On the Reasons for Limenitis sydyi (Lepidoptera, Nymphalidae) Expansion in Transbaikal

In 1990–2020, long-term field observations in the Transbaikal region (Siberia, Russia) revealed a range expansion of the nemoral butterfly species Limenitis sydyi (Lepidoptera, Nymphalidae) further into Siberia (120° E to 110° E). This species had not been registered to the west of the Chita–Kyra longitudinal line (112° E) before the 2000s, but subsequently became rather common in the environs of the city of Chita. Its first occurrence in the Republic of Buryatia (110° E) was recorded in 2012. This species prefers the sparse-growth forests dominated by larch (Larix sp.) and birch (Betula pendula Roth) that commonly occur in the second-order river valleys at elevations of 400–600 m, whereas the broader and narrower river valleys are only marginally suitable for this nemoral species. Additionally, rather high air humidity levels are critical to L. sydyi during particular periods of its life cycle (May–June and September), as well as a snow depth of at least 10–20 cm.