Abstract This two-folded contribution firstly addresses the little-known history of an agricultural utopia that took over the newly born Belgium. The history of the Belgian sericultural utopia is not anecdotal, however, it was based on the conviction that it was possible to acclimatize exotic species. This conviction has a long history that is depicted in the second part of this research. The permanence in time of this hope is explained by various factors: famous supporters, a lexical fog, experiments considered successful, routines, agricultural crisis, etc. They kept alive the dream of acclimatization carried out by the French Enlightenment, but not only. Yet, in the first decades of the nineteenth century, the zealots of the famous André Thouin confronted those—early phytogeographers, or not—who rejected acclimatization more often. It might even be that biological nationalism militated against acclimatization, as showed the International Congress of Horticulture in Brussels (1864), which constitutes the chronological milestone of this research.