INSECTS BENEFICIAL AND BEAUTIFUL 



253 



The tachina flies are another numerous family of 

 extremely beneficial insects. They are large to medium- 

 sized flies and resemble the house fly in form and general 

 appearance. They are the stout, bristly flies that we see 

 so often on sunny days about rank vegetation. Their 

 larvae are all parasitic on other insects, chiefly on the 

 injurious leaf-eating caterpillars. While an ichneumon 

 commonly attacks only a single species or its near rela- 

 tions, the tachina flies present the advantage of working 

 upon almost any in- 

 sect that may be 

 numerous. Thus a 

 tachina fly will lay 

 her eggs on a cater- 

 pillar, if she can find 

 one. If not, she 

 may lay them on 

 grasshoppers, bugs, 

 beetles, sawflies, or 

 even bumblebees. 



The white, oval eggs are glued to the body of an insect as 

 though they were a part of its own skin. The little maggots 

 on hatching burrow into their victim and feed upon its tis- 

 sues and juices. Growth is rapid and after its attainment the 

 little plunderers are said to murder their host by destroying 

 a vital organ, after which they work their way out. Unlike 

 the ichneumons the tachina larvae spin no cocoons, but 

 instead the outer skin hardens into an oval case, the pupa 

 case, or puparium ; within this the larvae change into pupae, 

 and in about ten days we may expect to see them emerge 

 as adult flies. There may be several generations a year. 



FIG. 107. TACHINA FLY 



Eggs on a caterpillar, larva, adult, and pupa ; size 

 a little larger than a house fly 



