RELATION TO THE FARMER 251 



is a more local species already abundant and vigorous, 

 that derives a moderate advantage through the re- 

 moval of certain of its natural checks and the greater 

 facilities for getting food. 



We must remember that an injurious insect, as 

 generally understood, is not necessarily one that seriously 

 injures plants, but one that causes notable harm to any 

 plant or part of a plant that man wants for his own use. 

 The farmer looks with equanimity upon weedy plants 

 devoured by slugs or caterpillars, but raises an outcry 

 when his cabbages are much less seriously eaten. Yet 

 any insect feeding on a cruciferous weed is likely at any 

 time to take to cabbage, and so the innoxious species of 

 to-day may become the scourge of to-morrow. 



Among the factors that are changed by the farmer 

 in favor of the insect, none is of greater importance 

 than the elimination of the necessity for seeking a food 

 supply. In nature, plants and shrubs of one kind do not 

 often grow in large numbers or on large areas crowded 

 together by themselves. Insects are therefore com- 

 pelled to seek their food and the difficulty of finding it 

 makes a very important check. The farmer removes 

 that when he plants orchards and fields many acres 

 in extent and puts on the same or similar crops year 

 after year. Clean culture, important as it is in some 

 directions, destroys the shelter of ground beetles, of 

 snakes, toads, lizards, tortoises and similar creatures 

 that feed on species that go underground to pupate, 

 like the plum curculio, or hide just below the surface 

 during the day, like the cut- worms. The war on small 

 rodents is especially favorable to insects, because shrews 

 and mice are great devourers of such things. Culti- 

 vated areas are not sought by birds if they can find 

 other quarters, and some species will simply not go 

 into such places at all, even if they are never disturbed. 



