Summary The arthropod fauna of larches, Larix decidua, from four different E. Alpine localities is studied and compared. In particular, the fauna of a single tree growing in the isolation of a city is compared with that of larches in different wooded sites. Larch pests as well as indifferent larch inhabitants and their biological controlling agents are studied. The following are dealt with: 1. the larch mining moth, Coleophora laricella Hb., and its parasites; 2. the larch needle tortrix, Tmetocera lariciana Heim., development, number of generations and parasites; 3. the larch bark tortrix, Laspeyresia grunertiana Rtzb., larval development in bark mines, parasites; 4. the larch bud midge, Dasyneura laricis F. W. It was possible, for the first time, to rear a parasite of this insect, a Torymus species, the development of which is described; 5. Adelges laricis Vall., the life cycle is described; 6. Sacchiphantes viridis Ratz. The summer virginogeniae of this species were also found on larch, for the first time; 7. several species of Cinarines are described as honeydew producers; 8. Syrphid larvae, Neuroptera, Coccinellidae, Miridae, Anthocoridae, Chalcididae and Aphididae were observed and are described as biological controlling agents of Cinarines; 9. a new species of parasite was reared from the Neuropteran Conwentzia pineticola End., the description was prepared by Ch. Ferriere and is included; 10. Eriophyes pini var. laricis Nalepa. Gall formation and the differences from Dasyneura galls are noted; 11. the larch thrips, Taeniothrips laricivorus Krat., its occurrence in western Wienerwald is recorded; 12. the larch bark beetle, Ips cembrae Heer, adult feeding prior to maturity appears to be regulary on young shoots. Notes are also given on the spider fauna and the bark fauna. At the end, all species found on larch and their distribution in the localities are given in tabular form. A comparison between the fauna of the city larch and that of forest larches shows that only comparatively few species are restrictet to the forest biozonose and many species can maintain themselves also in isolation.