30 INTERRELATIONS OF PLANTS AND ANIMALS 



This life history gives us an example of what is known as a 

 complete metamor' yJiosis or change of form. 



Plants furnish Insects with Food. — The insects which we have 

 seen on our field trip feed on the green plants among which they 

 live. Each insect has its own favorite food plant or plants, and in 

 many cases the eggs are laid on the plant so that the young may 

 have food close at hand. Some insects prefer the rotted wood of 

 trees. An American zoologist, Packard, has listed 462 species of 

 insects that live upon oak trees alone. Everyivhere animals are 



engaged in taking their 

 nourishment from plants, 

 and millions of dollars 

 of damage is done every 

 year to gardens, fruits, 

 and cereal crops by in- 

 sects. 



All Animals depend on 

 Green Plants. — ^ Insects 

 in their turn are the food 

 of birds ; cats and dogs 

 may kill birds ; lions and 

 tigers live on large de- 

 fenseless animals such as 

 deer or cattle. And 

 finally, man eats the 

 bodies of both plants 

 and animals. But if we 

 reduce this search for 

 food to its final limit, we see that green plants provide all the food 

 for animals. For the lion or tiger eats the deer which feeds upon 

 grass or green shoots of young trees, and the cat eats the bird that 

 lives on weed seeds or on insects that eat plants. Green plants 

 supply the food of the world. 



Homes and Shelter. — On a field trip no one can fail to observe 

 that plants often give animals a home. The grass shelters grass- 

 hoppers and smaller insects which can be obtained by sweeping 

 through the grass with an insect net. Some insects, such as the 

 tent caterpillar, build their homes in the trees or bushes on which 



Trees with leaves destroyed by insects, in the 

 Yosemite Valley, California. 



