Butterflies Worth Knowing Part 6

In the orange-growing regions of the Southern states the caterpillars of this b.u.t.terfly feed freely upon the leaves of citrus fruits and they are often called "orange puppies" or "orange dogs." Probably their curious appearance and their habit of resting for long periods upon leaf or twig gave rise to this name. In the region indicated the life-history of the insect may be summarized thus:

The mother b.u.t.terfly deposits the eggs singly upon the young growth of orange or other citrus fruit trees, generally near the tips of leaves or branches. About a week later each egg hatches into a caterpillar that feeds upon the young leaves, resting upon the lower surface when not eating. After a few days of this feeding the caterpillar becomes too large for the skin with which it was born and it moults, coming forth with a new skin which soon hardens so that it can begin feeding again. A week or so later it moults for the second time, and continues these processes of feeding and moulting until full grown, which is perhaps a month from the time of hatching from the egg. At first the caterpillars eat only the succulent young leaves and branches, but as they grow larger they feed more freely upon the older foliage. They are very voracious and when abundant may often do much damage especially to young trees. When ready to change to the chrysalis each caterpillar attaches itself by silken threads to the bark of the trunk or branch of the tree. Here it changes to a chrysalis which takes on a color so similar to that of the bark that the insect is surprisingly difficult to discover. A fortnight or so later it changes again into a fully developed b.u.t.terfly that sallies forth in search of the nectar of flowers. (_See plate, page 240._)

These "orange dogs," like the caterpillars of other Swallowtail b.u.t.terflies, have curious yellow scent organs which, when the caterpillar is disturbed, protrude from the upper surface just behind the head. These give forth a very disagreeable odor which is believed to serve the purpose of repelling birds and possibly other enemies. It has been noticed that these caterpillars are not molested by birds although they are attacked by various insect enemies. Each mother b.u.t.terfly is known to be able to deposit four or five hundred eggs and it has been suggested that the injuries of the caterpillars may be checked by shooting the b.u.t.terfly upon the wing with cartridges loaded with small bird shot. In the South there are several broods in a season.

The life-history of this species in more northern regions differs in the choice of the food plant and the number of broods. It feeds upon various members of the rue family, including common rue and p.r.i.c.kly ash, as well as upon certain poplars and probably other trees. It is two brooded and apparently winters as a chrysalis. The b.u.t.terflies of the first brood come from the chrysalis about the last of May and are found on the wing during June. Those of the second brood come from the chrysalis about the last of July and are found on the wing during August and September. The length of time required from the laying of the egg to the emergence of the b.u.t.terfly varies greatly with the locality and the temperature. It commonly extends over a period of four or five weeks.

[Ill.u.s.tration: _From a drawing by Mary E. Walker_ _See page 62_

GIANT SWALLOWTAILS Visiting blossoming branches of the orange tree. (Reduced)]

[Ill.u.s.tration: _See page 59_

BLACK SWALLOWTAIL VISITING THISTLE, SHOWING THE TONGUE PARTIALLY UNCOILED]

[Ill.u.s.tration: _Photographed from life_ _See page 83_

IMPORTED CABBAGE b.u.t.tERFLY (A good deal magnified)]

[Ill.u.s.tration: _See page 65_

THE BLUE SWALLOWTAIL Upper surface above; lower surface below]

=The Blue Swallowtail= _Laertias philenor_

The Blue Swallowtail is said to have closer affinity with the splendid b.u.t.terflies of the tropics than most of our other Papilios. The sheen of metallic color upon its wings is certainly suggestive of the broad expanse of similar colorings in the gorgeous b.u.t.terflies from South America. This species is easily recognized by the general blackness of the front wings and the basal parts of the hind ones as seen from above, about two thirds of the area of the latter being overlaid with blue-green scales that give the metallic l.u.s.tre characteristic of the species. Near the outer border of the basal half of the front wings there is a row of about five rather indistinct whitish spots, this row being continued more distinctly on the hind wings. On the under surface the white spots of the front wings are more p.r.o.nounced than on the upper, while each hind wing is brilliantly marked with about seven large orange spots, part of them fringed on one or both sides with a distinct margin of white. The extreme side borders of all four wings are distinctly marked with white crescents and the fringes on the tails as well as more or less of the darker fringes of the hind wings are of a beautiful purple color. In the males each hind wing has along the inner border a slender, pocket-like depression which is said to be the seat of the scent organs. (_See plate, page 65._)

This splendid b.u.t.terfly is a southern species. It is found from the Carolinas to California, being at times extremely abundant in certain localities over this great region. It seldom occurs as far north as New England and in a general way east of the Rocky Mountains its northern limit approximates that of forty-three degrees of lat.i.tude.

