Rare colour morphs in the slow worm Anguis fragilis in Norway

Abstract

The frequency of melanism in Natrix natrix and Vipera berus is known to be high in the Nordic countries. However, melanism in the slow worm Anguis fragilis has previously never been documented in Norway. Here, for the first time, melanism, amelanism, and erythrism in the slow worm in Norway is documented by photographs. There are several observations of erythristic or partly erythristic slow worms with various degrees of red colour as this depends on the amount of erythrocytes in the skin. This leaves some uncertainty about what could be named an erythristic slow worm based on field observations. We used the software CorelDRAW Graphics Suite for the RGB colour profile at the photographs of the slow worms as an extra support for the assessment of reddish colour. Because the photographs were taken under different light conditions and with different cameras, we could not make a defined threshold value to separate normal coloured brown and grey slow worms from erythristic slow worms using this RGB system. However, the RGB values support our visual observations.