Butterflies Worth Knowing Part 24

In many orders of insects there are whole families whose larvae are habitually carnivorous, feeding entirely upon other kinds of insects.

This is especially so in case of the beetles, the flies, the true bugs, and the great order to which the bees and wasps belong. Among the scale-winged insects, however, carnivorous caterpillars are rare, seldom occurring among the moths and in hardly more than one species among the b.u.t.terflies. This one exception is the modest-looking little b.u.t.terfly fancifully called the Wanderer, perhaps because instead of frequenting the flowery fields where other b.u.t.terflies congregate it wanders in and out among the alders by brooks and ponds, alighting oftener upon a leaf or twig than upon a flower--the latter apparently lacking for it the attraction it has for other b.u.t.terflies.

If you watch one of these copper-hued creatures for awhile, however, you will soon see that its wandering is not aimless but has rather a method all its own. Perhaps you will see it alight upon an alder twig on or above which you are likely to notice curious woolly white excrescences. If you are close enough you will probably see the b.u.t.terfly uncoil its tongue and sip up a liquid on twig or leaf--the exudations of the woolly aphids that make up the supposed excrescence and suck the sap from the bark. Much of this sap pa.s.ses through the bodies of the aphids and collects in liquid globules on twigs and leaves, forming a sort of honey-dew which is much sought after by flies, wasps, and other insects. It seems to form the chief sustenance of these Wanderers.

But many of these b.u.t.terflies have another purpose besides that of sipping the honey-dew. Should you watch one of the mother b.u.t.terflies carefully you would be likely to see her alight on or near a colony of woolly aphids and run rather rapidly over them in a wasp-like manner, finally stopping long enough to lay a tiny, roundish, slightly flattened egg upon the twig, generally on the under side, and only one in a place. Then she may continue her way, wandering lazily along the alder-bordered stream.

Let us now centre our interest upon the egg. Three or four days later it hatches into a curious caterpillar. Instead of having mouth parts fitted for biting leaves as is the case with most b.u.t.terfly larvae, it has one fitted for grasping, piercing, and sucking the juices of the plump bodies of the aphids, which it finds hard by its place of birth.

It also has silk spinnerets connected with its mouth, so it is able to spin a web to shelter it from being run over by its intended victims.

The newly hatched larva is not slow to take advantage of the facilities with which it is provided. It at once begins to spin a web above and around itself, from the end of which it reaches out for the nearest aphids, sucking their life-blood and casting their empty skins to the discard of its protecting web. The skins thus serve as an additional shelter so that, as the caterpillar moves forward, increasing the number of its victims from day to day, it extends its web and the protection of the cast skins intermingled with it, while through all--the cast skins, the silken web, and even the hairs on the body of the caterpillar--there runs a woof of the woolly excretion--effectually concealing the larva from sight.

The woolly aphids thus serve as the sole food of the caterpillar during its brief life as a larva. Perhaps because of the pre-digested nature of its food, it is able to mature much sooner than most b.u.t.terfly larvae. In about eleven days after hatching it is ready to change to a chrysalis, having undergone during this period only three moults, instead of at least four as with other caterpillars. Each caterpillar then changes to a chrysalis which is remarkable because the form and color of its back bears a striking resemblance to the face of a miniature monkey. It remains in this condition nearly a fortnight and then emerges as a b.u.t.terfly.

In New England and the Northern states the short life of the larva enables this insect to mature three broods each season. Farther south there are probably more, for this species is widely distributed in eastern North America, occurring from Nova Scotia to Georgia and west to the Mississippi Valley.

=The American Copper= _Heodes hypophlaeas_

This little b.u.t.terfly is one of the most generally abundant insects in the northern part of North America. It commonly occurs from ocean to ocean, from the Hudson Bay region to the lat.i.tude of Georgia, and it flies freely in city parks and village yards as well as in the more open s.p.a.ces of field and forest. When seen through a lens it is very beautifully colored, the coppery red of the wings being overspread with conspicuous black dots and a touch of orange around the outer border. The expanded wings measure just about an inch, so that this is one of the smallest of our common b.u.t.terflies.