It varies considerably in size and differs greatly in abundance in different localities and different seasons.

[Ill.u.s.tration: Caterpillar of the Blue Swallowtail.

(After Riley)]

Probably the commonest food plant of the caterpillars is the Dutchman's Pipe or Aristolochia, which is frequently planted as an ornamental vine for porch adornment. It also feeds upon wild ginger or Asarum and probably upon other plants. A dozen or more eggs are laid upon a leaf by the mother b.u.t.terfly, usually in a cl.u.s.ter or grouped near together. They hatch a week or so later into small brownish caterpillars which remain together for awhile in little groups that feed side by side upon the leaf, beginning at the margin and working toward the centre. As they become larger they feed more freely and gradually disperse so that each forages for himself. As they approach maturity their appet.i.tes become voracious and their presence is often shown by the defoliated condition of the branches. They have back of the head the osmateria or scent organs which are commonly found in the other caterpillars of this genus, but the odor emitted by them is likely to be less p.r.o.nounced than usual.

[Ill.u.s.tration: TWO OF THE SWALLOWTAILS (Three fourths natural size)

The Palamedes (_see page 76_) The Giant (_see page 62_)]

[Ill.u.s.tration: _See page 67_

THE GREEN-CLOUDED SWALLOWTAIL Upper surface above; lower surface below]

When full grown the caterpillars find such shelter as they may and each spins a bit of silken web and a silken loop which hold it while it changes to the chrysalis. This chrysalis is very likely to take on the colors of the immediate surroundings and thus be rather difficult to see. If the egg was laid by one of the spring or early summer b.u.t.terflies, the chrysalis will soon change to a b.u.t.terfly which will appear toward midsummer and which may lay eggs for another brood of caterpillars. These caterpillars mature to chrysalids the same season and some of them are believed to change into b.u.t.terflies in autumn, these b.u.t.terflies hibernating through the winter; while others are believed to remain unchanged through the winter and disclose the b.u.t.terfly the following spring. This is an exceptional condition for the Swallowtails and it is worth while to make careful observations along its northern limits to learn more definitely the facts as to the winter condition.

=The Green-clouded Swallowtail= _Papilio troilus_

This beautiful b.u.t.terfly is essentially a southern species and is found over a wide range of territory from the Mississippi River to the Atlantic Ocean. It occurs as far north as New Hamps.h.i.+re and Vermont and has even been reported from Alberta, Canada. It is easily recognized by the blue-green clouding of the upper surface of the wings, the general color being velvety black with distinctive rows of yellow spots along the margins of the front wing. These spots are present also on the hind wing where they are almost changed to blue because overlaid with a general cloudiness of this color. On the under surface of the hind wings there are two rows of orange-brown spots, the inner row being nearly crescent-shaped and the outer row oblong.

In the living insect the tail projections on the hind wings are usually twisted into a vertical plane at right angles to the plane of the wings.

The caterpillars of this species feed upon the leaves of sa.s.safras and spice bush. The distribution of the b.u.t.terfly appears to be closely related to the distribution of these plants.

As is the case with so many of our Swallowtail b.u.t.terflies, the Green-clouded Swallowtail pa.s.ses through the winter in the chrysalis stage. Late in spring the b.u.t.terflies emerge and soon afterward lay their eggs singly upon the leaves of sa.s.safras or spice bush. The eggs soon hatch into lead-colored caterpillars, largely covered with spiny warts. Each caterpillar cleverly makes a protecting nest by eating out a narrow strip in the leaf which frees a flap along the margin that is turned back upon the leaf, making a case in which the larva lives. It spins a silken carpet on one side of the case and rests upon this carpet when at home. During its feeding periods it goes outside and eats the tissues of the other parts of the same leaf. It continues to occupy this first nest for a week or more by which time the rest of the leaf is likely to be pretty well consumed.

