man's place in the web of life 47 



the direct relationships, but they are so exceedingly complex 

 that they can only be mentioned here. 



There is one phase of the subject, however, that must be 

 noticed. Man has often tried to assist nature for his own 

 benefit with sometimes unforseen and more or less disastrous 

 results. The mongoose was introduced into the West Indies 

 to kill the rats, which were a serious problem in the cane fields. 

 First a large gray mongoose was brought in which did not 

 thrive, and later a small brown one which throve too well. 

 The most noticeable result of this introduction of the mon- 

 goose was not a diminution in the numbers of the rats, but 

 a marked decrease in the numbers of the small doves and 

 other ground nesting birds and of the lizards, coupled with a 

 great increase in the numbers of obnoxious insects. For 

 instance on St. Lucia the screw-worm flies soon became abun- 

 dant and a terrible pest to live stock. Why? Because these 

 flies, which Hke to sun themselves on rocks and fence rails, 

 fall an easy prey to the numerous small lizards which frequent 

 just such situations, and the mongoose feeds largely upon 

 these little lizards. 



On the adjacent island of St. Vincent, fifteen miles away, 

 two sorts of mole crickets promptly increased enormously. 

 Mole crickets on St. Vincent are eaten by a large ground 

 lizard which, noting the surface movements which they cause, 

 runs to the spot and digs them up. The mongoose found the 

 young of these ground lizards easy prey, resulting in the great 

 increase in the mole crickets. But the increase in the mole 

 crickets had been noticed by the local chicken hawk which 

 previously had fed upon small lizards chiefly; and in 1903 

 I found these hawks to be the main consumers of the mole 

 crickets. 



The history of the introduction of rabbits into Australia, 

 of the gypsy moth and brown-tail into New England, and of 

 hosts of other cases, show the delicacy of the animal balance 

 in the world in which we live and the complexity of man's 

 contacts with it. 



