I2O LIVING CREATURES. 



PART 2. 



FLIES have each but one pair of wings, and include 

 gnats, mosquitoes, horse-flies, blue-bottle flies, and a 

 host of others. The "blue-bottle" is larger than the 

 house-fly, and is regarded as a pest and an enemy to the 

 housekeeper and the butcher. Blue-bottle flies are at- 

 tracted by the smell of meat, and manage to deposit 

 their eggs upon this food, though it be covered with 

 wire netting or with cloth. The eggs hatch in about 

 twenty-four hours, and the larvae are the maggots which 

 are so detestable. However, this vexatious visitor does 

 a great deal of good by helping to get rid of decaying 

 animal matter. 



How wonderful is the increase of flies ! Mr. Keller, 

 an English naturalist, has calculated that the early fly 

 lays eighty eggs at each of four times during the sea- 

 son. The first generation after her lay four times ; the 

 second three times, the third once; and the offspring 

 of these again deposit eggs, so that, should all the 

 eggs hatch and produce flies, the original fly would be 

 the parent and grand parent of two millions of chil- 

 dren. Enemies and accidents must remove a great 

 many of the eggs or of the young flies. 



Many insects seek to deposit their eggs upon the. 

 substance that furnishes the proper food for the larvae 

 which are hatched from their eggs. For this reason 

 the blue-bottle fly searches for meat ; the potato-beetle 

 finds the potato plant ; and the moth of the tomato- 

 worm deposits upon the tomato or the potato vine. 

 Sometimes a mistake is made. A meat-eating insect 



