Expansion or recolonization: Distribution and ecology of the pontic-mediterranean species of genus Acrotylus (Orthoptera) at the northern border of their range

Several thermophilous insect species have shown northward expansion in recent decades, and for some, it is only a matter of the recolonization of historic sites. Acrotylus insubricus and A. longipes are pontic-mediterranean species, and their northern edge is in Central Europe (Slovakia). Between 1890 and 1962, these species were known as rare in southern Slovakia, with A. insubricus found at five sites during that period and A. longipes found only once (1961) in southeastern Slovakia. Despite increased sampling efforts in Slovakia after 1997, A. insubricus was not documented between 1962 and 2019, and A. longipes was not found between 1961 and 2023. In 2016, we began regularly checking 53 sandy habitats in southern Slovakia; A. insubricus was found abundant in two sites in 2019 and in nine sites in 2024 and 2025, while A. longipes was found abundant in two sites in 2023 (Aug 21-Nov 3) and in three in 2024 and 2025 (Jun 21–Oct 25), always accompanied by A. insubricus . Recently, the edge of the northernmost range of A. insubricus in Central Europe was 48.53°N, and for A. longipes , it was 48.40°N. In this paper, we describe the distribution, abundance, phenology, and habitat of both species. Regarding habitat, A. longipes needs sandy bare ground with sparse psammophilous vegetation and impacted frequently by human interference, while A. insubricus is more eurytopic and also occurs on rocky steppes. We found only A. insubricus adults overwintering in all nine sites, but never A. longipes , which is different behavior than that of these species in the southern parts of the range. We suggest that A. insubricus and A. longipes have recolonized historical sites and spread into sandy, human-disturbed habitats.