POISONOUS SNAKES OF NORTH AMERICA, 481 



EXTERMINATION OF POISONOUS SNAKES. 



It can be stated as a general rule that our poisonous snakes are 

 decreasing rapidly in numbers, and that consequently the danger from 

 their bites is constantly diminishing. In many localities where rattle- 

 snakes were formerly numerous they have now become entirely exter- 

 minated, while in others they are extremely rare. The causes that 

 liave led to this are various, but the commonest cause is undoubtedly 

 the increasing cultivation of the country. In other places the decrease 

 in the number of the snakes can be traced directly to their being killed 

 off by the hog, an animal certainly not proof against the venom if it 

 enters the circulation, but usually well protected by its fat, which is in 

 most cases sufficiently thick to prevent the fangs of the serpent from 

 penetrating to the nnderlying tissues. 



From other localities there is reported a similar decrease without it 

 having been possible to offer a satisfactory explanation. As a striking 

 illustration of this, I may cite the experience of an exploring party 

 under Dr. C. Hart ]Merriam, camping for several months at the base of 

 the San Francisco Mountain, Arizona, in 1889. The party consisted of 

 a number of naturalists, specialists in mammalogy, ornithology, herpe- 

 tology, and botany, who were busily engaged in studying the fauna 

 and tlora of that mountain for several months during the summer. Yet 

 not a single rattlesnake was collected or seen by the party in that 

 locality where twenty-five years previously Dr. E. Cones had collected 

 quite a series of them, belonging to several species, during a compara- 

 tively short stay, notwithstanding the fact that the character of the 

 country has apparently not changed in any essential particular. It 

 has not been brought under cultivation; there are no hogs running 

 about, only herds of cattle 5 no regular burning over of the ground 

 takes place; no special enemies could be discovered; a few people pass 

 occasionally through the district, and fewer still live there permanently. 



On the other hand, there are instances on record of localities in which 

 certain species of poisonous snakes have actually increased. This may 

 occur in places, for instance, where the land was formerly burned over 

 regularly everj^ year, thus destroying the snakes in great numbers. 

 Dr. H. H. Behr* attributes the increase in the number of rattlesnakes 

 in some localities not far from San Francisco to the killing off of the 

 enemies of the snake, notably birds of prey and other snakes, and 

 probably correctly, while Mr. Hurter (Trans. Acad. St. Louis, vi, 1893, 

 11. 258) reports a similar increase in western Illinois as due to the new 

 stock law compelling swine to be penned up. 



The poisonous snakes have a great many natural enemies which keep 

 them in check, but there does not seem to exist in this country any 

 animal which makes a specialty of the business and is particularly 



' Proc. Calif., Acad. Sci. (2), i, 1888. pp. 94-99. 

 H. Mis. 184, pt. 2 31 



