INTRODUCTION 43 



fly, looking much like a large housefly, lays a small whitish 

 egg upon the skin of a caterpillar. This egg is glued 

 tightly and is large enough to be readily seen by the un- 

 aided eye. It hatches into a tiny larva that eats its way 

 through the part of the shell glued to the caterpillar's skin, 

 and through the latter at the same time. So the newly 

 hatched Tachina larva finds itself in the body of its cater- 

 pillar host. It lives there, absorbing the fatty juices 

 around it until at last it either kills or stupefies its un- 

 fortunate victim. It has then become full grown as a 

 larva, and its last larval skin hardens into a brown pupa- 

 case within which the little creature changes into a pupa. 

 It may or may not have burrowed through the skin of the 

 caterpillar before this happened. A little later the pupa 

 changes to a Tachina fly which breaks apart the pupa case 

 and flies out into the world. 



It has lately been found, however, that many Tachinids 

 have much more complicated life-histories than this. I 

 have already discussed some of the more important of these 

 in my book entitled, "Seeing Nature First" (pages 

 150-158). 



One can frequently rear parasites from the chrysahds of 

 butterflies, but in many cases it is probable that these be- 

 gan their parasitic development in the caterpillars, which 

 were able to change to chrysalids before being killed. 

 In some cases, however, the chrysalids seem to be attacked, 

 especially by certain Ichneumon flies. 



Rearing Butterflies From Caterpillars 



There are few tilings in the world more interesting to 

 watch than the wonderful changes wliich a moth or butter- 



