AMPHIBIA AND REPTILIA OF COLORADO 4I 



because it varies, within certain limits, as the temperature of the 

 surrounding medium — water or air — varies. They can withstand con- 

 siderable fluctuation in blood temperature without fatal consequences. 

 Nevertheless, such changes have a marked influence upon the activity 

 of these lower vertebrates, especially the reptiles. They are sluggish 

 during cool weather and active during warm weather. Though large 

 portions of Colorado never suffer from extreme cold, and the direct 

 rays of the summer sun are often quite hot at midday over a consider- 

 able part of the state, yet on the whole the climate is cool, and even 

 in the warmer areas the diurnal changes are great. The climate of 

 the mountains, which occupy so much of the state, is especially cool, 

 and above the 9,000-foot contour frost is apt to occur every month in 

 the year. Hence a portion of the state is wholly unadapted to rep- 

 tiles, much of it unfavorable, and little of it especially favorable. 

 Lizards, which are so well represented, both in species and in indi- 

 viduals, in the states to the south and southwest, are represented by 

 fewer species in Colorado and entirely unknown in large areas, though 

 the small swifts and horned lizards are rather abundant in favorable 

 localities. Aridity seems favorable to lizards, but most species of 

 reptiles and amphibians are confined to the vicinity of perennial 

 streams, ponds, marshes and lakes. A large portion of Colorado being 

 semi-arid, this is another limiting factor, though some species of snakes, 

 such as the prairie rattlesnake and hog-nosed snake, are common on 

 the dry plains. In some portions of the world forests harbor many 

 reptiles and amphibians, but the forest areas of Colorado are confined 

 to the mountains and high mesas, which are otherwise unfavorable to 

 a large reptilian and amphibian fauna. 



Poisonous Species. — There is a widespread fear of snakes, lizards 

 and salamanders, which is often said to be instinctive. It may well 

 be doubted whether this fear is really instinctive. In many com- 

 munities children are purposely taught to fear these animals, because 

 some species are dangerous and they are unable to discriminate. In 

 other instances children imbibe their fear from others, in the absence of 

 conscious effort to teach them. Such fear, instilled into the minds of 

 children, is very difficult to eradicate in later years. An astonishing 



