ENTOMOLOGY 21 



reduced them to their normal numbers. In a state of nature plants 

 distribute themselves in such a manner that one kind never occupies 

 the ground exclusively. Our native foreste are not composed of one 

 species of trees, but of very many kinds, in constantly varying pro- 

 portions which depend upon the character of the soil and the needs 

 of the different kinds of trees. The same is true of the plants that 

 clothe our beautiful prairies. Notwithstanding the uniformity of 

 the soil the prairies are covered here and there with different plants. 

 Animals, and chiefly insects, depending directly or indirectly upon 

 plants, naturally follow their distribution. When the sod of our 

 prairies was broken to receive the seeds of plants not grown there be- 

 fore, the soil responded freely to the new demands and yielded phe- 

 nomenal crops. This prospective reward for agricultural toil soon 

 attracted more and more farmers until the prairies were teeming 

 with human beings, eager to mine the golden grains the only form 

 of mining that will make a people really happy and prosperous. But 

 in cultivating more and more soil, man destroyed the finely balanced 

 relation between the animal and vegetable kingdoms by adding a dis- 

 turbing factor. At first but few destructive insects to the new crops 

 were found, because they had to be introduced from elsewhere ; but 

 as soon as they found this Eldorado an immense area covered with 

 the best kind of food for them they were not slow to appropriate 

 to themselves what was not planted for them. Insects of all kinds, 

 but at first mainly injurious ones, will invariably take possession of 

 fields where plants of one kind are grown upon a large scale. Insect 

 foes of such plants will soon find their way to such fields and fix there 

 a new home. In course of time, however, things will change for the 

 better, simply because the foes of such newly introduced species will 

 also make their appearance and wage war upon their old enemies. 

 This is one reason why in the older settled parts of the globe insect 

 outbreaks are less frequent, though they are by no means unknown. 

 The disturbed relationship between plants and animals has there be- 

 come re-established. Moreover a more diversified farming is the rule 

 in older countries, and insects there do not find such an abundance 

 of food as where their food is grown upo^ j v very large scale. 



Imported insects usually become injurious because their natural 

 eneix.ies are left behind in the natural habitat of the pest. 



To enable the reader to recognize his friends and foes amongst 

 insects the following two artificial classifications are given. Both are 

 very simple, and the study of insects, in most cases, requires no mag- 

 nifying glasses. It is best to compare with both classifications any 

 insect to be located, that no errors be made. Both classifications 

 apply only to the adult or winged insects. 



Insects with both a biting and sucking mouth : 



Wings with veins: Hymenoptera. 

 Insects with a biting mouth : 



Upper wings horny: Coleoptera. 



Upper wings like pergament: Orthoptera. 



Upper wings with many veins: Neuroptera. 



