CHAPTER XV 

 The Two-winged Parasites 



IN the great order of two-winged flies (Diptera) there 

 are many parasites of other insects. A large proportion of 

 these belong to the family of Tachina Flies (Tachini- 

 dae). These are mostly insects of moderate size, similar 

 in appearance to the common house fly but usually some- 

 what larger. 



These Tachina parasites have long been recognized as 

 among the most important enemies of such smooth-skinned 



caterpillars as cutworms 

 and army worms, often 

 destroying millions of 



these pests at the time 

 of a single outbreak. 

 TACHINID of ARMY-WORM The life history as shown 



by the species that in- 

 fests the army worm is briefly this : The adult flies de- 

 posit their oval whitish eggs upon the outside of the skin 

 of the caterpillar. These eggs shortly hatch into tiny 

 larvae by burrowing through the eggshell and also through 

 the skin of the caterpillar, finding lodgment among the 

 body tissues. Here they rapidly develop into whitish foot- 

 less maggots that finally kill the host and emerge to change 

 to the pupa state at or near the surface of the soil. They 

 soon again change to adult flies to continue the generation 

 of the parasite. 



188 



