Erythrism in the Eastern Grass Snake, Natrix natrix (Linnaeus, 1758)

 We describe the unusual case of erythrism in the Eastern Grass Snake, Natrix natrix. This colour morph is very rare and has not been reported in the literature before. Despite having observed thousands of N. natrix in the field, we personally detected this morph in only three individuals originating from Slovakia, Romania, and mainland Greece, while photos of a fourth individual from a Greek island were provided to us. In addition, a recent study with a large data set from citizen scientists was unable to produce a single reddish Eastern Grass Snake. Such colouration is likewise uncommon in the western members of Grass Snakes (N. helvetica, N. astreptophora), with two examples provided herein. Because the potential biological importance of erythristic colouration is unclear, we encourage other field herpetologists and naturalists to publish their observations of reddish Grass Snakes in the printed literature.