70 BIRD FRIENDS 



other means of controlling these pests. If to this 

 be added the loss in sickness and death caused by 

 mosquitoes and flies, the total annual toll that in- 

 sects collect from man in the United States is about 

 one billion dollars. 



Power of reproduction of insects. Insects exist in 

 enormous numbers and have a most remarkable 

 power of increase. It is estimated that if the hop- 

 vine aphis should multiply unchecked and each in- 

 sect should live and find enough food, at the end of 

 one season the number of the last brood would be 

 10,000,000,000,000,000,000,000. Dr. Hodge has es- 

 timated for the mosquito that if each insect should 

 live, and the female lay the average number of eggs, 

 the number of descendants of a single mosquito at 

 the end of six months would be represented by the 

 figure 2, followed by 39 ciphers. Of course this can 

 never happen, on account of abundance of its ene- 

 mies and lack of food. • 



Amount of food eaten by insects. Another fact 

 that makes insects so destructive is the enormous 

 amount of food they devour in a short time. Many 

 caterpillars eat each day twice their own weight of 

 leaves. Sometimes a single day's work of an army 

 of insects may be enough to destroy a crop. 



Nature's check on insects. The wonderful power 

 of reproduction possessed by insects and the enor- 

 mous amounts of food eaten suggest how important 

 it is that there should be checks constantly at work 



