INSECTS 57 



43. Habits and life history of the house fly. It has 

 been clearly proved that the common house fly is a fre- 

 quent cause of disease; especially is this true in the trans- 

 mission of typhoid fever and the intestinal diseases to which 

 the deaths of so many young children are due. Practically 

 all parts of the body of a fly are covered with hairs (Fig. 41), 

 especially the mouth parts and feet. Each foot, also, has 

 sticky pads (Fig. 40) which enable the fly to cling to the walls 

 and ceilings. In the adult stage the flies feed upon filth 

 of all sorts, and if they alight on the excretions of typhoid 

 patients, they are very likely to carry on their feet and 

 mouth parts the germs of the disease, and 



so when they come into the house, they 

 may infect milk and other food. Flies 

 also carry germs of other diseases such as 

 cholera, dysentery, and tuberculosis. 



The most common breeding place of FIG. 40. Foot of fly, 

 house flies is in piles of horse manure. ^ ing hairs and 

 Here the female fly lays about 120 eggs 

 (Fig. 41) which hatch within a few hours into tiny white 

 footless grubs. These feed for about five days upon the 

 manure and grow rapidly, molting twice within that time. 

 The larva now changes into a pupa, and at the end of another 

 five days the adult fly emerges from the brown pupa case. 

 Egg laying begins almost at once, and as each adult female 

 fly lays 120 eggs, it has been estimated that a single fly may 

 have 5,598,720,000 descendants in a single season if each fly 

 were to deposit but one batch of eggs. In reality, however, 

 a fly deposits four batches in a season. Hence it is very impor- 

 tant to catch and kill flies at the very beginning of each season. 



44. Extermination of house fly. Because of the danger 

 of disease transmission every housekeeper should do her best 



