Spiders are among the most common cave arthropods. Troglophile and troglobiont species are known among many spider families. In the former USSR countries troglophile spiders are represented by the following families: Agelenidae, Cybaeidae, Hahniidae, Linyphiidae, Nesticidae, Pholcidae, Tetragnathidae and Theridiidae (Turbanov et al. 2016). Within this territory, the highest species diversity was observed in the southern regions of the European part (the Carpathian Mountains and the Crimea) and in the Caucasus. A small number of spider species were reported from the caves in the Ural Mountains and only one species, from the Amur Oblast of Russia (Marusik 1987). To date, no spider species were recorded in special arachnological literature from the caves of Siberia, the largest part of Russia. While there are more than 1,400 caves in Siberia (Jubertie et al. 2016), only several species of Linyphiidae (Tenuiphantes alacris (Blackwall, 1853), Scotargus pilosus Simon, 1913 and Stemonyphantes sp.) were reported for the caves of Kamyshlinskoe Plateau in the Altai Mountains in the book “Atlas of the Caves of Russia” based on the records of I.S. Turbanov (Turbanov et al. 2019). In recent years, the author had an opportunity to visit six small caves in Southwestern Siberia. All caves are located in the Salair Ridge and in the Altai Mountains. Spiders were found in three out of six caves studied. The goal of this paper is to report all spider species found in these caves.

Specimen was photographed using an Olympus DP74 camera attached to an Olympus SZX16 stereomicroscope at the Altai State University. Photographs were taken in dish with black velvet paper on the bottom, filled with alcohol. Digital images were montaged using Helicon Focus software (https://www.photo-soft.ru/helicon-focus/). The data on the length and depth of caves are taken from the website “Caves. Information retrieval system” (https://speleoatlas.ru) and from the supplement to the book “The caves of Altai-Sayan mountainous region” (Tsykin et al. 1979). Material will be deposited in the Institute of Systematic and Ecology of Animals, SB RAS, Novosibirsk, Russia (ISEA).

The material was collected in three caves (Figs 9–10):

1. Russia, Novosibirsk Oblast, Barsukovskaya Cave, 54°22ʹN, 83°58ʹE, h=220 m, 29 August 2019, leg. A.A. Fomichev.

2a. Russia, Kemerovo Oblast, Gavrilovskaya II (Malaya Gavrilovskaya) Cave, 54°16ʹN, 85°52ʹE, h=260 m, 30 September 2019, leg. A.A. Fomichev.

2b. Same locality as above, 18 September 2020, leg. A.A. Fomichev, V.V. Sergeev, Yu.V. Dyachkov.

3. Russia, Altai Krai, Letuchikh Myshei Cave, 51°27ʹN, 83°07ʹE, h=350 m., 19 May 2020, leg. A.A. Fomichev, Yu.V. Dyachkov, E.Yu. Kulikov.

Three more caves were examined, but no spiders were found there (Figs 9–10):

4. Russia, Novosibirsk Oblast, Egor’evskaya (=Suenganskaya) Cave, 54°28ʹN, 84°35ʹE, h=270 m.

5. Russia, Kemerovo Oblast, Gavrilovskaya I (Bol’shaya Gavrilovskaya) Cave, 54°15ʹN, 85°52ʹE, h=270 m.

6. Russia, Altai Krai, Yashchur Cave, 51°10ʹN, 83°02ʹE, h=540 m.

Of six explored caves, spiders were found only in three, which are the most short and shallow: the Gavrilovskaya II Cave (length 32 m/depth 0 m (horizontal cave)/3 spider species), the Letuchikh Myshei Cave (87 m/0 m/3 species) and the Barsukovskaya Cave (195 m/19 m/1 species). These caves are relatively dry and due to their small length and depth they are warm in summer time. Caves, where spiders were not found, are longer and deeper: the Egor’evskaya Cave (208 m/33 m), the Gavrilovskaya I Cave (280 m/15 m) and the Yashchur Cave (404 m/69 m). These three caves are colder and much wetter. It can be assumed that in most caves in the Southwestern Siberia, temperatures are too low for spiders and the troglophilous spider fauna is scarce and distributed very locally.