The effect of the different stages of two tetranychid prey species on the predatory efficiency and biology of the stigmaeid mite, Agistemus exsertus Gonzalez was studied. It was found that feeding the predatory immatures on eggs of Tetranychus urticae (Koch) favoured faster development compared to feeding on eggs of T. cucurbitacearum (Sayed) although the eggs of the latter prey were more attractive to the predator. Also rearing the predatory mite on eggs of either tetranychid prey promoted faster development and a higher rate of oviposition than rearing on larvae or nymphs.