The only National Inventory of red wood ants in Bulgaria was carried out about 50 years ago (1970–1973). Formica rufa Linnaeus, 1761, F. pratensis Retzius, 1783, F. lugubris Zetterstedt, 1838 and F. polyctena (as F. polyctena x rufa hybrid) were found in a current monitoring programme. This study presents data on their current distribution and nest density, and provides more details about the habitat requirements for conservation purposes. Field studies were carried out by the transect method along the main mountainous areas in Bulgaria. We found 256 nests of red wood ants along 172 transects. The most abundant species was F. lugubris, followed by F. rufa and F. pratensis. Among the environmental variables, the elevation, exposure, ecological groups of plants, stone cover, grass cover, canopy cover and forest age appeared as significantly related to the presence and nest density of red wood ants.

The Bulgarian myrmecofauna is one of the richest in the Balkans. This is a result of both the physicogeographical and paleoecological features of the area, as well as relatively well-studied fauna. The earliest myrmecological paper on Bulgarian fauna, listing 54 species, was published 130 years ago. The publication was later followed by numerous new faunistic records and three comprehensive reviews that significantly widened knowledge on the ant diversity from this country. The most recent checklist was released 12 years ago and considered 163 ant species from 40 genera.This work provides an updated checklist of 195 ant species from 43 genera occurring in Bulgaria. Since the last Bulgarian catalogue of ants, 44 species have been added, while 24 species have been synonymised or excluded after critical analysis of the last taxonomic revisions. Additionally, we discuss the status and distribution of 12 species described from Bulgaria, 23 species considered endemic and subendemic for this country, 19 species with conservation status and four non-native species.

The first record of alien terrestrial planaria Dolichoplana striata Moseley, 1877 (Platyhelminthes: Tricladida: Geoplanidae) in Bulgaria and on the Balkan Peninsula is reported. It was found in a greenhouse with exotic plants near Plovdiv City (Southern Bulgaria). The distribution of the invasive planarians has to be regularly monitored as they are responsible for a negative impact on the soil biodiversity.

The first record of the alien land flatworm Obama nungara (Platyhelminthes: Tricladida: Geoplanidae) in Bulgaria and on the Balkan Peninsula is presented. It was found in flower stocks and markets with exotic plants outside greenhouses near the cities of Plovdiv, Pazardzhik (Southern Bulgaria), and Burgas (Southern Black Sea) in 2024 and 2025. The locality in Burgas is the easternmost known in Europe. This is the second non-native terrestrial planarian species found in the country in the last two years. To confirm its identity with molecular data, mitochondrial COI sequences were obtained from eight specimens. Four unique genetic lineages were found in the Bulgarian material, comprising two clusters, each with two haplotypes. They correspond to the two clades ‘Argentina 1’ and ‘Argentina 2’, introduced to Europe. Both clades are known from France, Spain, and Italy. The species has likely reached Bulgaria through the intensive ornamental plant trade. The climatic conditions in Bulgaria seem suitable for successful overwintering outside greenhouses. Given the fact that O. nungara was officially added to the list of Invasive Alien Species of Union Concern in 2025 (EU 2025/1422), its presence in Bulgarian nurseries necessitates urgent phytosanitary oversight and measures. We recommend regular monitoring of invasive flatworm distribution, as they could contribute to a decline in soil biodiversity, primarily by reducing earthworm populations.

We give the results from the first investigation focused on the land snail fauna in Srebarna Nature Reserve in Bulgaria. A total of 23 localities were studied and 27 species of terrestrial gastropods were found, 23 of which were new observations for the Reserve.