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Conducting a repeat study of the presence of mound-building red wood ants (Formica rufa group) after a period of 30 years has rarely been done in Europe. From 1990 to 2020 such a study was done in an intensively used agricultural landscape with fragments of forest in the South-Eastern part of The Netherlands. In 1990, 280 nest mounds of three species of red wood ants and a hybrid were found in the forests and along forest edges. The highest occupancy was in forests of > 25 ha. The connectivity between the forest fragments mainly determined their presence. In 2020, only 160 nest mounds were found. The development of the colonies differed for Formica polyctena Förster, 1850 (slight decrease), F. rufa Linnaeus, 1761 (substantial increase) and F. pratensis Retzius, 1783 (strong decrease). The differences between the species in this highly fragmented landscape may be due to differences in their colonization strategies of either nest splitting or producing swarms of young queens. Furthermore, the analyses show that the type of environment (in a forest or along a forest edge) determines the probability of extinction or settlement. There is a need to undertake management measures to prevent the extinction of species of red wood ants in the area studied. These measures include creating small clearings in dense forests, reducing shading due to overgrowing shrubs or herbaceous plants, and creating buffer zones around intensively manured fields. More long-term monitoring is needed in Europe to compare the circumstances in different regions, detect trends and evaluate the effects of protection measures. more...