Butterflies Worth Knowing Part 15

[Ill.u.s.tration: _Photograph by Miss J. Brooks_ _See pages 17, 232_

FLASHLIGHT PHOTOGRAPH OF MONARCH OR MILKWEED b.u.t.tERFLIES IN MIGRATION]

[Ill.u.s.tration: THREE ANGLE-WINGS: UPPER SURFACE

The American Tortoise-sh.e.l.l (_see page 182_) The Red Admiral (_see page 160_) The Violet-tip (_see page 150_)]

[Ill.u.s.tration: THREE-ANGLE WINGS: LOWER SURFACE

The American Tortoise-sh.e.l.l (_see page 182_) The Red Admiral (_see page 160_) The Violet-tip (_see page 150_)]

[Ill.u.s.tration: _From a drawing by W. I. Beecroft_ _See page 163_

THE PAINTED BEAUTY Caterpillar, chrysalis, and b.u.t.terfly]

=The Red Admiral or Nettle b.u.t.terfly= _Vanessa atalanta_

Among the weedy plants which have been intimately a.s.sociated with mankind ever since his slow upward progress in civilization began, the nettle has probably played almost as important a part as the thistle.

While it lacks the winged seeds of the latter it is even more effectually protected from the attacks of vertebrate enemies on account of its irritating hairs. At any rate, nettles of various kind are widely distributed over the earth's surface, and consequently it is not surprising that the Nettle b.u.t.terfly or Red Admiral should be almost as cosmopolitan as the Thistle b.u.t.terfly. The two species are closely related in structure and habits and the life-history of the one is very similar to that of the other.

About the middle of May one may see in open fields and along sunny highways these Red Admirals flitting from flower to flower, or stopping occasionally upon green leaves in search of opportunities to lay their eggs. Should you observe them closely you might notice that some of them seemed frayed and worn while others seemed perfectly bright and fresh.

_The Life-story_

Late in May and early in June these b.u.t.terflies deposit their eggs upon the leaves of the nettles. As a rule only one or a few eggs are laid on a leaf, but when the b.u.t.terflies are abundant many leaves upon the plant may become infested. About a week later the egg hatches into a larva, which is likely to eat more or less of the empty sh.e.l.l before crawling up the stem of the plant to the unfolding buds at the top.

Here it makes its first nest by webbing together the still closed upper surface of a leaf not yet unfolded. It is thus able to furnish itself with protection from weather and enemies, as well as an abundant supply of succulent food. It remains in this first home about a week, then it casts its skin, still within its protection, and stays until it has recovered after the process. It now migrates to another larger, expanded leaf where it very cleverly proceeds to construct its second nest. In order to do this it weakens the midrib at the base of the leaf by biting nearly through it. Then it cuts a hole in the blade of the leaf at the base in such a way that the margins are made to droop, so that they can be fastened together with silk to form a little tent. We thus have a tent-like nest hanging down from the stem of the leaf on the under side of which the caterpillar will find shelter, while near at hand is the green tissue of the inner surface of the leaf waiting to be eaten. This improvised tent serves as the home during this second stage of the caterpillar. Here also the second moult commonly takes place, after which the caterpillar migrates to a new leaf and constructs its third nest. The rest of the story of the caterpillar's life consists of similar chapters. After each moult a new tent is formed and even the chrysalis is often hung within the last one.

The eggs which were laid late in May develop into b.u.t.terflies during July. These in turn lay eggs for the second brood of caterpillars most of which develop into b.u.t.terflies late in August or early in September, but some of which apparently remain in the chrysalis stage unchanged throughout the winter, and mature as b.u.t.terflies about the middle of the following May. This is the explanation of the fact mentioned at the beginning of this discussion that one can find late in spring and early in summer some b.u.t.terflies which seem worn and frayed while others seem perfectly fresh. They are all the progeny of the midsummer brood of the previous summer, but some of them have been living as full-grown b.u.t.terflies through eight long months of tempestuous weather, while others have just been disclosed from the protecting walls of the chrysalis.

