The Xyelidae are a comparatively species-poor family of sawflies comprising about 80 extant species in five genera worldwide and is the only family in the superfamily Xyeloidea. The fossil record of the family is extensive, comprising more than 120 species and including the oldest fossil Hymenoptera species dating back to the Triassic, between 245 and 208 million years ago. Xyelidae are to be regarded as living fossils since they represent one of the oldest lineages of insects and include still extant forms. The extant species occur in the Northern Hemisphere, especially in boreal regions of the Holarctic, though there are a few Oriental species. Two genera and about 15 species occur in Europe. Considering additional fossil records from Australia, South Africa and Argentina, the extant species display a relict distribution. The species in the subfamily Xyelinae are associated with conifers (esp. Pinus and Abies), where the larvae feed on pollen or within buds. The larvae of the subfamily Macroxyelinae feed on the leaves of deciduous trees (various Juglandaceae and Ulmus). The family is characterized by the appendages of the head, which are remarkable in that the antennae and palpi are nearly leg-like in structure, with a long basal segment followed by a series of tiny segments, as in the tibia-tarsus. Description Imago (Adult) Xyelidae are small Hymenoptera. Most species are 3 to 5 mm long, but species of Macroxyela and Megaxyela of East Asia and North America are larger, measuring 10 to 15 mm. The imagines display a number of ancestral characters of Hymenoptera, which may be absent in more derived lineages of Hymenoptera. Those include the absence of a wasp waist (thorax and abdomen abut without constriction), presence of cenchri on the metathorax to fix the wings at rest, presence of an antennal grooming apparatus on tibia and first tarsomere of the fore leg, and presence of a molar tooth on the mandible. Most intriguing is the morphology of the antenna which bears a long and thick third article followed by a number of shorter and more slender antennomeres. This so-called synantennomere 3 is the product from the ontogenetic fusion of several antennal articles, and it is unique among the extant Hymenoptera species. In Pleroneura, Xyelecia and most species of Xyela the maxillary palps are strongly enlarged and bear specialized setae on the distal articles. The wing venation is the most complete among Hymenoptera: Only in Xyelidae the radial