INSECTS. 117 



picked off by hand and killed, when only a few 

 plants are infested; but the process is very slow 

 and uncertain for a large field. 



SOME OF OUR COMMON INSECT PESTS. HOUSE FLIES. 



The house fly is one of the most common and 

 familiar of all insects, and needs but little descrip- 

 tion. It belongs to the order of two-winged (dip- 

 terous) insects. There are four stages in its 

 life-history egg, larva, pupa, and adult. The 

 larva is a small, worm-like, white maggot, and 

 differs very much in form and habit from the adult. 

 Maggots have mouth parts fitted for eating solid 

 substances, while adult flies have them fitted for 

 sucking liquids. 



Flies breed in filth and in decaying animal and 

 vegetable matter, especially the former, or a mix- 

 ture of both. So the presence and number of flies 

 depend upon the amount of decaying organic mat- 

 ter in a neighborhood governed, of course, by the 

 time of year or by the temperature. They breed in 

 nearly all parts of the world, but do so most abun- 

 dantly in" warm countries. 



After eggs have been laid in filth of any kind, it 

 takes but a few hours for them to hatch. The 

 maggots eat for a few days, molt, or change their 

 skin, twice during the time and then go into the 

 pupa, or resting stage. The pupa stage lasts 

 about five days. So it is less than two weeks from 

 the time that eggs are laid till adults come forth. 



