Eleven synanthropic spider species, including seven alien ones, are known from the hothouses of the Botanic Garden, University of Turku, located on Ruissalo Island. Coleosoma floridanum (­Theridiidae), Howaia mogera (Nesticidae) and Triaeris stenaspis (Oonopidae) represent the northernmost known populations of these species in Europe. Coleosoma and Triaeris have lived in Ruissalo hothouses at least since the previous samplings in the 1990s, and Parasteatoda ­tepidariorum (Theridiidae) is known to have occurred there as early as the late 1950s. Some alien species, like Pholcus phalangiodes (Pholcidae), Uloborus plumipes (Uloboridae) and Howaia mogera have spread (i.e. been introduced) to Finland rather recently and they have been discovered in Ruissalo greenhouses in the last couple of decades. Conditions for spiders in this human-maintained small ecosystem are discussed.