Freshwater gastropods often contribute significantly to freshwater ecosystem biomass and are a vital component of many consumers' diets. They can also serve as a nutrient resource for terrestrial predators, representing an important example of nutrient transfer across a habitat boundary. This study uses bankside middens to provide evidence of predation by the brown rat Rattus norvegicus on the native freshwater gastropod Viviparus viviparus in a closed, lentic system in Ely, southeastern England. Conchological analysis of shell remains in middens compared with live snails in adjacent water sites suggested this predation could be size-selective for larger snails, and analysis of soft tissue dry weights and the mechanical force required to break shells suggested that this was driven predominantly by maximizing nutrient gain, rather than by optimizing handling effort. Aquatic gastropods represent a potentially important nutrient resource for brown rat populations; this resource may be used continuously through time or exhibit ‘resource pulse’ dynamics. Predation of this nature might also have important impacts on gastropod population structure, which may in turn impair ecosystem functioning.