Besides his work on marine biology which legacy is undisputed, Henri de LacazeDuthiers, as other 19th century zoologists, extended his interests to many fields of natural history. He was generally a keen observer (and very talented illustrator) of the anatomy of complex natural structures. In particular, he initiated studies on insect-induced galls addressed in his article "Recherches pour servir à l'histoire des galles" (Lacaze-Duthiers, 1853) and illustrated his research on the subject by magnificent drawings. The purpose of this essay is to report this lesser-known aspect of the work of H. de Lacaze-Duthiers. Without judging the value of Lacaze-Duthiers' research, we aim at extending the questions he raised at his time, and attempt to provide answers using recent knowledge on insect-induced gall diversity, ecology and physiology. In the process, we stress how the issues raised by Lacaze-Duthiers are connected to more general questions that apply to all biological associations between species (including parasitism). We will see that H. de Lacaze-Duthiers paper not only constitutes a pioneering work on insect galls but also addresses concepts that are still very relevant in current research, in particular on the genesis and development of galls.