Schistosomiasis are infectious diseases causing by helminth parasites from Schistosoma genus. The majority of helminth parasites are hermaphrodites except the schistomatidae family which is gonochoric. Moreover, they present a peculiar mating system in animal kingdom: they are monogamous. This monogamy is social but not genetic; in other words schistosomes are not faithful. If the origin of the gonochorism of this parasite seems to be elucidated (i.e. concomitant with the invasion of the warm blooded hosts), the adaptive significance of the monogamy remains to debate. The first part of the presentation proposes hypotheses on the adaptive significance of the schistosomes monogamy according to the classical arguments invoked for free living animals. The second part of the presentation concerns experimental results on various factors affecting the divorce rate. The main results are that female schistosomes are more prone to change of sexual partner than males do and they divorce for genetically dissimilar males