CROP ENEMIES AND FRIENDS 221 



2. Collect some common insects. Watch their changes, and write 

 an account of their life history from your own observation. To catch 

 and keep insects, you need a net and 



a breeding jar. The net may be 



made by fastening a handle to a small 



hoop, and gathering to the hoop a 



cheese-cloth bag two or three feet 



long. The jar should have moist 



sand in the bottom and a cover of 



cheese cloth. Keep the insects in it supplied with fresh food, the 



foliage of the plants on which they are accustomed to feed. 



3. Take two twigs infested with plant lice and two potato vines with 

 beetles on them. Spray one of each with Paris green and dust one of 

 each with lime. What is the effect in each case? 



INSECT FRIENDS 



Helpful and Harmful Insects. After man has done his utmost 

 by cultural methods and poisons, it would be difficult if not im- 

 possible for him to keep the vast insect hosts in check. Fortu- 

 nately, he has helpers in the animal world that do the greater part 

 of the work. Among these are birds and insects. 



It is not possible to make a hard-and-fast line between helpful 

 and harmful insects. Some do good in one way and harm in 

 another; some are friends under certain circumstances and foes 

 under others. 



Many insects are directly valuable on account of their products. 

 The bee yields a palatable food, the silkworm a much-prized cloth- N 

 ing material. 



Insects are necessary to the well-being of many plants, to carry 

 pollen and fertilize flowers. Some insects, even those that are 

 annoying, are useful in destroying dead organic matter, such as 

 decaying flesh and vegetables. Thus they purify the air and the 

 soil, and change waste matter into plant food. 



