Generalist carabid beetles are more malacophagous than previously recognized and cause diversified types of shell damage

Abstract

Although most carabids are carnivorous generalists, some species show dietary specializations such as malacophagy, which is characterized by two main strategies of snail predation: entering the shell or breaking it. The shell-breaking strategy has been well studied in the malacophagous specialists of the tribe Licinini. However, little is known about the ability of other carabids to feed on snails and, in particular, to use the shell-breaking strategy. Therefore, the main objective of this study was to investigate the ability of various generalist carabid species to feed on snails under laboratory conditions. We recorded 723 instances of predation in 89 of 180 carabid individuals (representing 23 of 33 species); all of them were exclusively shell-breaking attacks. While carabids mostly favoured individuals <8 mm as prey, they showed no preference for shell shape. Using a subset of 14 carabid species with a high frequency of snail predation, we found significant differences between the predation rates of carabid species depending on their body size using GLMMs. This study revealed that many generalist carabids can indeed feed on snails by breaking the shell, but predation rates were highly inconsistent among individual species. Shell-breaking patterns of generalists differed markedly from those of malacophagous specialists reported in the literature, as damage parallel to the shell coiling axis occurred more frequently than spiral damage. Our results show that the shell-breaking predation patterns of carabids are closely related to their degree of dietary specialization on snails and that many generalist carabids frequently accept snails as their prey.