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1. During the 2022/2023 austral winter, large swarms of Trichocera (Saltrichocera) maculipennis Meigen, 1818 (Diptera: Trichoceridae), were observed around house roofs in Puerto Williams (Navarino Island, southern Chile, 54° S). In January 2023, the presence of this species was also confirmed in Punta Arenas (53° S), with specimens collected within the Chilean Antarctic Institute warehouse facilities. 2. Trichocera maculipennis is native to the Holarctic region and became established on King George Island (South Shetland Islands, Maritime Antarctic) over 15 years ago. However, the species has not previously been reported from South America. 3. Taxonomic and molecular identification techniques were used to confirm the identity of the new specimens obtained from Navarino Island and Punta Arenas. Preliminary observations of the fly's habitat preferences and swarming behaviour in Puerto Williams are provided, as well as comparisons in wing morphometrics between flies from Puerto Williams and King George Island. 4. The fly's extensive distribution and high abundance in Puerto Williams are consistent with human-facilitated introduction and several years' establishment. 5. These findings emphasise the importance of implementing robust management strategies and biosecurity measures, particularly during transportation between logistical hubs in southern South America and the remote areas of the Cape Horn Biosphere Reserve and Antarctica.