According to the hymenopteran pedigree, gynes have a higher coefficient of relatedness with their sons (1/2) than with brothers (1/4). When suddenly confronted with brothers at birth, such females, which can presumably often lay unfertilized eggs, may show fratricidal behaviour in order to grow their own sons. Such a behaviour is assumed to be rewarding if (i) the gynes remain in nest for a sufficiently long time, and (ii) the production of sexuals is continuous during the same period of time. One such case of fratricidal behaviour is described in ants, and, from the literature, at least five cases appear to be known among bees and one possible case among wasps. Many known cases of social insect colonies producing unisexual brood can be interpreted as a mechanism to avoid possible manifestations of such energy-consuming fratricide.