Using incorporated devices, Tetranychus urticae spider mites were rinsed from hydroponically-grown lima bean plants, collected, separated and blow-dried. This yielded a reliable and large volume of eggs and larvae, which were fed to Amblyseius womersleyi rearings on 15 x 5 cm2 polyethylene arenas. Of several feeding regimes tested, daily feeding of 10 mg T. urticae eggs and larvae resulted in the highest predator population levels. The best harvest period was between 15 and 27 days, when predator density exceeded 600 mites per arena. A preliminary automatic mass-rearing device was tested for A. womerslyi. This incorporated both rearing and harvesting procedures. A micro-feeder was developed to supply the required volume of spider mites and maize pollen (1:1 mixture) to the predators. A Bakelite rearing arena reduced the space requirements of a polyethylene arena, was more durable and an essential component in the automatic mass-rearing and harvesting. Mite harvesting is carried out through the use of a vacuum-head harvester. Supplements of (sterilized) spider mites, pollen, vermiculite and wheat bran are automatically added to the predators. The devices for harvesting, filling and packing are incorporated and synchronized and the entire system is controlled by a single slide-switch. The design and system can be expanded without changing the basic processes and program, for example to adopt it for other species of predaceous mites.