DIPTERA 



47 



fly, which lays its oval white eggs on decaying meat, 

 where the larvae (maggots) complete their growth in about 

 ten days; the screw-worm fly, usually breeding in putre- 

 fying flesh, but sometimes in sores on animals and even 

 human beings; and the cabbage fly, whose maggot lives in 

 the roots of young cabbage and cauliflower in early sum- 

 mer, causing great loss to these crops. 



Other Important Flies 



Tachina Flies. All of the numerous species of the 

 Tachinas are beneficial, as their larvae feed on the larvae 

 of harmful insects such as caterpillars 

 and cutworms. The surest way to 

 secure specimens is to look for the 

 minute oval eggs glued to the skin of 

 a caterpillar, which should be fed in 

 a box containing an inch or two of 



,-, mi- ilAr FlG - 25. Photograph of 



earth. The little maggot emerging a Tachina fly. Twice 



from the lower side of each egg 



penetrates the host and feeds on its fatty matter a week 



FIG. 26. Photograph of four eggs of a Tachina on a larva of a Catalpa moth. 

 Natural size. 



or two, after which it comes forth and remains several days 

 on or near the surface of the ground, a quiescent pupa 



