This article aims to present an important article by Raymond Ruyer, published in 1959, in which the author deals with instinct and the theory of thematism in Bergson, considering the case of the “Sphex,” a species of wasp that paralyses caterpillars to lay their eggs in them. Thematism, for Bergson, defines a profound notion of the functioning of instinct and presents itself as a real and non-mechanical point in front of which the different variations of behavior are executed. With the theory of theme and variation, Bergson proposes, as we know, an interpretation by sympathy, taking “wasp and caterpillar” as two activities. By taking up Bergson’s thesis, Ruyer considers that animal behavior is therefore not a precisely and blindly chained mechanism; instinct is creation and guidance in relation to themes that “fly over” the activities. Ruyer’s article has the merit of examining the notion of instinct as knowledge and discus the references used by Bergson. Defending Bergson against the accusations of using the Sphex case, Ruyer develops important considerations on the theory of instinct and thematism and, considering the problems dear to Bergsonism, he especially pays homage to the philosopher of creative evolution.