Four spider species were found in the artificial tropical ecosystem of the Biodôme de Montréal (Québec, Canada): Steatoda triangulosa (Theridiidae), previously reported from Québec and Ontario, Coleosoma floridanum (Theridiidae), Theridion melanostictum (Theridiidae), and Scytodes fusca (Scytodidae), which have never been recorded in Québec. These species were likely to have been imported from Florida along with plants used in the reconstruction of this tropical ecosystem. The occurrences of these species demonstrate an inefficiency in quarantine procedures. Each species is diagnosed and illustrated in order to facilitate their monitoring and possible invasion of natural habitats from this source of introduction.