NATURAL ENEMIES 139 



sites have been known to emerge from a single dead cater- 

 pillar. These little flies are called Chakids by entomologists. 

 There is still another group of four-winged flies, some of 

 which attack the Antiopa Caterpillars. These are much larger 

 than the Chalcid flies and are called Ichneumon Flies. In the 

 case of these only one or two parasites develop in each cater- 

 pillar or chrysalis. 



In addition to these various four-winged flies there are cer- 

 tain two- winged flies, called Tachinid Flies, that develop at 

 the expense of the caterpillars. In Xew Hampshire, during 

 recent years, these appear to have been the most abundant 

 parasites of these insects. An egg is laid on the skin of the 

 caterpillar by a two-winged fly, similar in general appearance 

 to Fig. 51. The contents of this egg shortly develop into a 

 tiny grub that burrows through the egg-shell and the skin 

 of the caterpillar into the inside of the body. Here it remains 

 absorbing the body substance of its host 

 and gradually increasing in size. In a 

 few weeks it becomes fully developed in 

 this grub state. By this time the cater- 

 pillar has become sluggish from the 

 effects of the parasite. If the branch 

 Fig. si. Taciunid fly. upon which it feeds is disturbed the 

 (Redrawn from Scudder.) other ca t er pillars are likely to crawl 

 away, but it remains in its place. The caterpillars illustrated 

 on the web in Fig. 45 were parasited specimens that thus 

 remained after the others had crawled away. 



Shortly after becoming full grown the Tachinid grub 

 breaks through the skin of the dying caterpillar and falling 

 to the ground changes to a peculiar pupa; the outer skin of 

 the grub turns brown and becomes hard, forming a protective 

 covering for the body inside. A week or two later the insect 

 undergoes another change and emerges as a two-winged Ta- 

 chinid fly like the one that laid the egg some weeks before. 



Our observations indicate that during the last season a 

 comparatively small proportion of the caterpillars were af- 

 fected by parasites of any kind. 



