Using museum collections to explore predator–prey relationships in snail-eating beetles (Carabidae: Cychrini)

The vast majority of species interactions in nature go unnoticed because they occur under circumstances unamenable to observation. This is unfortunate, as our understanding of trophic ecology is predicated on our ability to quantify the nature and magnitude of species interactions. Here, we use specimens from museums and private collections to estimate prey breadth and morphological patterns between predator and prey pairs of the malacophagous Cychrini beetles collected alongside their snail prey. We identified each pair, measured a series of morphological traits on each, and tested for relationships between the morphological characteristics of beetles and the snails they were found eating. Of 38 specimen pairs, we identified 12 species of Cychrini beetles from two genera (Scaphinotus and Cychrus) eating 22 species of snail prey from 12 genera and ranging from 1 to 9 species of snail prey per beetle species. We found 29 unique predator–prey species pairs. Irrespective of species identity, we found that female beetles were discovered eating larger snails compared to male beetles. We detected two trends in which larger beetles were found eating snails with relatively larger aperture openings, and beetles with more slender body shapes (longer, thinner mandibles, heads, and pronota) were found eating snails whose shells had relatively smaller aperture openings. This suggests that, even within the carabid tribe Cychrini, variation in the cychrine body form may influence prey availability. This study provides the most comprehensive list to date of predator–prey pairs in this understudied group of beetles and also demonstrates the utility of museum collections for documenting cryptic species interactions.