The life cycle of two morphologically very similar Diplogasteroides species and their association with cockchafers in southern Germany was investigated. 70-100% of cockchafer grubs and 95% of the imagines carried Diplogasteroides spp. dauer juveniles. The nematodes were almost exclusively found on the external cuticle of the insects and usually not in the body cavity or the intestine. Diplogasteroides spp. dauer juveniles embark on the grub and accumulate during its development. There was some indication that dauer juveniles are transmitted from male to female beetle during copulation. The dauer juveniles resume development only after the death of the beetle, feeding on the cadaver (necromeny). Former hypotheses, assuming the nematode species to be parasitic and to cause the death of cockchafer grubs, can be refuted.