94 sec. to lay egg No. 4. Then fly moved around 26 sec. 120 " " " " " 5. " " " " 27 " 83 " " " " " 6. " " " " 20 " 92 " " " " " 7. " " " " 22 " 75 " " " " " 8. " " " " 40 " 90 " " " " " 9. " " " " 42 " 102 " " " " " 10. " " " " 15 " 120 " " " " " 11. " " " " 21 " 120 " " " " " 12. " " " " 18 " 60 " " " " " 13. " " " " 25 " 120 " " " " " 14. " " " " 25 " 60 " " " " " 15. " " " " 50 " 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 operation 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 immediate vicinity? That this early arrival probably takes place generally is indicated by the fact that a similar observation 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 expense 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 caterpillars 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.