Shell-breaking predation on gastropods by (Coleoptera, Carabidae) with strikingly asymmetric mandibles.

The adults and larvae of some groups in the coleopteran family Carabidae are known to prey on snails (Mollusca: Gastropoda). Most species of the carabid tribe Licinini are believed to feed on live snails. However, the snail-eating behavior of only a few species has been studied. Whether adults of the licinine genus can prey on live snails was tested by providing 155 live snails of 20 species (eleven terrestrial and nine aquatic species) to adults of Bates, 1873, and observing their behavior under laboratory conditions. Six of the 20 snail species have an operculum that can close the aperture of the shell. Each adult attacked all of the snails provided. successfully preyed on ten terrestrial and six aquatic snail species. These beetles used their strikingly asymmetrical mandibles to break the dextral shells along the dorsal part of the whorls from the outer lip of the aperture towards the apex, allowing subsequent consumption of the soft bodies. However, 41.9% of snails could not be eaten by adults. The rate of predation success by decreased with increasing shell size and thickness of snails. In addition, the presence of an operculum decreased the rate of predation success by . The results show that the shell size, thickness, and operculum of some snail species could play important roles in preventing mandibles from breaking the shells. Therefore, beetles may exert selective pressure on the evolution of defensive shell structures in small-sized snails.