Since the concept of the 'niche' was proposed by Hutchinson almost 50 years ago, many researchers have investigated factors that enable species within 'guilds' (i.e., species that exploit a common resource and are likely to compete with one another) to co-exist and to persist. Here, development, host utilization, and life-history characteristics are compared in two species of solitary secondary hyperparasitoids, Lysibia nana and Gelis agilis, attacking pre-pupae of their primary parasitoid host, Cotesia glomerata. More than 80% of the host cocoons presented to L. nana successfully produced adult hyperparasitoids compared with only about 20% for G. agilis. Adult hyperparasitoid body mass increased with host mass, but there was little difference in the mean overall body mass of either species. However, egg-to-adult development time for L. nana was significantly less than that for G. agilis. When provided with unlimited food (honey solution), G. agilis had a lifespan that was almost twice that of L. nana. However, dissections of the ovaries of adult wasps at death revealed that L. nana usually had accumulated more than 20 mature eggs, whereas G. agilis was effectively sterile. We suggest that several eco-physiological factors, as well as differing degrees of specialization amongst the guild of secondary hyperparasitoids attacking C glomerata cocoons, enable them to successfully co-exist in nature. Pieris brassicae (Pieridae) : Host Cotesia glomerata (Braconidae) : Host, Parasite Gelis agilis (Ichneumonidae) : Parasite Lysibia nana (Ichneumonidae) : Parasite Biometrics; Reproduction; Reproductive productivity; Life cycle and development; Development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Competition Cotesia glomerata; Weight; Pupal development; Hymenopteran parasites; Hyperparasitoid life history & development strategies; lepidopteran secondary host; Gelis agilis & Lysibia nana; Lepidopteran hosts; Pieris brassicae; Hyperparasitism Gelis agilis; Lysibia nana; Egg number; Life cycle and development; Hyperparasitoid life history & development strategies in hymenopteran host; Hymenopteran hosts; Cotesia glomerata; Hyperparasitism; Ecological niche; Interspecific competition Pieris brassicae; Hymenopteran parasites; Cotesia glomerata; Hyperparasitism; Hymenopteran parasite & hyperparasite relationship; hyperparasitoid life history strategies none