Sexual Size Dimorphism (SSD) is the important differences between two sexes in some animals that carry a history of evolutionary and adaptation causes between animals and their relationship in natural habitats. Thirty metric, meristic and ratio characters were examined among 33 specimens of Eirenis collaris from Iran Relevant analyses were employed to identify sexual dimorphism between male and female of this rare species of the genus Eirenis in Iran Five metric and two meristic characters show significant value (P ? 0.05). Length of head and tail length were the differentiated characters more than others between sexes. Size of snakes sexes is variable and relative to characters, namely in some characters males are larger than females and vice versa. Tail length is larger in male and has an advantage for male during coupling and larger size in head length in female may be associated to them utilizing larger prey than males.

Keywords