180 BUTTERFLIES 



pense of the contents. It finally changes to a pupa which 

 in turn changes to the little fly that gnaws a hole through 

 the egg shell and emerges to the outer world. 



The Parasites of the Caterpillars 



After hatching from the egg, the Mourning-cloak cater- 

 pillars are also subject to the attacks of various parasites. 

 One of these is quite minute, not a great deal larger 

 than the egg parasite. It is a tiny four-winged fly which 

 deposits many eggs in a single caterpillar. The eggs 

 hatch into tiny maggots that grow at the expense of the 

 caterpillar, finally killing it and changing to four-winged 

 flies again. As many as 145 of these parasites have been 

 known to emerge from a single dead caterpillar. These 

 little flies are called Chalcids 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 Ichneu- 

 mon flies. In the case of these, only one or two parasites 

 develop in each caterpillar or chrysalis. 



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

 certain two-winged flies, called Tachinid flies, that de- 

 velop at the expense of the caterpillars. In New Hamp- 

 shire, 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 the figure below. 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 



