How do the molluscivorous beetles Carabus granulatus and Phosphuga atrata (Insecta, Coleoptera) deal with sinistral and dextral prey?

Predators of asymmetric prey (such as snails) are often asymmetric themselves or display a predation behaviour that is adapted to the asymmetry of their prey. We studied predation of sinistral and dextral forms of the freshwater snail Lymnaea stagnalis (Linnaeus, 1758) by two snail-feeding beetle species, Phosphuga atrata (Linnaeus, 1758) and Carabus granulatus Linnaeus, 1758. We investigated a possible preference for or more efficient predation of prey items with a certain coiling direction. We found that C. granulatus displayed a preference for dextral snails, as opposed to P. atrata, which did not show any preference. We also looked at the asymmetry of the mandibles. In C. granulatus the left mandible overlay the right one in a higher proportion of specimens (93.7%) than in the non-molluscivorous carabid, Calosoma inquisitor (Linnaeus, 1758) (86.7%), whereas these differences were reversed in P. atrata and the non-molluscivorous silphid Oiceoptoma thoracicum (Linnaeus, 1758) (77.0% and 87.4%, respectively). We discuss our results in the context of differences in feeding behaviour: C. granulatus uses its mandibles to tear the body of the snail as it has withdrawn itself in its shell, whereas P. atrata feeds by pre-digesting the snail.