Is the Slow Worm a Batesian Mimic?

Abstract

THE phenomenon of Batesian mimicry, where an edible animal gains an advantage by mimicking a distasteful or dangerous animal showing a warning pattern, is well known and has been described by many authors^1–4. The advantage gained by a mimic decreases if the mimetic form becomes too common, since a predator may learn that the warning signal mimicked is a sign of edibility rather than danger; thus selection for the mimic is density-dependent which, as shown by Haldane and Jayakar⁵, will often lead to a balanced polymorphism where both mimetic and non-mimetic forms are retained in the population. Matessi and Cori⁶ suggest that mimetic inheritance is often sex-limited so that the expression of mimicry is limited to one sex (usually the female according to Sheppard³) although individuals of the other sex may have the mimetic genotype. It is suggested here that the slow worm (Anguis fragilis L.) has a form of colouration exhibited by the young and some adult females which is a mimic of the warning pattern of the adder (Vipera berus L.).