190 AGRICULTURE FOR COMMON SCHOOLS 



appearance from the worm which it was before. It may be 

 a beetle, a fly, a honey-bee, or a beautiful butterfly. This 

 stage is called the adidt or imago stage. Some insects, like the 

 grasshoppers and the squash-bugs, do not go through these 

 four changes very completely, but in every insect the four 

 stages are more or less clearly marked. Insects usually do 

 the most harm in the second, or larval, stage of their lives. 



There are thousands of kinds of insects. The farmer and 

 fruit-grower is interested in many of them, for some injure his 

 crops, while others are useful to him. We can mention here 

 only a few which must serve as examples for all. 



1. Plant-Lice. — These are to be found on all kinds of 

 plants, more often on trees and bushes. They are usually 

 quite small, greenish-colored, and soft-bodied. They suck 

 the juices of plants. The leaves wrinkle or curl up and hide 

 the lice inside. Plant-lice have a little projection on the back 

 part of their body from which honeydew is exuded. If there 

 are ants around one can see the ant go up to the louse and 

 stroke it on the back with its antennae. The plant-louse gives 

 up a drop of honeydew and the ant eats it. For such accom- 

 modation the ants care for some kinds of plant-lice by taking 

 them into the ground and protecting them over winter. Plant- 

 lice on the roots of corn are placed there by the ants. So if 

 there are many ants running around the plants of corn we may 

 be sure that there will be some lice on the corn roots. Plant- 

 lice usually pass the winter in the egg stage and hatch early 

 in spring, and there are several broods during the summer. 



2. Scale Insects. — ^There are many kinds of these, the 

 worst of which is the San Josd scale. Scale insects are flat 

 and scale-like in appearance and are usually covered with a 

 hard, crust-like covering. They are nearly always found on 



