NATURA SLOVENIAE 26(1): 17-28 Prejeto / Received: 5. 12. 2023 SCIENTIFIC PAPER Sprejeto / Accepted: 14. 5. 2024 DOI: 10.14720/ns.26.1.17-28 Biotehniška fakulteta Univerze v Ljubljani in Nacionalni inštitut za biologijo, Ljubljana, 2024 First records of the myrmecophilous spider Thyreosthenius biovatus (O. Pickard-Cambridge, 1875) for Slovenia and new Slovenian records for the myrmecophilous spider Mastigusa arietina (Thorell, 1871) Gregor BRAČKO, Rok KOSTANJŠEK University of Ljubljana, Biotechnical Faculty, Department of Biology, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia; E-mails: gregor.bracko@bf.uni-lj.si, rok.kostanjsek@bf.uni-lj.si Abstract. Ants from the Formica rufa group, also known as red wood ants, build large mound nests and play an important role in their environment, especially in forests. Their nests harbour a species rich and abundant myrmecophilous fauna, including a few European spider species. Myrmecophilous spiders in 40 nests of red wood ants from 25 sites were searched for in Slovenia. In each mound nest, four to five litres of material were collected, which were placed in a sifter, with the sifted material examined for the presence of spiders. Two myrmecophilous spider species were found in the nests: Thyreosthenius biovatus (fam. Linyphiidae), representing first records for Slovenia, and Mastigusa arietina (fam. Cybaeidae), previously known from several sites in western Slovenia, but never purposefully searched for in ant nests. The first spider species was found in half of the examined nests, belonging to all sampled species of red wood ants, most of them to F. aquilonia, and M. arietina was detected in 37.5% of the examined nests, belonging to F. aquilonia and F. lugubris. The two spider species are presumably not rare in Slovenia, especially in the areas with a high number of red wood ant nests. Key words: distribution, Formica, myrmecophiles, red wood ants, Slovenia, spiders Izvleček. Prve najdbe mirmekofilnega pajka Thyreosthenius biovatus (O. Pickard-Cambridge, 1875) za Slovenijo in nove slovenske najdbe mirmekofilnega pajka Mastigusa arietina (Thorell, 1871) – Mravlje iz skupine Formica rufa, poznane tudi kot rdeče gozdne mravlje, gradijo velika kopasta mravljišča in imajo v svojem okolju, še posebno v gozdovih, pomembno vlogo. Njihova mravljišča so zatočišča za vrstno bogato in številčno mirmekofilno favno, ki vključuje tudi nekaj evropskih vrst pajkov. Mirmekofilne pajke smo iskali v 40 mravljiščih rdečih gozdnih mravelj iz 25 lokalitet v Sloveniji. V vsakem od kopastih mravljišč smo vzeli od štiri do pet litrov materiala, ga dali v sejalnik in pregledali presejani material, ali so v njem pajki. V mravljiščih smo našli dve vrsti mirmekofilnih pajkov: Thyreosthenius biovatus (družina Linyphiidae), kar je prva najdba za Slovenijo, in Mastigusa arietina (družina Cybaeidae), ki je bila pred tem znana iz več lokalitet v zahodni Sloveniji, a nikoli ciljano iskana v mravljiščih. Prva vrsta pajka je bila najdena v polovici preiskanih mravljišč, ki so pripadala vsem vzorčenim vrstam rdečih gozdnih mravelj, vrsta M. arietina pa je bila odkrita v 37,5 % preiskanih mravljišč, ki so pripadala vrstama F. aquilonia in F. lugubris. Predvidevamo, da ti vrsti pajkov v Sloveniji nista redki, zlasti na območjih z velikim številom mravljišč rdečih gozdnih mravelj. Ključne besede: razširjenost, Formica, mirmekofili, rdeče gozdne mravlje, Slovenija, pajki 18 Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER NATURA SLOVENIAE 26(1): 17-28 Introduction Ant colonies can be considered as partially isolated ecosystem, their nests and