Elachertus scutellatus Howard is a synovigenic, koinobionic ectoparasitoid that preys on the Brazilian skipper caterpillar, Calpodes ethlius (Stoll) (Lepidoptera: Hesperiidae). This wasp exhibits a rare combination of life history strategies, some associated with being a koinobiont and others with being ectoparasitic. The female wasp lays large, inflexible, anhydropic eggs that are passed externally down the ovipositor. This process is uncommon and is considered the morphological intermediate between the use of the ovipositor as an egg-laying device and a stinger. The average clutch size and the oviposition frequency of E. scutellatus females are comparable with other wasps in the Eulophidae. Female wasps were observed to be nonconcurrent host-feeders. The sex ratios of E. scutellatus broods were consistently female biased. Adult male wasps lived longer than female wasps, which may have been a result of host size or the rearing technique used. E. scutellatus has potential as a biocontrol agent because of its female-biased sex ratios, destructive host-feeding, and synovigeny.