The caterpillars of the American Copper feed upon sorrel, one of the commonest weedy plants of waste places everywhere. The rusty red blossoms of the sorrel harmonize in color with the color of the b.u.t.terfly, which is frequently to be seen flying slowly above the plants, stopping now and then to lay its eggs singly upon the leaves or stems. Each egg soon hatches into a curious caterpillar, which looks more like a slug than the usual type of b.u.t.terfly larva. It feeds upon the succulent tissue of the sorrel leaf, at first biting small holes in the under surface. As it gets larger it feeds more freely and is likely to make channels instead of holes. It matures in about three weeks, changing into a chrysalis under the shelter of a stone or board. A little later it again changes to a b.u.t.terfly.

There is an interesting variation in the number of broods of this b.u.t.terfly each season. In regions where it has been studied it has been found to be double-brooded in northern New England and triple-brooded in southern New England and the Atlantic states. It is probable that in its far northern home in the Hudson Bay territory it is only single-brooded. It is thought that the insect hibernates as a chrysalis.

These little b.u.t.terflies are so small and fly so near the ground that they are likely to be overlooked by the casual observer. They frequently alight to sun themselves or to sip nectar from many kinds of flowers. They begin their day's work early in the morning and continue well into the evening. Then they find a roosting-place, head downward upon a blade of gra.s.s, where they sleep until wakened by the morning suns.h.i.+ne.

[Ill.u.s.tration: _From a drawing by W. I. Beecroft_

FIVE INTERESTING b.u.t.tERFLIES

The Spring Azure (_p. 258_) at the top; the Falcate Orange-Tip (_p. 94_) next; the Bronze Copper (_p. 257_), female, next; the Spring Azure (_p. 258_) resting on a leaf, next; and the Great Purple Hair-streak (_p. 243_), female, below.]

[Ill.u.s.tration: _See page 245_

STAGES OF THE GRAY HAIR-STREAK]

=The Bronze Copper= _Chrysopha.n.u.s thoe_

This b.u.t.terfly is nearly twice as large as the American Copper to which the female of the present species bears a striking resemblance.

The Bronze Copper is a rare species, occurring from New England nearly to the Rocky Mountains. The slug-shaped yellowish green caterpillar feeds upon dock and related plants. (_See plate, page 256._)

_Synopsis of the Coppers_

_The Wanderer_ (_Feniseca tarquinius_). Wing expanse 1 1/4 inches.

Upper wing surface tawny brown, each wing more or less marked with dark brown spots, the distinction between the colors being clear-cut, and the lines between having an angular effect. Lower surface of front wings similar in colors to upper with dark spots rectangular. Under surface of hind wings mottled with irregular spots of pale brown.

_American Copper_ (_Heodes hypophlaeas_ or _Chrysopha.n.u.s hypophlaeas_). Wing expanse 1 inch. Upper surface of front wings tawny orange with margins and rectangular spots blackish. Upper surface of hind wings coppery red with a tawny orange band on outer margin. Lower surface of front wings much like upper surface; that of hind wings grayish marked with dark spots and an orange line near the margin.

_Bronze Copper_ (_Chrysopha.n.u.s thoe_). Wing expanse 1 1/2 inches.

_Male._ Upper wing surface coppery brown marked with dark spots and a tawny orange sub-marginal band along outer margin of hind wings. Under surface of front wings lighter orange with blackish spots and of hind wings grayish with blackish spots and an orange sub-marginal band.

_Female._ Upper surface of front wings tawny orange with blackish spots.

THE TRIBE OF THE BLUES

These beautiful little b.u.t.terflies are well named, for the majority of them are colored in exquisite tints of blue. They are distinguished from the Coppers by this blue coloring, as well as by the fact that the spines on the under side of the tarsi are arranged in rows rather than in cl.u.s.ters and are comparatively few in number. The body is rather slender and the under surfaces of the wings are generally dotted in a characteristic fas.h.i.+on. Most of the two score or more species found in North America occur on the Pacific Coast or in the Southwest, less than half a dozen being common in the eastern region.

=The Spring Azure= _Cyaniris ladon_

For a wee bit of a gossamer-winged creature that expands scarcely an inch across its outstretched wings, the Spring Azure has caused American scientists an immense amount of patient labor. Over the vast territory from Labrador across to Alaska and south to the Gulf of Mexico, this little blue b.u.t.terfly exists in so many different forms that it requires special a.n.a.lytical keys to separate them. Not only does it vary geographically so that in one locality we find one form and in another a different form, but it also varies seasonally to a marked degree. As one would expect there is a striking difference in its annual cycle between Labrador and the Gulf Coast. In the far northern region there is but one brood a year, while in the southern region there are at least two and perhaps more.

