FAMILY T AC HI N I DM 275 



special reference to its mode of introduction is believed to 

 follow the same method, but Miss Ormerod persisted in the 

 belief that the eggs were deposited on the back and that the 

 larvffi bored through the skin, and claims to have seen chan- 

 nels through the skin througli which the lar\-ie tra\'elled. It 

 is not likely that there would be this difference in the two 

 species. This species causes a great deal of loss in the old 

 world. The one method available for controlling either of 

 these species is the destruction of larva? during the late 

 winter and early spring when they are conspicuous along 

 the back, and the method of extermination of the species 

 would be to have all animals examined and all the grubs found 

 destroyed. This is feasible theoretically, but impossible 

 practically. They do not migrate far, and any stock owner 

 can by close attention secure a large measure of immunity 

 for his own herd. Cooperation would secure a more extended 

 extermination. 



Sheep Bot Fly {Oestrus ovis). — The sheep bot fly illustrates 

 another method of development. It deposits eggs or newly 

 hatched larvae in the nostrils of sheep and these work their 

 way up the passages. This entrance occurs during summer 

 time and the development of the larvse goes on through fall 

 and the larvae work their way back in spring and pupate in 

 the ground and the flies issue in midsummer. They cause 

 the greatest irritation and most serious symptoms occur 

 during the time the larvae are working themselves back. 

 The sheep sneeze, etc., and sometimes show a dizziness or 

 stagger. They may be cut out of the frontal sinuses but the 

 cost of the operation is too great for general use. Preven- 

 tion consists in avoiding the deposition of eggs in the nos- 

 trils, x^pplying tar to the noses is one method, and another 

 method is by furnishing plowed places or dusty places so that 

 the sheep can bm-y their noses when the flies try to deposit 

 eggs, or by giving the sheep a shed, as the flies are active 

 in the sun and not in the shade. 



Family Tachinidse. — The family Tachinidce has a very 

 important economic position on account of the large number 

 of species that are parasitic upon destructive insects. The 



