This article deals with the French botanist Nicolas Joseph Thiéry de Menonville who in 1777 went to Oaxaca (Mexico) in search of cochineal. Although cochineal was one of the Spanish Empire's best-kept secrets, he managed to go there, acquire knowledge about its cultivation from local planters, and smuggle the insects on cacti to Saint-Domingue, where he successfully raised them. His voyage is, thus, a paradigmatic case that illustrates how botanical knowledge and objects from local Indigenous farmers were transferred into the networks of European science. The analysis of how the botanist managed to gain access to a space and knowledge that was actually closed to him is embedded within a broader contextualization: starting with the examination of its main source, Voyage à Guaxaca, the article reconstructs the scientific and economic discourse that led Thiéry de Menonville to undertake his voyage. It concludes with contemporaries' evaluation of Thiéry de Menonville's transfer of knowledge about cochineal and its cultivation and the impact that his successful mission had on comparable endeavors.