The origin and evolution of allelochemical sequestration in tiger moths (Arctiidae) is a complex interplay of larval and adult strategies and phylogenetic history. Using a phylogeny of Arctiidae, we examine the acquisition of secondary compounds from larval host plants and the use of secondary compounds and ultrasound in male courtship displays. We note that two sets of defensive signals (secondary chemicals and ultrasound) have been incorporated independently into arctiid courtship displays. Pyrrolizidine alkaloids are used in larval defence, and transformed into male courtship pheromones in several lineages. Phylogenetic inertia best explains the presence of adult collection and use of PAs in the absence of larval sequestration. Ultrasound, an adult defensive display directed at bats and other predators, has also been incorporated into arctiid mating displays. Sensory exploitation appears to underlie this co-option of defence signals for mating purposes.