Insects share a body plan based on repeating segments. Segmentation has been well characterized in Drosophila melanogaster, in which segments are established by a genetic hierarchy including gap, pair-rule and segment polarity genes. Pair-rule genes (PRGs) are a key class of segmentation genes as they are the first cohort of genes expressed in a periodic pattern. Segments are established simultaneously in Drosophila in early embryos, while most other insects add segments sequentially as the embryo elongates. Our goal is to understand molecular mechanisms controlling segment formation and to determine the extent of their conservation during evolution. Here, we established the hide beetle Dermestes maculatus, an intermediate germ developer, as a new model system for studying segmentation patterning. We first established a lab colony and studied early embryogenesis in Dermestes. All nine PRG orthologs were isolated using degenerate PCR and RACE, and their expression patterns were examined with in situ hybridization. Except for opa, all Dermestes PRG orthologs are expressed in PR-like striped patterns. Gene functions were tested using RNA interference (RNAi). We examined both hatched and unhatched larvae to uncover defects with different severities. Both Dmac-prd and -slp knockdown resulted in typical PR defects, suggesting that they are “core” PR genes. Dmac-eve, -run and -odd have dual roles in germ band elongation and in PR segmentation, as severe knockdown caused anterior-only, asegmental embryos while moderate knockdown resulted in PR-like defects. Elongated but asegmental germ bands resulted from Dmac-prd and -slp double knockdown, suggesting decoupling of germ band elongation and PR segmentation. Extensive cell death prefigured the cuticle patterns after knockdowns, seen long ago for Drosophila PR phenotypes, although disrupted cell mitosis was also observed after Dmac-eve knockdown. We propose that PRGs have retained basic roles in PR segmentation during the transition from short-to-long germ development and share evolutionary conserved functions in promoting cell viability. Finally, I also present detailed protocols on Dermestes lab rearing, embryo collection and fixation, in situ hybridization and RNAi. The technical information described here will provide useful information for other genetic studies in this new model system.