(With 7 Figures in the Text) The searching behaviour of insect predators has received little attention, with two notable exceptions. Fleschner (1950) compared the searching capacity of the last instar larvae of three predators of the citrus red mite, Paratetranychus citri (McGregor), one of the predators being the coccinellid beetle Stethorus picipes Casey. Banks (1954, 1957) studied the behaviour of first-instar larvae of Propylea quatuordecimpunctata (L.), and of the first and fourth-instar larvae of Adalia bipunctata (L.) and Coccinella septempunctata L. The aim of the present laboratory study of the predatory coccinellid beetle Adalia decempunctata (L.) has been to investigate the mortality which occurs before dispersal from the egg batches, to estimate the effect of topography and feeding on the searching behaviour of the larvae, and to examine the searching capacity of individuals of different instars and their survival, and finally, the effect of prey population density on the rate of increase of the coccinellid. The coccinellid beetle A. decempunctata (L.) and the nettle aphid Microlophium evansi (Theob.), which was used for feeding the beetles, were reared as described previously by Dixon (1958). Until they hatched, egg batches of Adalia decempunctata were each isolated in celluloid pill boxes provided with moist filter paper to maintain a relatively high humidity. These, and the vials in which larvae and adults were reared, were kept in an incubator maintained at 210 C and 66 % R.H. during the day. Fluorescent lighting mounted above a window in the roof of the incubator gave a light intensity of 1398 metre-candles for 16 h a day at shelf level where eggs, larvae and adults were placed. This photoperiod was chosen as it gave best results in rearing the nettle aphid. As few animals thrive well in constant conditions both heating and lighting were turned off at night. PREDISPERSAL BEHAVIOUR IN ADALIA DECEMPUNCTATA Where a predatory insect lays its eggs in batches it is expected that if cannibalism occurs, it must either have some adaptive significance or occur to a limited extent only. The first part of the paper considers the effect of cannibalism on predispersal mortality in Adalia decempunctata, a batch-laying species. In the field, egg batches of A. decempunctata contain from three to thirty eggs (average, fourteen) and larvae may hatch successively over a period of several hours. For about an hour, while the cuticle hardens and darkens, a newly emerged