surroundings are structured into many diverse microhabitats (Hölldobler & Wilson 1990). Nests are often rich in long-lasting resources, such as brood, retrieved or cultivated food, and nutrient-rich refuse material (Parmentier 2020). Nest temperature is often strictly regulated, and colonies are commonly defended by an army of workers. These nest microhabitats are occupied by various organisms, which show special adaptations to each of the niche in turn (Hölldobler & Wilson 1990). They exploit the nest’s resources and homeostatic conditions, at the same time, successful adaptation to the inner environment protects them from many predators that cannot penetrate this hostile space (Parmentier 2020). Myrmecophiles are organisms that must spend at least part of their life cycle with ant colonies (Hölldobler & Wilson 1990). There is hardly any terrestrial arthropod group that does not include at least few myrmecophiles (Seifert 2018). They can prey on ants in the vicinity or inside nest, they can act as scavengers in the nest or prey on other myrmecophiles, some are ectoparasites or endoparasites, or in case of trophobionts, supply their ants with food (honeydew) in exchange for protection against predators (Hölldobler & Wilson 1990; Seifert 2018). Myrmecophiles use different tactics to avoid ant attacks, either they are swift and escape, use repellent secretions or mechanical defensive structures. Others are ignored because of their slow movement or an apparently indistinct odour (chemical insignificance). Some myrmecophiles have evolved different types of chemical, morphological and behavioural adaptations that deceive the host ants, which accept them as members of the colony (Hölldobler & Wilson 1990; Parmentier 2020). Ant species with the largest colonies generally harbour the greatest diversity of myrmecophiles, as nests of large colonies provide a larger variety of microhabitats and have longer life span, so they can sustain larger and more stable populations of guests over longer time periods (Hölldobler & Wilson 1990; Kronauer & Pierce 2011). In Europe, ants from the Formica rufa group, also known as the red wood ants, usually build large mound nests constructed of dry plant material and soil particles (Fig. 1). They play an important role in their environment, especially in forests, where they are often ecologically dominant organisms and recognized as the keystone species and ecosystem engineers (Robinson & Stockan 2016; Sorvari 2016). Due to their large colonies and long life span, the nests of red wood ants harbour species rich and abundant myrmecophile fauna (Parmentier et al. 2014; Robinson et al. 2016). Myrmecophilous spiders are known in 13 spider families (Cushing 1997, 2012). They can prey on ants or other myrmecophiles that live in host nests. Females of several myrmecophilous spiders lay their egg sacs inside the chambers of ant nests. Some spiders may be occasional visitors to ant colonies, using the nests as temporary refuges. In Europe, three spider species are considered myrmecophilous and are found in the nests of red wood ants, specifically Mastigusa arietina (Thorell, 1871) (after a recent revision by Castellucci et al. (2023a) placed to fam. Cybaeidae), Thyreosthenius biovatus (O. Pickard-Cambridge, 1875) and Acartauchenius scurrilis (O. Pickard-Cambridge, 1873) (both fam. Linyphiidae) (Cushing 1997; Parmentier et al. 2014). Thyreosthenius biovatus is a myrmecophile in the nests of Formica species, mainly from the F. rufa group, while the other two species are also associated with species from other ant Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER 