Generalist predators play a major role in the biological control of many agricultural pests. Most arthropods that are predators as adults are also predators in their immature stages, and may outnumber adults in the field. However, identification of the immature stages is often not possible, because keys, published descriptions, or distinguishing morphological features are lacking. We use PCR to match eggs, larvae (or nymphs), and pupae with identified adult carabids and spiders. We have amplified species-specific mitochondrial Cytochrome Oxidase I (COI) fragments for two Poecilus (Coleoptera: Carabidae) species and two Hibana (Araneae: Anyphaenidae) species. Furthermore, we are able to correctly identify all immature stages – eggs, larvae, nymphs (for Hibana) and pupae – by comparison of the amplified fragment with that of the adults. The use of COI for species identification is a tenet of the Barcode of Life initiative, an international consortium to provide a molecular identifier for every living species.