Pelidnoptera nigripennis (F.) is a parasitoid of the millipedes Ommatoiulus spp. in Portugal. It is univoltine. The adults lay eggs on their hosts during the spring in southern Portugal, and the first-instar larva penetrates through the soft tissue of the millipede. The parasitoid spends the summer as a firstinstar larva, kills the host during the autumn when in the third instar and overwinters in the pupal stage. P. nigripennis occurs in habitats of low bushes, but not in open grasslands. The female searches for prey by day. The maximum rate of parasitism recorded in this study was 20%. In laboratory specificity studies, 15 species of millipedes from five families were exposed to P. nigripennis, but only julid millipedes were successfully parasitized. Synchronization of the life-cycle in the laboratory with the seasons of the southern hemisphere was achieved by inducing pupation five months prematurely after cooling to 10°C.