Millipedes have developed specialized chemical defenses against predators and parasites. Here we investigated the strong repellent odour emitted by two julids from the Caucasus, Syrioiulus continentalis (Attems, 1903) and Pachyiulus krivolutskyi Golovatch, 1977. By NMR and GC–MS, as well as compound synthesis, we identified the major compound in the secretions of both species as 4-ethylhex-1-en-3-one. A second compound was ten...