4i6 THE ANIMALS AND MAN 



are free and independent creatures. From the chrysalid 

 of a butterfly or moth there will often come not a butterfly 

 but numerous tiny four-winged gnats, called ichneumon 

 flies. This is what happened. When the butterfly cater- 

 pillar was crawling about a female ichneumon darted down 

 on it, and with her sharp ovipositor either laid several eggs 

 beneath its skin or glued them to its outer surface. These 

 eggs hatched in two or three days as tiny white ichneumon 

 grubs, which immediately burrowed deep into the cater- 

 pillar and lay there feeding on the blood and tissues of its 



Fig. 208. Larva of a sphinx moth, with cocoons of a parasitic ichneumon 

 fly. (Natural size.) 



body. But the caterpillar went on eating and finally changed 

 into a chrysalid, with the ichneumon grubs still inside. Soon 

 the grubs, having eaten up most of the body of the developing 

 butterfly and thus killed it, changed into tiny pupae, and 

 later into fully developed ichneumon flies which gnawed 

 their way out through the horny case of the dead chrysalid. 

 One of the most interesting ichneumon flies is Thalessa, 

 which has a remarkably long, slender, flexible ovipositor. 

 Another insect, known as the pigeon horn-tail (fig. 209), 

 upon which Thalessa preys, deposits its eggs by means of 

 a strong, piercing ovipositor, half an inch deep, in the trunks 

 of growing trees. The young or larval horn-tail hatches 



