Long-distance dispersal of migrant butterflies to the Arctic Ocean islands, with a record of Nymphalis xanthomelas at the northern edge of Novaya Zemlya (76.95°N)

Although migrant butterflies are rare (or sporadically seen) guests on the Arctic Ocean islands, there is a slowly growing dataset on repeated occurrences of these insects in insular tundra and polar deserts. Altogether six long-distance migrant butterfly species were found to cross wide marine barriers north of the Arctic Circle (66.56°N), i.e. Vanessa atalanta, V. cardui, Nymphalis antiopa, N. xanthomelas, Aporia crataegi, and Pieris napi. Migrant individuals of V. cardui discovered on Svalbard (up to 78.27°N in 1978) reflect the farthest dispersal event of butterflies to the Arctic ever reported. Our record of N. xanthomelas at the northern margin of Novaya Zemlya (76.95°N) represents the northernmost finding of this species globally, reflecting the world's second farthest record of northern poleward immigration of butterflies. This occurrence coincides with an exceptionally warm summer season, when the third highest July and second highest August air temperature occurred (since global records began in 1880). Furthermore, the immigration into Novaya Zemlya coincides with a population explosion and massive expansion of N. xanthomelas in Siberia in 2019–2020. Our air current reconstructions indicate that this species most likely immigrated into Novaya Zemlya from mainland regions situated south-southeast (Polar Urals, Yugorsky Peninsula, and western Yamal) and east (Taymyr) of the archipelago. Overall, our findings reveal that long-distance dispersal events of butterflies to the Arctic islands are always linked to massive expansions of the corresponding species in mainland areas.