The little pocket that I have thus described is situated upon the seventh segment of the abdomen. Just back of it there are two other openings which are even more curious in their structure. These are provided with some slender tentacles on which there are circles of hairy spurs. These structures are a great puzzle to naturalists. It is difficult to explain what they are for unless we assume that they relate in some way to the honey-dew pocket on the seventh ring. The only plausible explanation is that these serve to advertise to the ants, by giving off a distinctive odor, that there is nectar near at hand to be had for the asking. They would thus be analogous in a way to the fragrant scent of flowers which is for the purpose of advertising to the bee the fact that nectar or pollen or both are near at hand and may be had for the asking. In the case of these caterpillars, however, if this is the true explanation it is a most wonderful provision and one which would be likely to tax the ingenuity of man's mind for a long while before it was originated.
So this little butterfly which greets us in every spring, like "a violet afloat," to quote Mr. Scudder's happy phrase, is full of interest at all stages of its existence. It should lead one to a new respect for the familiar things in the natural world when one learns how baffling to the wits of the wisest scientist is this little creature with its protean forms and the wonderful structure of its caterpillars.
Scudder's Blue
Rusticus scudderi
This beautiful little butterfly is perhaps the most richly colored of all our northern Blues. The upper surface of the wings in the male is a nearly uniform hue, except for a narrow dark border around the margin. In the female there is, in addition, a series of black-centred orange spots inside of the black border, the series being more prominent on the hind wings than on the front ones. The under surface is very pale with distinct marks in black scattered over the basal two thirds, with a row of orange spots outside of these and another row of small blackish spots just inside of the blackish border stripe.
This butterfly is a northern species. It occurs in New England, New York, and Michigan, and thence extends far north into Canada. The caterpillar feeds upon blue lupine and apparently the butterfly is likely to be found in most places where this plant grows. The eggs are laid upon the leaves or stems and the little caterpillars come out of the shells through small holes which they have gnawed.
"The caterpillar," wrote Mr. Scudder, "has a very extensible head and flexible neck, and its manner of feeding immediately after birth is rather remarkable; it pierces the lower cuticle of the leaf, making a hole just large enough to introduce its minute head, and then devours all the interior of the leaf as far as it can reach—many times the diameter of the hole—so that when the caterpillar goes elsewhere, the leaf looks as if marked with a circular blister, having a central nucleus; the nearly colorless membranes of the leaf being all that is left, and at the central entrance to the blister the upper membrane only." Later in its life it often modifies this feeding habit somewhat, and as it approaches full growth it is likely to devour the entire blade of the leaf.
These larvae have the curious nectar-secreting glands on the seventh abdominal segment which are discussed in connection with the preceding species. Many ants are attracted by this secretion so that it often happens that the easiest way to find the caterpillars is to look for these attendants. In New England there are two broods of the butterfly, one appearing early in June and the other late in July.
The Tailed Blue
Everes comyntas
The tiny, threadlike, white-tipped tail projecting from the hind angle of the hind wings distinguishes this species at sight from any other found in eastern North America. The species, however, occurs clear to the Pacific Coast and ranges north and south over most of the northern continent. The small slug-like caterpillar feeds upon the flowers of various clovers and other legumes.