19 NATURA SLOVENIAE 26(1): 17-28 genera (e.g. Lasius, Tetramorium). In the nests, T. biovatus and M. arietina feed on other smaller myrmecophiles, ant eggs or ant prey (kleptoparasitism) (Parmentier et al. 2016a, 2018). Figure 1. Nest of Formica aquilonia (locality Rogla (SW of the parking area)) (photo: Gregor Bračko). Slika 1. Mravljišče vrste Formica aquilonia (lokaliteta Rogla (JZ od parkirišča)) (foto: Gregor Bračko). In Slovenia, the spider fauna of the Prealpine region can be considered relatively well researched, while other biogeographic regions still have a considerable potential for new records (Kostanjšek & Kuntner 2015; Kuralt & Kostanjšek 2016). The initial checklist of Slovenian spiders comprises 738 species belonging to 286 genera and 43 families (Kostanjšek & Kuntner 2015), and over 35 additional species were subsequently found (Kuralt & Kostanjšek 2016, 2019; Kuralt et al. 2024). Mastigusa arietina is known from several sites in western Slovenia (Polenec 1961, 1963, 1964, 1966, 1969, 1975, 1979, 1981, 1989; Novak 2005; Gorjan 2014). It is worth mentioning that another species in the genus, specifically M. macrophthalma (Kulczyński, 1897), has also been recorded from several locations in western Slovenia (Kostanjšek & Kuntner 2015). Since the species differ from each other only in position and dimension of the posterior median eyes, it is not unlikely that the two forms represent separate races, rather than species (Roberts 1995). The taxonomic status of M. macrophthalma is therefore debated and the genus is currently under revision (Castellucci et al. 2023a). Two other myrmecophilous spiders, Thyreosthenius biovatus and Acartauchenius scurrilis, have so far never been recorded from Slovenia. Our sampling of arthropods in the mound nests of the Formica rufa group at several sites in Slovenia yielded the first records of Thyreosthenius biovatus for the country and several new records of Mastigusa arietina. 20 Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER NATURA SLOVENIAE 26(1): 17-28 Materials and methods In the period from June to October 2023, we sampled arthropods in the mound nests of the Formica rufa group. Forty nests were examined at 25 sites, mainly in the northern parts of Slovenia (Tab. 1). Table 1. Information on sampled nests of red wood ants (Formica rufa group) in Slovenia in 2023. Tabela 1. Podatki o vzorčenih mravljiščih rdečih gozdnih mravelj (skupina Formica rufa) v Sloveniji leta 2023. Nest no. Formica species Locality WGS84 coordinates [dec. degr. N/E] Altitude [m] Habitat Date of sampling 1 F. aquilonia Vršič (near Erjavčeva koča) 46.4385/13.74817 1530 Alpine grassland with Larix decidua 12.9.2023 2 F. polyctena Kranjska Gora (Golf Course) 46.4885/13.80517 780 belt of trees next to golf course 12.10.2023 3 F. lugubris Vrata Valley (NE of Aljažev Dom) 46.41317/13.85 980 pasture with isolated spruces 12.10.2023 4 F. lugubris Vrata Valley (NE of Aljažev Dom) 46.41317/13.85 980 edge of spruce forest 12.10.2023 5 F. aquilonia Pokljuka (W of Planina Praprotnica loc. 1) 46.327/13.91283 1230 edge of spruce forest 23.7.2023 6 F. aquilonia Pokljuka (W of Planina Praprotnica loc. 1) 46.327/13.91283 1230 edge of spruce forest 23.7.2023 7 F. aquilonia Pokljuka (W of Planina Praprotnica loc. 2) 46.32567/13.9145 1230 pasture with isolated spruces 23.7.2023 8 F. aquilonia Pokljuka (W of Planina Praprotnica loc. 2) 46.32567/13.9145 1230 open mixed forest 23.7.2023 9 F. polyctena S of Matavun near Divača 45.661/13.992 410 mixed forest 27.9.2023 10 F. lugubris Soriška Planina (NW of Lajnar) 46.24433/14.00667 