In the final stages of an elaborate courtship, many slugs and snails shoot 'love' darts into each other. While darts improve the reproductive success of the shooter, it is unclear why some species have darts and others do not. In fact, dart use has barely been studied except in the garden snail Cantareus aspersus (Helix aspersa). We therefore took an evolutionary approach to attempt to understand the use of darts, by investigating mating behaviour in a range of species. The prediction was that, because darts could have arisen out of an escalating cycle of sperm digestion and investment in sperm, then darts should be found in taxa that enforce simultaneous reciprocity during mating. Mating behaviour in 60 genera of land snails and slugs was recorded, and compared against dart use and a phylogeny. 'Face-to-face' simultaneous reciprocal-mating behaviour is restricted to three monophyletic groups of snails and slugs, and dart-bearing species are a subset within the same clades, which suggests a link, though not necessarily a causal one. As yet, we are unable to quantify the extent to which darts or mating behaviour are determined by common ancestry or regimes of natural or sexual selection, because the current phylogeny lacks resolution. However, the results emphasise that to understand the use of darts, then data are required from a wide range of species. The realisation that several characters are correlated may stimulate further research, and could eventually lead to some testable models for dart and mating behaviour evolution.