80 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



Self-Testing Exercise 



The hind wings of the flies are for (1). The (2) 



of a fly is a maggot. The beetle has a larval stage called a (3), 



which has (4) pairs of (5). A dragon fly in the larval 



stage is called a (6). Aphids (7) their food and do 



much harm in the (8) 



PROBLEM VI. WHY ARE INSECTS SO NUMEROUS? 



There are over 450,000 different known species of insects, or 

 almost three times as many as all other animals put together. 

 From the standpoint of numbers they are a successful group. 

 Why is this so? Several reasons can be given. Scores, often 

 hundreds, of eggs are laid by a single mother, and sometimes before 

 a month has passed each little female insect that has hatched is 

 ready to lay eggs in its turn. This life cycle may be repeated sev- 

 eral times during a season. They grow rapidly, they are often 

 adapted to use food that other animals will not use, as witness the 



C. Clarke C. Clarke 



The moth clinging to the trunk of an elm tree The yellow crab spider on the yellow center of 



is so similar in coloring to the bark that it is the flower and the white crab spider against the 



not noticeable at a distance. background of white petals are inconspicuous 



as they lie in wait for some visiting insects. 



