Spatial distribution (quantified by Taylor's power law) and population densities of three scale insect species (Homoptera: Coccoidea) were investigated. The olive scale,Parlatoria oleae(Colvee), was studied on young and old twigs, and on the spurs of apple trees. The Israeli pine bast scale,Matsucoccus josephiBodenheimer et Harpaz, was studied on the stem, branches, and crown ofPinus halepensisMiller. The effect of fruit phenology on the spatial distribution of the citrus mealybug,Planococcus citri(Risso), was studied on grapefruit trees. The highest density of the olive scale was registered in the spurs, whereas the Israeli pine bast scale was more abundant on the stem. The citrus mealybug was more abundant during October. There was no effect of the host section or phenology on the within-species distribution of the three scales, supporting previous claims that the species level of aggregation is a species constant. The species index of aggregation for the three scale insects was 1.3 for the olive scale, 1.9 for the bast scale, and 1.6 for the citrus mealybug. It is suggested that the observed spatial patterns are the result of the intrinsic behavior of the scales (e.g., thigmotaxis and negative phototaxis during crawlers dispersal), the morphological characteristics of the host-plant tissue, and the differential activity of natural enemies. The relatively low level of aggregation of the olive scale is probably related to the activity of an efficient natural enemy, a factor which is negligible in the other two scale species.