236 



THE RISE OF ANIMAL LIFE 



Fig. 11-30. The rat flea, carrier of bubonic plague. 



food for bees, von Frisch discovered that 

 the circling dance meant that the source 

 was less than 100 meters away, whereas the 

 wagging dance meant that it was beyond 

 that distance. Direction is determined by 

 the position of the sun. If a bee is caught 

 and then released very soon, it finds its way 

 home without any difficulty. If, however, it 

 is caught and placed in a dark box for two 

 hours and then released, it will fly along the 

 path that it would have taken when the sun 

 was in the position it had been two hours 

 earlier. Thus the bee is able to measure the 

 angle of the sun and use it as a guide in 

 returning home. It is able to do this even 

 on cloudy days or when it sees only a small 

 portion of the sky. Hence this little animal 

 seems to possess powers of response never 

 dreamed of in lower animals. Perhaps there 

 are many more, equally as extraordinary, 

 awaiting our discovery. 



Insects unlimited 



Insects are so widespread and numerous 

 and touch upon man's life in so many ways 

 that no one is entirely free from their influ- 



ence, from the housewife who fights the 

 ubiquitous fly and cockroach to the flea- 

 and louse-bitten beggar who is constantly 

 struggling to rid himself of these pests. On 

 the other hand, there are those who operate 

 a million dollar industry and profit by the 

 labors of the honeybee or the silkworm. 

 Moreover, there are vast fertile areas of tlie 

 globe that are denied occupancy by man 

 because of the presence of insects which 

 carry deadly diseases. The competition that 

 is going on between man and these tiny 

 beasts is quiet and not too apparent to 

 the ordinary person, but it is a deadly battle 

 and it is not at all certain that man will al- 

 ways be the victor as he is today. He might 

 better employ his efforts to fight this enemy, 

 rather than to fight his fellow man. 



Perhaps the most benefit derived from 

 insects is from their work as pollinators of 

 flowers. Many trees would bear no fruit if 

 it were not for various insects, and the same 

 is true of such crops as clover and figs. Shel- 

 lac is made from a secretion produced by 

 certain lac insects in India; others produce 

 a dye called cochineal. The cocoon of the 

 silkworm is unwound and spun into silk 

 thread used to make the fine silk cloth fa- 

 miliar to everyone. 



On the debit side are those insects which 

 carry disease, such as the mosquito (ma- 

 laria, yellow fever, filariasis), the body 

 louse (typhus), and the flea (Fig. 11-30) 

 (bubonic plague). In the past and still to- 

 day these diseases are the cause of a vast 

 amount of human misery. Bubonic plague 

 alone wiped out from one-half to three- 

 fourths of the population in vast areas of 

 the world several centuries ago. Today ap- 

 proximately one-sixth of the population of 

 the world is made wretched by malaria. 

 With the eradication of the mosquito alone, 

 much suffering would cease. 



Domestic animals also are harassed 

 throughout their lives by numerous insects. 

 The botfly causes most serious damage to 

 the stomachs of horses, while the ox warble 

 fly larvae bore holes in the hides of cattle 



