SNAKES, LIZARDS, TURTLES, AND CROCODILES 269 



ground squirrels or other pests. The blind snakes, genus 

 Glaucoma, burrow in the earth and feed on insect larva and 

 worms. 



Among the most familiar of the many non-poisonous snakes 

 are the striped garter-snakes, genus Thamnophis, found every- 

 where in the fields and gardens. The common water-snake, 

 genus Natrix, is only semi-aquatic, spending most of the time 

 on land in the vicinity of ponds or streams. They are ex- 

 cellent swimmers and quickly take to the water when alarmed. 

 The large blacksnake, Zamenis constrictor, and the blue-racer, 



FIG. 123. A king-snake, Lampropeltis boyli. (After Snyder.) 



which is merely a color variety of the same species, are common 

 in open meadows, where they feed on frogs, mice, eggs, young 

 birds and other animals which they swallow alive. The 

 king-snakes, genus Ophibolus, are so called because they feed 

 on other snakes. They seem to be immune to the venom of the 

 poisonous snakes and readily attack any of them. The puff- 

 adders, or spreading vipers, or blow-snakes, genus Heterodon, 

 are commonly supposed to be poisonous but are really quite 

 harmless. No American snake with slender, sub-parallel- 

 sided head is poisonous. 



The dreaded rattlesnakes, and the copperheads and water- 

 moccasins, are thick-bodied venomous snakes with flat, tri- 

 angular heads and with strong tubular fangs which are folded 

 flat against the roof of the mouth when it is closed. When 



