Abstract: Invasive ant species represent a serious threat to many ecological communities, often causing decreases in the abundance, species richness and diversity of native ants and other arthropods. The invasive garden ant, Lasius neglectus Van Loon, Boomsma & ANDRÁSFALVY, 1990, is an invasive tramp species that forms dense supercolonies. We studied the ecological impacts of the type supercolony of this species on other ants and surface-active arthropods in Budatétény, Budapest, Hungary. Arthropod abundance, species richness and diversity were estimated by using pitfall traps. The L. neglectus supercolony radically changed the composition of the arthropod assemblage. The diversity of total arthropods, Coleoptera and other Formicidae was lower in the areas with L. neglectus supercolony than in the control areas. The presence of L. neglectus caused a significant reduction in species richness of Isopoda and other Formicidae, but a significant increase in Hemiptera. Lasius neglectus had a significant negative effect on the abundance of the arthropod species Armadillidium vulgare (Latreille, 1804) (Isopoda: Armadillidiidae), Trachelipus rathkii (Brandt, 1833) (Isopoda: Trachelipodidae), Harpalus rubripes (Duftschmid, 1812) (Coleoptera: Carabidae), Ocypus olens (O. MÜLLER, 1764) (Coleoptera: Staphylinidae), Galeruca tanaceti (Linnaeus, 1758) (Coleoptera: Chrysomelidae), Myrmica sabuleti Meinert, 1861 (Hymenoptera: Formicidae), Tetramorium cf. caespitum (Linnaeus, 1758) (Hymenoptera: Formicidae), Tapinoma ambiguum Emery, 1925 (Hymenoptera: Formicidae), Lasius niger (Linnaeus, 1758) (Hymenoptera: Formicidae) and Formica sanguinea Latreille, 1798 (Hymenoptera: Formicidae) and total Isopoda. However, there was a significant increase in numbers of Kalama tricornis (Schrank, 1801) (Heteroptera: Tingidae), Lampyris noctiluca (Linnaeus, 1767) (Coleoptera: Lampyridae), Dermestes laniarius Illiger, 1801 (Coleoptera: Dermestidae), Hahnia nava (Blackwall, 1841) (Araneae: Hahniidae), and in Oribatida, Cicadellidae (Hemiptera) and larvae of Clytrinae (Coleoptera: Chrysomelidae).