March, 1922.] 



The Canadian Field-Naturalist 

 THE RELATION OF WILD LIFE TO AGRICULTURE 



47 



By Norman Criddlb, Trbesbank, Manitoba 



In the old days, before the arrival of the settler, 

 when the country was one vast stretch of unculti- 

 vated land, the wild creatures roamed the plains 

 and woods almost at will. They multiplied or 

 decreased according to the prevailing conditions, 

 such as were brought about by the prevalence of 

 food and the presence or absence of natural 

 enemies. Nature had provided that there should 

 be a balance in all things and, therefore, while 

 certain insects or mammals might increase unduly 

 for a time, they were always eventually reduced 

 by other forms which preyed upon them, or by 

 the meteorological conditions that prevailed. 

 Thus the gophers and mice were keot in check 

 by hawks, owls, weasels and other predatory 

 animals; while the insects were controlled by 

 various parasites in conjunction with a host of 

 birds which found in them a palatable diet. 

 There were no violent changes then, such as is 

 brought about by cultivation, and so the balance 

 which nature had decreed was maintained as it is 

 in all parts where civilized man has not set his 

 foot. 



With the advent of civilization, followed by 

 cultivation, conditions became changed. Animals 

 that had previously roamed the wilds in freedom 

 were unmercifully slaughtered with such a lack 

 of discrimination that the useful frequently 

 suffered even more than the harmful. Hawks 

 and owls were among the first to feel this persecu- 

 tion. A few injurious kinds set the farmer 

 against them all, and, as the useful species were 

 much more numerous than the harmful the 

 effects were soon very striking. Rodents had 

 previously subsisted upon wild plants and had 

 found it difficult, at times, to find sufficient for 

 their wants, but the introduction of farming 

 provided an unlooked-for supply. Immediately 

 vast stores of grain were made available and, 

 consequently, as the food supply was now ample 

 and the natural enemies had been killed off, ro- 

 dents increased at a rate hitherto impossible, 

 with very disastrous results to the farmer. 



But this was by no means all. In addition to 

 the rodents, there was a vast army of native 

 insects, a number of which fed upon wild plants. 

 These had fluctuated from time to time according 

 to the available food supply, but the new condi- 

 tions again upset the balance and, farming having 

 provided abundance of food, the insects began to 

 turn their attention to the new supply and soon 

 became pests of importance. Such are the grass- 



hoppers. Wheat-stem Sawfly and cutworms of 

 today, while others, at present less known, threaten 

 to add to the pests which cultivation has thrust 

 upon us. 



One more important factor must be added to 

 those enumerated above. Among the greatest 

 friends of man are a host of small birds many of 

 which nest upon the ground. These, in times 

 past, fed upon insects and wild seeds, and they 

 were especially important in keeping the former 

 in check. In this case cultivation again changed 

 conditions in favour of man's enemies. The 

 insects were able to breed as readily, or even more 

 so, in cultivated ground, as on the original sod; 

 but this was not so with birds which, with every 

 acre of land broken up, were obliged to seek new 

 breeding grounds. Thus, as man adds to his 

 cultivated acreage he encourages the insect pests 

 by providing more food and additional breeding 

 places, while, at the same time, he forces his bird 

 friends to seek nesting quarters elsewhere. 



Pasturing the land has also done much to 

 destroy bird life, especially around the margins 

 of ponds and lakes. At the same time cropping 

 the grass has encouraged grasshoppers. Indis- 

 criminate setting of fires has done more still, and 

 the burning of woodlands has caused a havoc 

 almost unthinkable. Such is a summary of the 

 changes which have led to our present trouble 

 with insect and rodent pests. Man has provided 

 for them, and man alone can reduce or keep them 

 in check. 



We have hitherto dealt only with native animals 

 but in addition to those are a number which have 

 been introduced from other countries. Some of 

 these, like the House Sparrow, were brought in 

 purposely, others have availed themselves of the 

 channels of commerce. It frequently happens 

 that the imported pests are even more dangerous 

 than the native ones, because the latter have 

 always been with us and their enemies are con- 

 sequently at hand; but this is not so with intro- 

 duced species which have more often left their 

 foes behind. The new pests are, therefore, 

 generally unhampered by enemies and consequent- 

 ly spread with great rapidity. Several of our 

 worst pests are examples of this. The Hessian 

 Fly is one, the Cabbage-worm of our gardens 

 another. The House Mouse and Brown Rat have 

 both been introduced, though in the case of these 

 we have both owls and weasels to aid us in keep- 

 ing them in check. 



