In this paper we show that the number of grass snake (Natrix natrix L.) specimens deposited in Swedish museum collections has declined in the last eighty years, and that this is correlated with a dramatic national decrease in the number of livestock holdings. These results support the hypothesis that Swedish grass snakes are declining and that this may be linked to a loss of important nesting-environments provided by open manure heaps in small-scale farming. Our study suggests that information obtained from museum databases potentially may be used to explore population trends for snakes and other reptiles.