1280 grassland with isolated spruces 20.8.2023 11 F. lugubris Soriška Planina (SW of Lajnar) 46.2415/14.00767 1280 open spruce forest 20.8.2023 12 F. lugubris Soriška Planina (SW of Lajnar) 46.2415/14.00767 1280 open spruce forest 20.8.2023 13 F. lugubris Ljubelj Pass (W of parking area) 46.43183/14.25917 1060 edge of mixed forest along the path 12.10.2023 14 F. rufa 2.5 km NW of Podljubelj near Tržič 46.42033/14.26933 810 edge of mixed forest along the path 12.10.2023 15 F. polyctena Krancelj near Škofja Loka 46.162/14.30133 460 edge of mixed forest 13.8.2023 16 F. rufa 1 km SW of Golnik near Kranj 46.31917/14.32383 450 edge of mixed forest along the road 14.10.2023 17 F. rufa 1.5 km N of Bevke near Vrhnika 45.99817/14.36167 300 spruce forest 16.7.2023 18 F. rufa 1.5 km N of Bevke near Vrhnika 45.99817/14.36167 300 edge of spruce forest 16.7.2023 Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER 21 NATURA SLOVENIAE 26(1): 17-28 Nest no. Formica species Locality WGS84 coordinates [dec. degr. N/E] Altitude [m] Habitat Date of sampling 19 F. rufa × polyctena 1.5 km N of Bevke near Vrhnika 45.99817/14.36167 300 edge of spruce forest 16.7.2023 20 F. lugubris Menina Planina (NW area) 46.26883/14.805 1370 edge of spruce forest 8.7.2023 21 F. lugubris Menina Planina (NW area) 46.26883/14.805 1370 edge of spruce forest 8.7.2023 22 F. lugubris Menina Planina (NW area) 46.26883/14.805 1370 edge of spruce forest 8.7.2023 23 F. aquilonia Menina Planina (0.5 km NW of the hut) 46.26433/14.81583 1420 open spruce forest 8.7.2023 24 F. aquilonia Menina Planina (0.5 km NW of the hut) 46.26433/14.81583 1420 open spruce forest 8.7.2023 25 F. aquilonia Menina Planina (0.7 km W of the chapel) 46.24517/14.83117 1310 edge of spruce forest 8.7.2023 26 F. aquilonia Rogla (SW of the parking area) 46.44933/15.32033 1430 open spruce forest 10.6.2023 27 F. aquilonia Rogla (SW of the parking area) 46.44933/15.32033 1430 open spruce forest 10.6.2023 28 F. aquilonia Rogla (SW of the parking area) 46.44933/15.32033 1430 open spruce forest 10.6.2023 29 F. aquilonia Rogla (S of the parking area) 46.44667/15.334 1350 spruce forest 10.6.2023 30 F. aquilonia Rogla (S of the parking area) 46.44667/15.334 1350 spruce forest 10.6.2023 31 F. aquilonia Pohorje (0.5 km N of Jurgovo) 46.46367/15.37267 1240 edge of spruce forest 24.6.2023 32 F. aquilonia Pohorje (1 km S of Lukanja) 46.432/15.39383 1030 edge of spruce forest 24.6.2023 33 F. aquilonia Pohorje (1 km S of Lukanja) 46.432/15.39383 1030 edge of spruce forest 24.6.2023 34 F. aquilonia Pohorje (Osankarica) 46.45867/15.42683 1200 edge of spruce & pine forest 24.6.2023 35 F. aquilonia Pohorje (Osankarica) 46.45867/15.42683 1200 edge of spruce forest 24.6.2023 36 F. aquilonia Pohorje (Areh, near Ruška koča) 46.49717/15.51317 1200 edge of spruce forest 1.8.2023 37 F. aquilonia Pohorje (Areh, near Ruška koča) 46.49717/15.51317 1200 edge of spruce forest 1.8.2023 38 F. lugubris Mariborsko Pohorje (1.5 km SW of Hotel Bellevue) 46.50467/15.5625 1060 edge of mixed forest 1.8.2023 39 F. lugubris Mariborsko Pohorje (slope NE of Hotel Bellevue) 46.51483/15.58083 1030 edge of spruce forest 1.8.2023 40 F. rufa 1.5 km S of Apače near Gornja Radgona 46.68467/15.906 220 mixed forest 2.8.2023 22 Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER NATURA SLOVENIAE 26(1): 17-28 Sampling of spiders in the nests of the Formica rufa group was carried out by digging by hand inside the mound and collecting four to five litres of nest material. This was placed in the litter sifter with 5 × 5 mm mesh. The sifted material was placed on a white sheet and carefully