of each sensilla-type and how they may mediate mate location and oviposition activities.