182 PRINCIPLES OF FARM PRACTICE 



worthless by the larvae of grain moths. Finally, after coming 

 from the mill, the meal may be made unwholesome by meal 

 worms." Of course, it must be understood that not all of 

 these injuries are likely to occur in any one season or to all 

 the plants, but some of them are certain to occur. 



Why insects are able to cause so much damage to crops. - 

 Insects are generally small and may not be readily noticed ex- 

 cept when they occur in great numbers. One may wonder why 

 such small animals are able to interfere so greatly with farm 

 production. 



There are at least four great facts of insect life that help 

 to answer this question. In the first place, there are many 

 kinds of insects; second, they reproduce very rapidly; third, 

 they grow rapidly; fourth, they are equipped to meet adverse 

 conditions. 



Kinds of insects. The number of kinds of insects ex- 

 ceeds the kinds of all other animals put together. It is esti- 

 mated that fully 400,000 kinds of insects are now known, 

 while perhaps as many more have not been studied and 

 described. In the reference just made to corn twelve kinds 

 are mentioned. According to good authority as many as 

 two hundred different kinds of insects may, at one time or 

 another, attack and injure the corn plant. One hundred and 

 twenty-six kinds of insects are known to injure the apple 

 tree and more than five hundred, the oak tree. 



Rapid reproduction of insects. Not only are there many 

 kinds of insects but many of the same kind. Enormous 

 numbers of our common, destructive insects are produced 

 each year. A little figuring will make clear the great repro- 

 ductive possibilities of insects. If an insect should produce 

 two hundred eggs, and half this number should develop into 

 adults which, in turn, should produce the same number of 



