First winter record of Latrodectus mirabilis (Araneae: Theridiidae) in arid Patagonia: a consequence of climate change and urbanization?

Cases of araneism reported in the province of Chubut (Argentina) have tripled in the last two decades, and almost 80 % of them involve Latrodectus mirabilis (Holmberg) (Araneae: Theridiidae). According to descriptions of the life cycle of this species in Argentina, the low temperatures typical of autumn-winter cause the death of all adult spiders, so that no adult specimens of L. mirabilis are observed in winter. Field samplings, observations by the Grupo de Entomología Patagónica (GENTPAT, IPEEC CCT CENPAT CONICET), and citizen reports for more than 15 years suggested a similar cycle in northeastern Patagonia. However, for the last three consecutive years, we have recorded adult females in the field throughout the Patagonian winter. Some of these individuals even survived the winter and were alive the following spring. The purpose of this note is to report the field presence of adult female specimens of L. mirabilis in the outskirts of the city of Puerto Madryn (Chubut, Argentina) during the last three consecutive winters corresponding to the years 2021, 2022 and 2023; and to note that at least two of them survived the winter, arriving alive (and in good condition) the following spring. Given the medical importance of this spider, the publication of this information, the context of the findings, and their ecological implications will help to prevent its spread and reduce the likelihood of accidents.