The role of venom in the hunting and hoarding of prey differing in body size by the Eurasian water shrew, Neomys fodiens

Abstract

Being venomous should help a predator to maximize foraging gain, reduce handling time, and hoard food. Shrews are a good model for study of the relationship between venomousness and optimal foraging as they have to be highly efficient foragers (because of extremely high energy requirements) and comprise a few venomous species. We hypothesized that venom facilitates shrews to overpower large prey and enables hoarding of (mainly large) prey in a comatose state. We compared hunting and hoarding behaviors of the venomous Neomys fodiens and the nonvenomous Sorex araneus, which were allowed to forage on live prey differing in body size. As we predicted, small invertebrates were immediately consumed by both shrew species, whereas larger ones were immobilized and hoarded. Smaller S. araneus hoarded proportionally more food than larger N. fodiens. Although different ways of prey immobilization were expected (venomous paralyzing by N. fodiens and mechanical damage by S. araneus), both species seemed to use mechanical immobilization. However, N. fodiens required significantly less time than S. araneus to subdue prey of proportionally similar sizes and this difference grew with the increase in prey mass. Only N. fodiens was able to overpower and kill frogs (but not larger toads). We concluded that the relatively weak venom of N. fodiens is helpful in overpowering and hoarding mainly medium-sized prey. Thus, venomousness helps N. fodiens to optimize its foraging as it reduces prey handling time, enables it to gain larger energy portions, and facilitates food hoarding, which reduces foraging time.