10 



BIOLOGY AND HUMAN LIFE 



army of locusts travels across a state and destroys every bit of 

 grass and foliage in its path. Some of these activities are slow 

 or not easily observed. Thus, the coral animals, in the course 

 of centuries, build up an island in the midst of the sea ; a grow- 

 ing tree splits a great rock asunder with its expanding roots. 



Some plants and animals produce effects that do not last long 

 or reach very far, but others produce effects that reach down 

 through long periods of time or spread over wide regions. For 



Fig. 4. The shipworm, or teredo 



This animal does a vast amount of injury to piers and wharves by boring into timbers 

 that are kept in salt water. The teredo is not a worm but a relative of the clam. 

 The one in the picture was nearly 20 inches long and made a hole about ^/i inch in 

 diameter. Hundreds of thousands of holes cut into a log in all directions will soon 

 ruin it. (Courtesy of National Research Council) 



example, the teredo worm (which is not a worm at all, but a 

 kind of clam) honeycombs the timbers of a harbor so that at 

 last a large wharf crashes down (see Fig. 4) ; or a slowly grow- 

 ing forest gradually changes the stream flow or even the whole 

 weather condition of a large and remote area. 



Some of these changes produced by plants and animals are 

 interesting to us because of their unusualness or their dramatic 

 qualities. Others are of importance to us because they influ- 

 ence our own lives for better or for worse. ]Moreover, what is 



