THE DIPT ERA 319 



cattle on almost any part of the body during the late spring or summer 

 months, and the larvae bore through the skin into the connective tissue 

 and then wander through the body in the connective tissues until late fall 

 or winter when they locate along the back, a few inches from the back- 

 bone. Here each makes a hole through the skin through which to escape 

 but remains inside, feeding on the pus and bloody matter produced by its 

 presence there, and the swelling caused by the insect is called a " warble." 

 Finally the maggot, now nearly an inch long (Fig. 337) and grayish-white 

 in color, works its way out through the hole and drops to the ground which 

 it enters for an inch or two, and forms a pupa within a brown puparium 

 from which the adult fly appears from 3 to 6 weeks later, the larval period 

 within the cattle being 9 or 10 months. 



The presence of the maggots of the ox warbles in the cattle is shown 

 by a loss of flesh, reduction of the milk in the case of milch cattle, and by 

 the presence, during late fall and winter, of the sores on the back. 



Control. The chief control method in general use is squeezing out the 

 larvae in the back whenever they are observed there. With a little 

 practice, pressing with the thumbs on the skin at the sides of the opening 

 will result in the expulsion of the maggots. During the egg-laying season, 

 cattle in the field may be protected to a considerable extent by the appli- 

 cation of repellents such as are used to keep off Tabanids. 



Various other bot flies attack different animals. Among them are 

 the Horse Bot Flies (Gastrophilus of several species), the larvae of which 

 live in the stomach of the horse during the fall, winter and spring and the 

 Sheep Bot Fly (CEstrus ovis L.) which in the larval stage inhabits the 

 nasal cavities and frontal sinuses of sheep during the same period. 



Family Trypetidse (The Fruit Flies). Some of these small flies attack 

 various fruits in which their maggots tunnel, ruining the fruits. Others 

 mine the leaves of plants, occur in blossoms or form galls in the stems or 

 roots of plants. Those which live in fruit are of economic importance. 

 Most of the flies belonging here have dark bands, or dark markings 

 enclosing transparent spots on their wings. Two species attack cherries; 

 one feeds in currants and gooseberries; one in the apple, thorn, blueberry 

 and huckleberry, and other species injure citrus fruits. 



The Apple Maggot or Railroad Worm (Rhagoletis pomonella Walsh). This 

 insect is apparently a native of this country and its original food seems to have 

 been the berries of the thorn and possibly the blueberry. It has been found in 

 various parts of Canada and the eastern United States as far south as North 

 Carolina and west to Minnesota, South Dakota and Colorado, but is most serious 

 in the northern and eastern portion of this territory. 



The adult (Fig. 338) is about a fifth of an inch long and has a wing spread of 

 about half an inch. Its body is black with light marks on the upper side of the 

 abdomen, and the wings have heavy dark bands. The flies first appear in the 

 orchards early in July in New England (somewhat earlier farther south) and 



