Collapse of the invasive garden ant, Lasius neglectus, populations in four European countries

© 2016, Springer International Publishing Switzerland. The invasive garden ant Lasius neglectus (Hymenoptera: Formicidae) has been spreading rapidly in Europe ever since the 1990s. This ant established enormous supercolonies in many European cities and poses a serious threat to the local native faunas. The spread of this species has not slowed down in the last decades, but in the recent years the sizes of the known L. neglectus populations have generally been declining or have stagnated. For 29 supercolonies checked in four countries, in 10 cases L. neglectus individuals have not been found on the former area of their occurrence. On the other hand, only two supercolonies have expanded. In this paper, we summarize these monitoring data collected by the personal independent, diligent monitoring activities of myrmecologists on populations of the invasive garden ant in Bulgaria, Hungary, Poland and Spain. The reasons for this collapse are thought to be: (1) depletion of the local resources, (2) gradation of pathogens and (social)parasites, (3) climatic factors, (4) intra-population mechanisms, (5) confrontation with highly competitive native species, and (6) lack of suitable nesting microhabitats. As similar phenomena were observed in the cases of supercolonies of other invasive ant species, it seems that they decline more generally than has been thought.