Under experimental conditions, the fecundity of Typhlodromus athiasae and T. negevi increased with greater availability of prey (Tetranychus urticae), but declined after reaching a level of 32 prey/day. The number of prey killed per egg produced and the number of prey killed/day during the reproductive period increased with prey availability. The total number of reproductive days increased initially, but levelled off at higher levels of prey density. As the prey density was increased, there was a shift in sex ratio towards an increased proportion of females.