We investigated the value of microsatellite DNA markers to improve our knowledge of mating strategy with inference to sperm competition in particular, in the woodlouse Armadillidium vulgare. In terrestrial isopods, mature females develop a brood pouch or marsupium before egg laying, the pouch being formed by overlapping oöstegites during a special moult called parturial moult. Under laboratory conditions, we show that Armadillidium vulgare females are able to mate during parturial intermoults, even in the presence of a physical barrier such as that represented by the ventral marsupial plates. Our results reveal that the contribution of a second male mating with a female between two parturial moults could represent up to 50% of the paternal alleles in the brood (mean¼28% 6 15). This contrasts with data reported in the literature concerning closely related woodlice species, where males are suggested not to be able to mate with the female during the parturial intermoult period.