The Leucospidae (sometimes incorrectly spelled Leucospididae) are a specialized group within the Chalcidoidea, composed exclusively of ectoparasitoids of aculeate wasps or bees. They are typically mimics of bees or stinging wasps, often black with yellow, red, or white markings, sometimes metallic, with a robust mesosoma and very strong sculpturing. The hind femora are often greatly enlarged, with a row of teeth or serrations along the lower margin as in Chalcididae. The female ovipositor is sometimes short, but if not, it is recurved and lies along the dorsal side of the metasoma, a unique feature. The males are also unusual, in the fusion of many of the metasomal segments to form a capsule-like "carapace".
A fossil species Leucospis glaesaria has been described from Early Miocene amber from the Dominican Republic.
They are parasitoids of hymenoptera, mostly solitary bees but some solitary wasps, and there is a case of a hyperparasitoid. Leucopsis dorsigera that has been found as a parasitoid of Xorides sp. which in turn was a parasitoid of a cerambycid beetle larva boring inside the stems of apricots. Leucospids are generally rarely encountered except in areas where their hosts are abundant; in the United States, the most common species is Leucospis affinis, which attacks nests of leafcutter bees.
About 130 species are known of which nearly 44 are from the New World, mostly from the Neotropics.