Having pa.s.sed the first moult and thus become larger and having practically eaten itself out of its first house and home the caterpillar now crawls to a larger leaf where it proceeds to make a more enduring structure. In this case it does not need to bite a channel along one side of the midrib as it did before, but instead it begins to spin silken threads transversely across the upper surface in such a way as to fold over the border of the leaf and make a tubular chamber in which it has plenty of room to move about. It uses this as its home for some time thereafter, wandering out at evening to feed upon neighboring leaves as its hunger necessitates. In this way it continues to feed and grow for a week or two. Then it finds it necessary to construct still another home, which it does by bringing together the opposite sides of a leaf, taking care to have a door-like opening at the base of the blade next the leaf stalk. This third home serves it to the end of its larval existence. It goes in and out as necessary, remaining concealed when it casts its skin and until the body tissues harden afterward. Apparently it devours the cast skin and thrusts the hard covering of the head out of the nest. Consequently these little homes are clean and sanitary and serve admirably their protecting purpose.

The full-grown caterpillars have the curious appearance of those of the other Swallowtails. The third ring behind the head is greatly swollen, making, with the rings directly in front of it, a characteristic picture suggesting a grotesque face with large eye-like spots at the top. The general color is green, darker above than below, and there are six rows of blue dots along the body. (_See plate, page 80._)

When ready to change to the chrysalis, the caterpillars desert their leafy homes and on a twig or board or stone each spins a bit of silken webbing and a silken loop. They now change to chrysalids which are likely to resemble the color of the background and which are somewhat smoother than many of the Swallowtail chrysalids. About two weeks later the b.u.t.terflies emerge.

_The Eclosion of the b.u.t.terfly_

The transformation of a chrysalis into a b.u.t.terfly is always one of extraordinary interest. Comparatively few definite descriptions of this process have been given by careful observers. One of the best of these is that written by Mr. Scudder in connection with the emergence of this b.u.t.terfly, and it is so accurate and complete that it seems worth while to quote it at length:

"The b.u.t.terfly generally emerges from the chrysalis early in the day,"

writes Mr. Scudder, "and the first signs of the immediate change are strong forward and backward movements of the chrysalis at intervals of a few seconds; perhaps the third or fourth attempt will be successful, when a click may be heard at the distance of several feet; but all the subsequent movements are absolutely noiseless, though rapid; at intervals of three or four seconds, spasmodic movements similar to the first carry on the process; first the split continues along the thorax; then it runs down either side between the legs and wings, ultimately to the tips of the antennae. As this progresses, the actions become more strenuous and more frequently repeated; with eager efforts the b.u.t.terfly pushes forward its half-detached head; now an antenna springs from its case, at once a.s.suming its natural att.i.tude; the other soon follows, and then the wings are partially drawn from their sheaths, and while in this position seem to be used as levers or arms to aid in withdrawing the rest of the body; next the legs appear, seize the upper part of the chrysalis skin, and speedily withdraw the whole body. It is now a curious-looking object, the wings wrinkled and bloated, and, although the whole process of escape lasts little more than half a minute, already twice the size of the sheaths they lately occupied. The insect crawls upward until it finds a secure resting place, and there remains until ready for flight; each half of the tongue, drawn independently from its receptacle, is rolled in a separate spiral, and now while the wings are gradually expanding the insect applies all its energies to uniting their two parts, incessantly rolls and unrolls them, and beginning simultaneously at the base, gradually fits them together by their interlocking joints; in about fifteen minutes all but the tips are perfectly united; these require nearly fifteen minutes more, and are not fairly interlocked until the wings are fully expanded, nearly a full half hour after the escape from the chrysalis; the wings, however, are still tender, and generally require two hours to stiffen. When at last the insect ventures upon flight, it is not with an uncertain flutter, but boldly and steadily, as if long accustomed to the action."

The b.u.t.terflies of this second brood of the season are likely to begin to appear early in August, continuing to become more abundant throughout that month. These lay eggs upon the same food plant and the caterpillars grow to maturity in the same way as those of the first brood. They become full grown during September or October, and then change to chrysalids which remain dormant until the following spring.

The species thus has two broods each year and pa.s.ses the winter only in the chrysalis state.

These beautiful b.u.t.terflies are likely to be found in the sort of situations where the food plants of the larvae are growing. Open groves, the borders of woods, and the margins of streams or marshes are the places where one is most likely to find spice bush and sa.s.safras. These are the places to look for these b.u.t.terflies which one may often see in graceful flight near the ground, pausing now and then to seek a sa.s.safras leaf or to sip the nectar from a flower.

