From a drawing by W. I. Beecroft
The Mourning-cloaks subsist upon a considerable variety of liquid food which they suck through their long tongues. In spring, when they first come from their winter quarters, they visit the stumps of recently cut trees and suck the exuding sap, a habit which they continue whenever opportunity offers. Mr. W. F. Fiske has noticed that they commonly sip the sap of maple twigs where the squirrels have gnawed the bark. A little later they visit the willow catkins to suck the nectar secreted by these blossoms, and still later they hover about the delicate blossoms of the mayflower, or trailing arbutus, for a similar purpose. Probably many other flowers are thus rifled of their sweets, although this butterfly seems to be a less regular visitor to flowers than are many of its allies. A little later, when the aphids, or plant-lice, have become sufficiently abundant so that the so-called "honey dew" is to be found upon the infested shrubs, these Mourning-cloaks sometimes sip the liquid sweet from the surface of the leaves. In April and May they occasionally visit the flowers of moosewood, and later in the season have been observed upon the blossoms of the common milkweed. From the time the early apples ripen these butterflies may often be seen beneath the orchard trees, sipping the liquids of the fallen and decaying fruit.
The Parasites of the Eggs
One fine spring morning I came upon a Mourning-cloak depositing a cluster of eggs upon a willow twig. She was so busily engaged that I was able to draw near and watch the operation for some time before she flew away. As soon as she was gone I was much interested to see a tiny parasitic fly running eagerly over the newly laid eggs, and this fly also was so busily interested in her work that I was able to cut the twig off and sit down to observe at leisure through a lens the actions of the insect. I dictated to a companion my notes of these observations and so was able to get rather a complete record of the process of oviposition.
The tiny fly would stop over one of the butterfly eggs, holding its body vertical with the hind legs far back and the other legs so straightened out as to hold the front of the body high up. Then it would insert its tiny ovipositor through the egg shell and proceed to deposit an egg of its own inside of the larger egg of the butterfly. At least it seemed a safe assumption that this was what happened although of course it was impossible to see the smaller egg at the time. While thus engaged the antennae of the tiny fly were bent directly downward to the egg beneath. In about a minute the fly withdrew its ovipositor and after running around for a few seconds again settled upon another egg and repeated the operation. Then it tried again on a third egg, after which I got out my watch and began timing the process. These are the results in the case of the next dozen eggs that were laid. It required:
| 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.