The termites Reticulitermes santonensis (Rs) and R. lucifugus (Rl) were first regarded as different species (Feytaud, 1924) and then as the same species (Buchli, 1958). In later studies, Clement (1978, 1986) and Bagneres et al. (1990) used morphological and chemical (cuticular hydrocarbons) criteria to show that they actually are two distinct species. Feytaud (1924) and Bagneres et al. (1990) suggested that Rs could have originated from a North American population of R. flavipes that was introduced into Europe. The present study examined the distribution and reproductive cycle of Rs and an Rl sup-species, Rl grassei (Rlg), which are partly sympatric in southwest France. In the wild, Rs has an aggregated distribution related to human surroundings (past or present), i.e. populations are either dense or entirely absent. Conversely, Rlg is distributed randomly (from dense to few) throughout its range. For example, Rs is not found in towns within the Landes Forest, an area in southwest France that remained economically depressed and sparsely settled until after 1850 (Sargos, 1997), while Rlg is quite common there. Their respective reproductive strategies show that Rs populations spread through budding (swarms are scarce and many brachypterous nymphs and neotenics are found), whereas Rlg populations reproduce by both swarming and budding. It is likely that Rs is an introduced species and Rlg a native one that has reached its northern limits in France. A closer examination of North American Reticulitermes species, particularly R. flavipes, might reveal a relationship with the European species.