The variations in this b.u.t.terfly are shown by the differences in the marking of both surfaces of the wings. These markings may run from a faint blackish border along the extreme margin and a few faint dots upon the under surface, to a wide black margin around the wings and a deep abundant spotting of the under surface. The markings of the various forms are so uniform that the varieties are easily distinguished. It is beyond the scope of this book to attempt to differentiate all these varieties but any reader interested will find an admirable summary of the conditions ill.u.s.trated by an excellent plate in Comstock's "How to Know the b.u.t.terflies." The species as a whole may be known from the fact that the upper surface is blue, the lower surface ash-gray, more or less spotted with dark brown, and the wings are without tails. (_See plate, page 256._)

_The Strange Structures of the Larvae_

A remarkable variation of the adults is sufficient to give this species a special interest, but the larvae also have a unique attraction for the naturalist. The mother b.u.t.terflies lay their eggs upon the flower buds of various plants, especially those which have cl.u.s.tered racemes of blossoms. These eggs hatch into minute slug-like larvae which feed upon the buds, commonly burrowing through the calyx lobes and devouring the undeveloped stamens and pistils inside. They finally change to chrysalids, which are more or less securely attached to a central flower stalk, from which in due time the b.u.t.terflies emerge. So far there is nothing remarkable about this story of the life of the Spring Azure, but that is yet to come.

These little caterpillars are subject to attack by tiny parasitic flies which lay eggs in their bodies. Each egg hatches into a still more tiny maggot that lives at the expense of the tissues of the caterpillar and finally kills it. When one of these little caterpillars has its head buried in the round ball of a flower bud, about half of its body is exposed defenseless, so that the little fly that lights upon it to lay her egg cannot even be dislodged by the head of the caterpillar, as is often the case with other species.

There is a very curious provision for defense, however. If you look carefully through a lens at the hind part of the body you will find a little opening on the back of the seventh abdominal ring. This opening leads to a sort of tiny pocket, a pocket which the caterpillar can turn inside out when it so desires. Now the curious thing about it is that the caterpillar, while this pocket is concealed in its body, is able to secrete in it a drop of liquid which we presume to be sweet to the taste. When the little pocket is partly filled with this drop of liquid the caterpillar turns it inside out in such a way that the liquid drop remains in position on top of the protruded pocket.

Perhaps you ask what is the good of all this complicated arrangement?

If you could see what happens when the little drop of what--for lack of a better name--we shall call honey-dew is exposed, you would begin to guess the reason. Wherever these larvae are found you will also find many ants wandering round among them, and the moment the honey-dew appears these ants begin to sip it up. When it is all gone the little caterpillar draws in its pocket again and presumably begins to store up another bit of liquid. It is certainly a curious example of what the naturalists call symbiosis, which simply means a living together of two animals, each helping the other in some way. In this case it is easy enough to see how the caterpillar helps the ant, but perhaps you are wondering in what possible way the ant may help the caterpillar. I hardly dare give the most plausible explanation for fear some one will cry out, "Nature-faker!" But fortunately the explanation is based upon at least one precise observation by W. H.

Edwards, one of the most careful and reliable naturalists America has produced, who lived before the recent era of Nature-fakers and was never accused of sensationalism. Mr. Edwards saw an ant drive away from one of these caterpillars a little parasitic fly which apparently was searching for a victim. Consequently, it would appear that the ants helped the caterpillars by protecting them from these arch enemies.

This is by no means an isolated example of the relations between ants and other insects. It has been known for hundreds of years that the ants use the aphids as a sort of domestic milk-producer, attending the aphids at all times and even caring for their eggs throughout the winter season. As the plant-lice live in colonies, sucking the sap of their host plant, they are attended by great numbers of ants that feed upon the honey-dew which pa.s.ses through their bodies. In many cases the ants have been observed to stroke the aphids with their antennae in a way which seems to induce the aphid to give out a drop of the sweet liquid for the ant to lap up. In a similar way these ants seem sometimes to stroke these little caterpillars with their antennae and thus to induce them to turn their little pockets inside out with the drop of liquid at the tip. This is certainly an unusual and most interesting relation between two insects far separated by their structural characters.

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 a.s.sume 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 a.n.a.logous 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 b.u.t.terfly 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 b.u.t.terfly 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 b.u.t.terfly 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 b.u.t.terfly 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 sh.e.l.ls 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 b.u.t.terfly, one appearing early in June and the other late in July.