A 5 year study of the foliage inhabiting fauna of young apple trees which had never been treated with insecticides or miticides showed there were large numbers of species varying considerably in quantity. The study also showed that the manner in which the foliage is distributed by cluster type and the distribution of the many species on the clusters are important factors in the sampling of mixed populations of arthropods.The leaf clusters were classified into six types based on stem length and on the presence or absence of fruit. The mean number of leaves per cluster for all types combined increased until mid July but no further increase occurred after that. The variation in leaves per cluster on the longer clusters, however, continued throughout the summer even though the mean number of leaves per cluster did not.The relative abundance of each of the arthropod species, whether it was identifiable to name or not, was given a quantitative rating by using random clusters as a common sampling unit. Eleven orders, 38 families, and over 100 species were recorded. The species making up the fauna were nearly all at a low density and in general remained low during the study. All the common pests were found but only four were at a level where economic damage to the foliage resulted. Very few of the species were present in numbers sufficiently large for analysis of the factors influencing their population density or theirA list is given of those species which were sufficiently abundant to show that differences in preference for some cluster types over others is common.