Polymorphism in the snake Psammophis schokari on both sides of the desert edge in Israel and Sinai

The snake Psammophis schokari (Colubridae) occurs in Israel and Sinai, Egypt, in three pholidotically indistinguishable morphs: (1) striped, with four dark longitudinal stripes; (2) non-striped, plain or lightly dotted; and (3) rear-striped, dark stripes on the posterior part merge anteriorly (this pattern is first described herein). From 100 museum specimens it appears that the striped snakes occur mainly in the northern mesic parts of Israel, the non-striped mainly in the southern deserts, and the rear-striped mainly in a central belt. The distributions are correlated to rainfall, solar radiation and vegetation. This polymorphism may be maintained by crypsis, thermoregulation or both.