Abstract Parallel or convergent evolution may result in phenotypically closely similar species. Many studies have reported that using solely traditional external morphological features can result in misidentification. Here, we discuss using the reproductive systems and immature developmental stages for scientific classification in Eupelmidae (Hymenoptera: Chalcidoidea), exemplifying with Anastatus Motschulsky and Mesocomys Cameron (Eupelmidae, Eupelminae). Results show that there are at least 6 distinct differences in the immature stages and the reproductive systems of the adults between species of the 2 genera: (1) the terminal ends of the left and right ovarioles are connected together in the studied species of Anastatus but not in Mesocomys, (2) the base of the lateral oviduct of Anastatus has a diverticulum that is lobate-shaped, whereas this diverticulum is spherical in Mesocomys, (3) the peduncle of the egg of Anastatus is significantly longer than that of Mesocomys, (4) the head capsule of the terminal instar larvae of Anastatus is uniformly translucent, whereas in Mesocomys it has a brown pattern, (5) the ocelli of the Anastatus pupa are smooth and slightly raised whereas the ocelli of Mesocomys each have a long filament each, and (6) the phallobase of adult male Anastatus is sharp basally but rounded in Mesocomys. Our findings not only provide novel insights for the differentiation of similar genera that can be difficult to distinguish in the immature stages but also provide a more comprehensive theoretical basis for clarifying the evolutionary and phylogenic status of Anastatus and Mesocomys.