Preliminary results of the monitoring of protected red wood ants in Rila Mountain, Bulgaria

Abstract

This study aimed to assess the present distribution of red wood ant species and changes in their nest density over a period of eight years in the area of Rila Mt, Bulgaria. One of the sampling areas was the Parangalitza Biosphere Reserve, the nation’s second oldest protected area. The other two sites are Rila Monastery region and Samokov region. Field monitoring via transect sampling was conducted in 2014 and 2022. We marked 35 nests along 29 transects in 2014 and 76 nests along 27 transects in 2022 of the red wood ants Formica rufa Linnaeus, 1761, F. lugubris Zetterstedt, 1838, F. pratensis Retzius, 1783, and F. exsecta Nylander, 1846, the latter of which is not a member of the rufa group. The most abundant species was F. rufa, followed by F. lugubris, F. pratensis, and F. exsecta. The nest density of F. rufa and F. pratensis decreased in some of the revisited transects after 8 years, which can be explained by increased shading of their habitats. Monitoring is recommended at least every 5 years to detect trends in red wood ant populations and evaluate the effects of protection measures.