12 ZOOLOGY 



the (>nerg}' of the sun, but only indirectly by feeding on vegeta- 

 tion. Now the group of animals that ranks first among the 

 feeders on terrestrial vegetation is that of insects. 



Geolog}^ tells us that land plants first liecame prominent in 

 what is called the Devonian age, or the age of fishes. At this 

 time ferns and allied small plants and cone-bearing trees were 

 already abundant. At this same time the first insects appeared, 

 and some of them were like our crickets and grasshoppers. In 

 the next age — the Carboniferous — vegetation developed enor- 

 mously, and it was at this time that most of our great coal-beds 

 were laid down by the death of great forests. Insects appeared 

 in great abundance and variety and most of the lower groups 

 of insects that we now know were there. So we see that the 

 development of insect life on the land went on hand in hand 

 with that of vegetation. 



That insects have played well their part as devourers of 

 vegetation there can be no doubt. We shall have occasion 

 to see that tliis is so as we consider one l^y one the different 

 groups of insects. One has only to consider the constant fight 

 that the farmer wages against the insect enemies of crops to 

 realize how fully able insects are to destroy vegetation. Every- 

 where the farmer uses poisonous sprays or powders, and even 

 then his losses b^' bugs, cotton-boll beetles, potato-beetles, 

 scale-insects, and the rest amount to manj' miUions of dollars 

 each year. As an example of destructive insects none is better 

 than the grasshopper. 



The grasshopper is, like the cricket, an animal belonging 

 to a group known as insects (technically Hexapoda'). The 

 group is given this technical name because nearly all insects 

 have six legs. With few exceptions insects have also both 



' From two Greek words meaning " aix " and " legs." 



