THE TRIBE OF THE ANGLE-WINGS 179 



90 sec. to lay egg No. 9. Then fly moved around 42 sec. 



It thus required an average of about two minutes per 

 egg for the laying of these fifteen eggs. I then caught the 

 little fly and sent her to Dr. L. O. Howard, our greatest 

 authority on this group of insects, to learn the name of the 

 parasite. He identified it as Telenomus graptae, a well- 

 known parasite of the eggs of the Mourning-cloak and 

 related butterflies. 



The most interesting thing about this observation was 

 the fact that the little fly had apparently begun its opera- 

 tion before the mother butterfly had finished laying her 

 cluster of eggs. There were thousands of willow twigs 

 in the immediate vicinity. How did this tiny creature 

 arrive at this particular place at the particular moment 

 when from its own point of view it was most needed? 

 Had it been riding around upon the body of the butterfly 

 waiting for the time when she should lay the eggs? Or 

 was it attracted to them from somewhere in the immedi- 

 ate vicinity? That this early arrival probably takes place 

 generally is indicated by the fact that a similar observa- 

 tion had been made in the White Mountains by Prof. 

 C. W. Woodworth. 



The history of the egg parasite after the laying of the 

 egg seems to be comparatively simple. It soon hatches 

 into a tiny larva that develops within the shell at the ex- 