=The Tiger Swallowtail= _Papilio glaucus_

One of the many things that make a study of the life-histories of b.u.t.terflies of great interest is the variations in the development of many of the species. One who follows the simplest life-story of a b.u.t.terfly and sees the egg change to larva and the larva change in size and form and color with each successive moult and then change again into the seemingly inert chrysalis, from which there finally comes the winged b.u.t.terfly--unlike the egg, unlike the larva, unlike the chrysalis--a creature of perfect beauty, wonderfully adapted to living freely in the air and sipping ambrosial nectar from the flowers--one who follows these changes with awakened vision can scarcely fail to have a sense of wonder as to the laws that govern such intricate phenomena. But the marvel is still more p.r.o.nounced in the case of those b.u.t.terflies which have two or more forms arising from the same lot of eggs in a way which science has as yet not adequately explained.

The splendid Tiger Swallowtail is an example of this dimorphism which is of especial interest because of the fact that the extra form is confined to one s.e.x and to only a part of the geographical area over which the b.u.t.terfly is found. The species occurs over a very large part of the North American continent, being found from ocean to ocean and from Canada to Florida. In the region north of approximately the fortieth degree of lat.i.tude there is but one form of the insect--the familiar yellow-and-black striped b.u.t.terfly which every one has seen visiting the lilac blossoms in May or June. South of this, however, part of the females take on an entirely different appearance, being almost wholly black with the hind wings touched with lines of blue and bordered with crescents of yellow and orange. The curious thing about it is that a certain mother b.u.t.terfly may lay a dozen eggs part of which will develop into the usual yellow form and the rest into the black form, both lots being of the same s.e.x. This black form is so entirely distinct in appearance that the two were originally described as separate species, and they were long considered such, until breeding experiments determined the precise condition. (_See plate, page 17._)

This species is of interest also for another reason. The caterpillars during their later life are remarkable examples of that curious resemblance to the head of a serpent which is thought to have a real protective value in frightening away attacking birds and possibly other enemies. The rings of the body just back of the head are much swollen and on the top of the swollen part there are two large circular marks which bear a striking resemblance to eyes. When the insect is at rest it withdraws its head and holds up the front of the body in such a way as certainly to suggest at the first glance that one is looking at the head of a small snake, an impression which is likely to be enhanced when the caterpillar pushes out the curious yellow scent organs from the ring near the top of the head, these organs taking on the forked appearance of a snake's tongue.

Obviously it is exceedingly difficult to get definite observations under natural conditions to determine whether these seeming resemblances are really of value to the caterpillar in frightening away birds or other enemies. About the only direct evidence which I have come across upon this point is found in this paragraph by Dr. J.

L. Hanc.o.c.k:

"When I recall the first sight of this larva, the impression gained of it was a most curious one. The forward mask-like face was remarkably startling. This mask, bearing eye-like spots and the light transverse ridge, gave it an aspect which might easily be mistaken for real eyes and a mouth. This contrivance is only a false face in no way connected with the real eyes and mouth. One might imagine the shock that a bird, or other predaceous enemy, would experience when looking upon this grinning mask. This is in reality the effect produced, for I have seen small birds so alarmed that they lost their appet.i.te and curiosity for these larvae after a brief glance at them. It is certain that these singular markings have the effect of terrifying their bird enemies."[B]

[B] "Nature Sketches in Temperate America," p. 146.

The yearly cycle of the Tiger Swallowtail is much like that of the related species. It pa.s.ses the winter as a chrysalis, the b.u.t.terflies coming forth just about the time that the lilacs bloom. They remain upon the wing for a few weeks and deposit their eggs upon a great variety of trees and shrubs, for the food plants of the larvae are unusually varied and include tulip trees, birches, wild cherries, apples, poplars, ash, and several other common trees or shrubs. These eggs soon hatch into caterpillars that feed upon the leaves and make for themselves resting places by spinning a web of silk transversely across the surface of the leaf. They remain upon these silken webs when not feeding and in later life are likely to cause the leaf on which the web is made to curl into a partial tube. When fully developed they change to chrysalids which give forth the summer brood of b.u.t.terflies in July and August. These in turn lay eggs for the caterpillars which change to chrysalids in autumn and remain in that condition until the following spring.