The social spider mite, Stigmaeopsis longus (Saito), builds web-nests and shares resources with fellow nest members. It does not show any distinct morphological castes. In this study, we observed whether there is any division of labor in reproductive and non-reproductive tasks. Under experimental conditions, female density per nest did not affect per capita fecundity, even though the nest area allocated to an individual female, in which it feeds and oviposits, decreased with increased female density. Video observations on the behavior of either one or two females showed that there were no differences between these situations in the time budgets of all behaviors, nor in the nest-weaving behavior of females. Furthermore, detailed behavioral analyses between the two situations suggested that S. longus females share reproduction and labor evenly with their nest mates, probably mediated through physical or chemical communication. Therefore, we concluded that the sociality of this mite species should be categorized as communal.