examined for the presence of spiders (juvenile or adult specimens) and other arthropods. Detected specimens and some host ants were collected and preserved in 96% ethanol. After inspection, the nest material, together with ants, was returned to the sampled nest. Spiders were identified using on-line taxonomic key Spiders of Europe (Nentwig et al. 2023), and Formica ants using key in Seifert (2018). Results and discussion Spiders and other arthropods were examined in 40 nests of the Formica rufa group: 20 examined nests belonged to F. aquilonia, 11 to F. lugubris, 5 to F. rufa, 3 to F. polyctena, and one colony was identified as a hybrid F. rufa × polyctena (Tab. 1). Our search for the red wood ants nests was not random, as we focused mainly on the areas where these nests are more common, specifically in the Alpine and Prealpine regions of Slovenia above 1,000 m altitude. In these areas, F. aquilonia and F. lugubris are by far the commonest species of the F. rufa group (Bračko 2023). Thyreosthenius biovatus (Fig. 2A) was found at 13 different sites in 20 nests (half of all examined nests), belonging to all sampled species of red wood ants, most of them to F. aquilonia (Figs. 3, 4). Mastigusa arietina (Fig. 2B) was found at 11 sites in 15 nests (37.5% of the nests examined), but only in F. aquilonia and F. lugubris (Figs. 3, 4). Of the two most frequently sampled ant species, i.e. F. aquilonia and F. lugubris, the first seems to be preferred by both myrmecophilous spiders. Thyreosthenius biovatus was recorded in 65% of F. aquilonia nests and in 36% of the F. lugubris nests examined, while Mastigusa arietina was found in 60% of the F. aquilonia and in 27% of the F. lugubris nests examined. In seven cases, both spider species were present in the same F. aquilonia nest, which was not detected in F. lugubris or any other sampled wood ant species. The reason for this preference could be that at the visited sites with F. aquilonia, the nests of this species were very numerous, especially in the area of Rogla and Pohorje, which enables larger populations of myrmecophiles. Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER 23 NATURA SLOVENIAE 26(1): 17-28 Figure 2. Thyreosthenius biovatus female (A) and Mastigusa arietina female (B) from locality Pohorje (1 km S of Lukanja) (photo: Gregor Bračko). Slika 2. Thyreosthenius biovatus samica (A) in Mastigusa arietina samica (B) z lokalitete Pohorje (1 km J od Lukanje) (foto: Gregor Bračko). Figure 3. Localities of the spider species Thyreosthenius biovatus and Mastigusa arietina in Slovenia (the numbers next to symbols refer to successive nest numbers as shown in Tab. 1; the different colours of the symbols refer to different Formica host species). Slika 3. Najdišča vrst pajkov Thyreosthenius biovatus in Mastigusa arietina v Sloveniji (številke ob simbolih se nanašajo na zaporedne številke mravljišč, kot so prikazane v Tab. 1; različne barve simbolov se nanašajo na različne gostiteljske vrste Formica). A B 24 Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER NATURA SLOVENIAE 26(1): 17-28 Figure 4. The presence of two myrmecophilous spider species (A – Thyreosthenius biovatus, B – Mastigusa arietina) in the examined ant nests of the Formica rufa group (percentage according to all examined nests (n = 40)). Slika 4. Prisotnost dveh vrst mirmekofilnih pajkov (A – Thyreosthenius biovatus, B – Mastigusa arietina) v preiskanih mravljiščih mravelj skupine Formica rufa (odstotek glede na vsa preiskana mravljišča (n = 40)). In a similar study conducted in the Italian Alps, the two myrmecophilous spider species were found