30 UK species. Length ~2mm, metallic. Occipital margin sharp, frontovertex broad, antenna inserted low on face, level with the bottom of the eyes. Mesotibial spur long and slender, last sternite (hypopygium) triangular and reaching apex of abdomen. The top plate of the thorax (mesoscutum) is completely lacking notauli (the pair of longitudinal parallel grooves common in other parasitic wasp groups).
Female antennae with 6 distinct funicle segments (the segments making up the main antenna shaft) terminating in a 3-segmented club that features a distinct oblique truncation—the very tip looks like it was sliced off at a clean, sharp angle. Males antennae filiform (thread-like), covered in conspicuous whorls of long hairs and the club at the end is  unsegmented.
Forewing postmarginal vein is extremely short - barely longer than it is wide. There is a distinct, broad, hairless diagonal stripe (called the linea calva) slicing across the basal third of the front wing.
Mandibles usually tridentate.

Unless identified by a recognised expert, explain how it was identifed and submit detailed photos.

Parasitoids of Lepidoptera with an unusual process of polyembryonic development from one egg within the host larva. The egg divides into an irregularly branched chain of cells, each of which becomes a separate embryo. The resulting endoparasitic larvae consume the host larva and pupate within its swollen and distorted skin, with the emerging adults being all of one sex, unless more than one egg was deposited initially.

Widespread.

Unknown.