Abstract: Tetramorium caldarium (Roger, 1857) is a tramp ant species originally from Africa that has dispersed around the world through human commerce. From 1862 to 1979, T. caldarium was considered a junior synonym of T. simillimum (Smith, 1851). To document the worldwide spread of T. caldarium, we compiled > 300 published and unpublished specimen site records. In addition, in order to assess their species boundaries, we examined the type specimens of T. caldarium and T. simillimum. We documented Tetramorium caldarium records from 67 geographic areas (countries, island groups, major Caribbean islands, and Us states), including several for which there are no previously published records: Austral Islands, Australia, Benin, Cameroon, Cayman Islands, Congo (Republic), Curaçao, Dubai, El Salvador, Gabon, Guadeloupe, Indonesia, Jamaica, Martinique, Namibia, Panama, Scotland, Senegal, South Africa, Tanzania, and Uganda. Tetramorium caldarium is truly cosmopolitan, with records spread across seven of the world's eight bioregions (all except the Antarctic, which has no ants). Tetramorium caldarium records are particularly common on Atlantic islands and from greenhouses and heated buildings in temperate Europe.