in the nests of F. aquilonia (most frequently), F. lugubris, F. paralugubris (a species not known for Slovenia), F. polyctena and F. rufa (Castellucci et al. 2022). In contrast to our study, M. arietina was more common in the nests than T. biovatus (found in 81% of the examined nests compared to 31% for T. biovatus). Prior to their study, there had been no literature records of M. arietina from nests of F. aquilonia, F. lugubris and F. paralugubris, and T. biovatus had not been recorded from the nests of F. aquilonia. According to Castellucci et al. (2022), this is probably due to taxonomic uncertainties, as in previous literature many of the red wood ants were not correctly identified and were often given as Formica rufa. Our results confirm the conclusions of Castellucci et al. (2022), as the two spider species were regular guests in the F. aquilonia and F. lugubris colonies examined. Despite long history of spider research in Slovenia, T. biovatus had not been recorded previously from the country, presumably due to absence of sampling in the mounds of red wood ants. Our results indicate that this species is not rare in Slovenia. We found it in half of the examined nests, which belonged to all of the studied ant species. The localities of T. biovatus are situated mainly in the Alpine and Prealpine parts of the country, but also in the Submediterranean region (locality Matavun). Similarly to T. biovatus, M. arietina was never searched for inside red wood ant nests, or the nest of other ant species, despite of being aware of its common association with ants (Polenec 1964). Records of the species by Polenec and other authors (summarized in Kostanjšek & Kuntner 2015) originate mainly from sampling of M. arietina in pitfall traps or sifting the leaf litter, presumably close to host ant nests. This spider species is less integrated into wood ant colonies compared to T. biovatus (Parmentier et al. 2014, 2016b; Nentwig et al. 2023) and is probably more active also in the vicinity of the host nests. The results of the present study show that M. arietina is common in the nests of F. aquilonia and not rare in the nests of F. lugubris, which means that this spider species is probably widespread in the Alpine and at higher altitudes of Prealpine regions of Slovenia, where the two host ant species are common. 32.5% 10% 2.5% 2.5%2.5% 50% F. aquilonia F. lugubris F. polyctena F. rufa F. rufa x polyctena absent 30% 7.5%62.5% F. aquilonia F. lugubris absent A B Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER 25 NATURA SLOVENIAE 26(1): 17-28 Similar to some other European countries, e.g. Spain (Castellucci et al. 2023b), Denmark (Scharf & Gudik-Sørensen 2006), Belgium (Parmentier et al. 2022) and Italy (Castellucci et al. 2022), our study confirms that additional approaches in fieldwork, such as sampling for spiders in ant nests, can provide new records of T. biovatus and M. arietina and reveal that these spiders are not as rare as previously thought. Myrmecophiles have never been systematically sampled in Slovenia, so many species are missing from the checklists. This should be improved by future studies on these guests of ant colonies. Povzetek Mravljišča in njihovo neposredno okolico sestavlja veliko raznolikih mikrohabitatov, ki jih poseljujejo različni organizmi. Mirmekofili so organizmi, ki morajo vsaj del svojega življenja preživeti s kolonijami mravelj (Hölldobler & Wilson 1990). Zlasti velike, dolgoživeče kolonije vsebujejo vrstno bogato in številčno favno mirmekofilov (Hölldobler & Wilson 1990; Kronauer & Pierce 2011). Med takimi so tudi rdeče gozdne mravlje (skupina Formica rufa), ki gradijo velika kopasta mravljišča in imajo v okolju, ki ga poseljujejo, zelo pomembno vlogo, zato so pogosto prepoznane kot ključne vrste in ekosistemski inženirji (Robinson & Stockan 2016; Sorvari 2016). Med mirmekofili, ki jih srečamo v mravljiščih rdečih gozdnih mravelj, so tudi pajki, v Evropi predvsem vrsti Thyreosthenius biovatus (O. Pickard-Cambridge, 1875) (družina Linyphiidae) in Mastigusa arietina (Thorell, 1871) (družina Cybaeidae) (Cushing 1997; Parmentier et al. 2014). V kolonijah gozdnih mravelj plenita bodisi druge manjše mirmekofilne vrste, jajca mravelj ali pa mravljam kradeta njihov plen (Parmentier et al. 2016a, 2018). Kljub relativno dolgi zgodovini raziskav favne pajkov v Sloveniji, vrsta T. biovatus pri nas še ni bila zabeležena, vrsta M. arietina, ki je sicer poznana iz več lokalitet v zahodni Sloveniji, pa nikoli ni bila ciljano vzorčena v mravljiščih (Kostanjšek & Kuntner 2015). V obdobju od junija do oktobra 2023 smo sistematično iskali členonožce v mravljiščih rdečih gozdnih mravelj. Vzorčili smo na 25 lokalitetah, predvsem v severnem delu Slovenije. Iz kopastega dela mravljišča smo vzeli od štiri do pet litrov materiala in ga dali v sejalnik, presejani material skrbno pregledali in iz njega pobrali pajke ter druge členonožce. Skupno smo pregledali 40 mravljišč rdečih gozdnih mravelj. Največ pregledanih mravljišč je pripadalo vrsti F. aquilonia, sledile so F. lugubris, F. rufa, F. polyctena, eno kolonijo pa smo določili kot hibrid F. rufa x polyctena. V naši raziskavi smo našli obe omenjeni vrsti mirmekofilni pajkov. Thyreosthenius biovatus smo odkrili v polovici od vseh preiskanih mravljišč, največkrat pri F. aquilonia, sicer pa smo jo zabeležili pri vseh vzorčenih vrstah rdečih gozdnih mravelj. Mastigusa arietina smo našli v 37,5 % pregledanih mravljišč, in sicer le pri vrstah F. aquilonia in F. lugubris. V sedmih primerih smo v istem mravljišču (v vseh primerih vrste F. aquilonia) zabeležili obe vrsti pajkov. Izmed dveh vrst mravelj, ki sta bili najpogosteje vzorčeni (F. aquilonia in F. lugubris), v naši raziskavi obe vrsti pajkov dajeta prednost gostovanju pri F. aquilonia. Z našo raziskavo smo prvič pri nas ciljano ugotavljali prisotnost mirmekofilnih pajkov v mravljiščih rdečih gozdnih mravelj. Podatki raziskave nakazujejo, da obe vrsti pajkov v Sloveniji nista redki, še posebno v alpski regiji in v višjih predelih predalpske regije, kjer so rdeče gozdne mravlje (predvsem vrsti F. aquilonia in F. lugubris) precej pogoste. 26 Gregor BRAČKO & Rok KOSTANJŠEK: First records of the myrmecophilous spider ... / SCIENTIFIC PAPER NATURA SLOVENIAE 26(1): 17-28 References Bračko G. 2023. Atlas of the ants of Slovenia. Biotechnical Faculty, Ljubljana. Castellucci F, Schifani E, Luchetti A, Scharff N. 2022. New association between red wood ant species (Formica rufa group) and the myrmecophilic spiders Mastigusa arietina and Thyreosthenius biovatus. Bulletin of Insectology. 75(2): 231-238. Castellucci F, Scharff N, Luchetti A. 2023a. Molecular systematics and phylogenetics of the spider genus Mastigusa Menge, 1854 (Anraneae, Cybaeidae). 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Cambridge: Cambridge University Press. p. 264-286. https://doi.org/10.1017/CBO9781107261402.013 © 2024 Gregor Bračko, Rok Kostanjšek To je prostodostopen članek, objavljen pod določili licence Creative Commons Priznanje avtorstva 4.0 Mednarodna, ki dovoljuje neomejeno rabo, razširjanje in kopiranje v kakršnemkoli mediju ter obliki, pod pogojem, da sta navedena avtor in vir. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.