From God to devil and back? A historical look at the changing relationship between man and Grass Snake The Grass Snake (Natrix natrix) is the only oviparous reptile species able of maintaining sustainable populations in the far north of Europe (up to 67° N). The species owes its far northern distribution to agriculture, or, to be more specific, to stock breeding which resulted in the production and potting up of dung. Dung heaps appear to be perfect breeding sites for grass snakes and even surpass ‘natural’ reproduction sites in quality. We examined whether there are also historical indications for the importance of dung and dung heaps as crucial elements in the Grass Snake’s life cycle throughout Europe. Moreover, we raised the question whether this hypothesized dependence of the Grass Snake on human culture may have had a reciprocal effect. In other words: did the apparent bond of Grass Snakes to agriculture also have a cultural effect? For this, we conducted an historical research making use of historical sources covering a wide variety of disciplinary fields such as natural history, archaeology, and the history of folklore, alchemy and religion. It became apparent that agriculture has had a clearly positive influence on Grass Snakes since the Neolithic. This positive influence of humans on the species did not only result from physical opportunities offered by humans in the form of dung heaps that were beneficial for reproduction and hibernation, but also from the fact that Grass Snakes were considered to be chtonic deities that were not to be harmed. The conversion of Europe to Christianity, however, marked the turning of the cultural tide for the species. From being a god originally, the grass snake turned into the number one symbol of the Anti-Christ: the basilisk. Pre-Christian as well as Christian superstition regarding Grass Snakes survived well into the 20th century and is possibly still present in some remote parts of Europe. However, with the increasing loss of influence of the Christian belief and superstition in large parts of Europe also the witch hunt for the Grass Snake has by now largely come to an end. Measures in the form of creating artificial reproduction opportunities by means of compost and manure heaps rehabilitate the Grass Snake and reinstate this species’ place in our natural and cultural environment.