Dynamics of ant activity under extreme climatic changes in 2024: effects of temperature  and humidity on Formica rufa and Lasius fuliginosus behavior

Global warming and extreme heatwaves, which can alter species distribution and ecosystem dynamics, have profound effects on forest ants. T‍his study investigated the impact of summer and autumn 2024 heatwaves on the activity, prey transport, and nest-building of Formica rufa Linnaeus, 1761 and Lasius fuliginosus (Latreille, 1798) in deciduous forests of Kyiv, Ukraine. Fieldwork was conducted from June to September 2024 in Holosiyivo Forest and the Feofaniya tract. Ant colonies were assigned to experimental plots, where logs were placed along foraging trails, or to control plots with unmanipulated ground-floor trails. The study included 10 F. rufa anthills for activity monitoring (five experimental, five control) and 16 F. rufa anthills for structural measurements (eight experimental, eight control), along with six L. fuliginosus colonies (three experimental, three control), with a total of 186 observations (120 for F. rufa, 66 for L. fuliginosus). Data on temperature and humidity were recorded to assess their influence on ant activity and nest structure. For F. rufa, trail activity showed a negative correlation with temperature (r = –0.308, p < 0.001) and a positive correlation with humidity (r = 0.355, p < 0.001), with multiple regression confirming humidity as the stronger predictor of activity (Wilks λ = 0.874, F = 17.02, p = 0.00042). Logs significantly enhanced foraging efficiency, particularly in July, doubling the activity and increasing prey transport by up to 178% compared to forest-floor trails. Anthill volumes declined from 2023 to 2024, with a smaller decrease in experimental nests (38%) than in controls (58.8%), and the number of branch nests was higher in experimental colonies (mean: 2.58 vs. 1.07). L. fuliginosus displayed lower thermal tolerance with almost complete cessation of prey transport by late season despite the structural advantages of log trails. These findings indicate that extreme heat and low humidity strongly suppress ant activity and prey transfer, but the structural enrichment of foraging trails mitigates some of those negative effects. F. rufa exhibited greater resilience than L. fuliginosus, maintaining higher activity and nest-building under heatwave conditions. The study highlights the importance of microhabitat structure in promoting colony performance and provides insights into the vulnerability of temperate forest ants under ongoing climate change.