The Angerlloch (47°33'36.4"N, 011°17'12.9"E) is a relatively small karst cave located in the northern part of the Bavarian Alps, south of Walchensee, near the village of Obernach, at an altitude of approximately 942 m (a.s.l). The cave features seasonally flooded pools and passages, lower areas covered with sediment, an upper fossil network, and walls rich in troglophilic fauna. Its entrance is located in a steep, humid mountain forest, where a nearby stream originates but remains unconnected to the cave’s hydrographic network. Angerlloch is known to be a winter refuge for bats (Meining et al. 2009). On 9 October 2019 the temperature in the lower part of the cave was approximately 5.5 °C, and approximately 8.8 °C in the upper part.

The Schrecksattel Ice Cave (47°38'30.0"N, 012°47'57.3"E) is located near Bad Reichenhall, south of the village of Oberjettenberg, at an altitude of approximately 1,545 m (a.s.l). It is a karst cave located in the Schrecksattel massif and is known for its seasonal but persistent ice deposits. The study focused on the “old” part, an 80 m long sloping limestone corridor composed of rocks, clay, gravel, and permanent ice sheets, located above a coniferous forest and surrounded by grasses, mosses, and dwarf shrubs. On 10 October 2019, the temperature at the entrance was around 2.3 °C, gradually decreasing to 0.2 °C at the deepest point of the cave.

The Angerlloch and Schrecksattel caves were chosen for their easy access, low human disturbance, and proximity to the Bavarian Alps. The location of the Schrecksattel Ice Cave, close to Austrian caves known to harbour troglobitic fauna, increases the chances of finding related species (Christian and Spötl 2010). The main difference between the two targeted cavities is their altitude, 942 m for Angerlloch (mountain forest of beech and spruce) and 1545 m for Schrecksattel (subalpine spruce, shrubs and grasslands), which places them in different climatic and vegetation zones (Forster 2016).

Both caves were visited twice, once in early July (9/10 July 2019) and again in early October (9/10 October 2019). This double visit was necessary for two reasons: first, to collect a representative number of specimens, and second, because the first visit took place in summer and the second at the beginning of the cold period. Invertebrates were collected from the cave entrances. Small species were collected using exhausters, and larger species were collected directly into vials. The specimens were then transferred to 96% ethanol. In July, pitfall traps filled with saline solution were randomly placed in the caves (Fig. 1). Bait (cheese, sausage, moss, and dead wood) was placed on the ground around the trap openings. The traps were covered with stones to conceal them, while leaving the opening accessible. Four traps were placed inside the Angerlloch cave, two in the lower part and two in the upper gallery (Fig. 1). Five traps were placed inside the Schrecksattel Ice Cave (Figs 2, 3A).

The collected specimens were stored at the State Museum of Natural History Stuttgart. Specimens of the orders Coleoptera, Lepidoptera, Diptera, Trichoptera, Araneae, Opiliones, and Pulmonata were identified morphologically using a Nikon SMZ1270 binocular. Specimens from other groups were sent to specialists who confirmed the identifications (listed in the Acknowledgements).

Species diversity around cave entrances strongly influences the likelihood of accidental cave entry, as shown by the species numbers at the two sites studied. Angerlloch is surrounded by dense, species-rich forests, yielding greater nearby invertebrate diversity (Nagy et al. 2003). In contrast, the area around Schrecksattel has sparse subalpine vegetation, consisting mainly of mosses, lichens, grasses, dwarf shrubs, and scattered stunted trees, which are nutrient-poor and cannot support large invertebrate populations (Nagy et al. 2003). Consequently, fewer species can survive under harsher conditions than in the temperate forest surrounding Angerlloch. Most trogloxene species are represented by one or a few individuals, indicating accidental occurrence (Sket 2008). Apart from altitude, the main difference between Angerlloch and Schrecksattel in accessibility lies in entrance shape and position. Angerlloch’s wider, lower entrance, with soil and leaf litter extending into the cave, facilitates the entry of terrestrial fauna, whereas Schrecksattel’s narrow, elevated entrance reduces access for ground-dwelling species and flying insects (Throne et al. 1984; Fig. 5; Tables 1, 2).

Explaining the presence of troglophilic fauna in a cave is challenging, as these species are neither completely dependent on nor completely independent of underground habitats. Therefore, their occurrence depends on the ecology of each species. For example, Amilenus aurantiacus (Opiliones) uses caves for moulting and hibernating during winter, explaining its absence in Angerlloch in July (Mainz 1978). In contrast, Triphosa dubitata (Lepidoptera) uses caves throughout the year as resting sites, whereas Meta menardi (Araneae) spends most of its life inside caves, although juveniles disperse outside (Bartsch et al. 2001; Mammola and Isaia 2019). These differences explain the presence of troglophilic species in both caves despite their contrasting environmental conditions.

Resource-rich caves generally harbour more diverse communities dominated by troglophiles and trogloxenes, whereas troglobionts are more likely to persist in isolated resource-poor habitats (Latella and Stoch 2002; Sket and Culver 2004). This may explain the absence of troglobites in Angerlloch, where the entrance zone is dominated by troglophiles and trogloxenes. In contrast, the Schrecksattel Ice Cave contained three troglobitic species, including the CollembolaProtaphorura septempapillata. The isolated high-altitude location, colder climate, and dry surrounding subalpine habitat probably reduce gene flow with surface populations and favour the persistence of specialised cave fauna (Latella and Stoch 2002; Christiansen 2004; Sket 2008). Previously known only from the nearby Salzgrabenhöhle (Palissa 1986), the discovery of P. septempapillata in the Schrecksattel Ice Cave extends the known distribution of this remarkable cave-adapted species. The occurrence of several troglobitic taxa in the Schrecksattel Ice Cave is consistent with previous studies, suggesting that alpine karst systems acted as important refugia during past climatic fluctuations, allowing specialised subterranean fauna to persist in the Northern Calcareous Alps (Christian 2002; Christian and Spötl 2010).