The world-wide distribution of this b.u.t.terfly is shown in the statement that it occurs throughout Europe, and in North America from Newfoundland to Cuba and Guatemala. It is a safe guess that it is found in practically all localities where nettles grow.

It is not alone the a.s.sociation between a b.u.t.terfly caterpillar and its host plant which has been brought about during the long ages through which one generation has been succeeding another, but there have been also many developments of similar a.s.sociations between the caterpillars and their parasitic enemies. The Red Admiral is a good example of such a development. During its long growth as a species it has been exposed to attack by vast numbers of tiny foes which live at the expense of other insects. Several of these foes have found in the bodies of the caterpillars good opportunities for growth, so that now the Red Admiral, as a species, has to reckon with many enemies among these tiny parasites. The interaction between caterpillar host and uninvited parasitic guest has much to do with the great irregularity in the numbers of the b.u.t.terflies. It is simply another example of that complicated struggle for existence, by means of which nature keeps ever a fairly even balance of her myriad forces.

=The Painted Beauty= _Vanessa huntera_

One of the most interesting phases of the study of b.u.t.terflies is to learn how often they take advantage in their life-history of any peculiarity of the food plant which has a protective value. The Painted Beauty is an excellent ill.u.s.tration of this. The caterpillar feeds upon the leaves of the common Everlasting or Gnaphalium. This is an abundant and widely distributed plant, found along roadsides and in fields and pastures. It is notable for the woolly covering on stems, leaves, and flowers--this dry, hairy surface being so evident that the flowers will apparently continue in blossom when they have dried, hence its common name Everlasting or, as the French call a similar flower, Immortelle. (_See plate, page 161._)

The utilization of the hairs upon the leaves is begun by the mother b.u.t.terfly when she lays her egg upon the upper surface, pus.h.i.+ng it down among the hairs so that it is almost concealed. Should you be fortunate enough to find one of these eggs you would see that it is a small, yellowish green object, looking like a tiny barrel with several vertical ribs upon its surface. A few days after the egg is laid it hatches into a minute caterpillar that begins eating off the hairs where they are attached to the leaf, in such a way that it soon has a free s.p.a.ce beneath a bunch of these hairs which it has more or less matted together by means of silken thread. The little caterpillar has thus provided for itself a protecting nest that effectually conceals it from birds or other enemies. It now begins feeding upon the succulent surface of the rather thick leaf, where it has removed the hairs. After several days of such feeding it moults, still under the shelter of its hairy covering. This process of moulting and feeding continues for two or three weeks, the caterpillar occasionally making a new covering as needed for its food supply.

The later nests are likely to be made by folding two or three leaves together, binding them with silken thread. The caterpillar in doing this takes advantage of the fact that the terminal leaves are vertical before they have spread out, so that it is a comparatively simple matter to make a little house by binding their edges together with silken threads. The larva feeds upon the inner walls of the house it thus constructs, and as it becomes larger the buds and blossoms are also utilized for food.

When the caterpillar is full grown it thus finds itself fairly well concealed within a very substantial sort of a home. Many of them have the apparent good sense to realize that this is as safe a place as they are likely to find for shelter during the period of the chrysalis. So the caterpillar makes the nest especially secure near the centre of what might be called the ceiling and in this web it entangles its hind legs and hangs downward, preparatory to changing to the chrysalis. A few hours later the skin splits apart and is wriggled off, leaving the chrysalis hanging in place of the caterpillar. About a fortnight later the b.u.t.terfly emerges and crawls at once to the outside of the nest, where it rests quietly while its wings expand and its tissues harden. Then it flies away in search of the nectar of thistles and many other flowers which it visits freely.

This Painted Beauty is a wonderful example of harmonious coloring. The general tone of the upper surface of the wings is fulvous, with some distinct white markings on a blackish background at the outer angles of the front pair. There is also more or less blackish shading on the base and margin of all the wings with an indistinct row of about four dots, more or less run together, near the margin of the hind wing. The under surface of the wings is even more beautiful than the upper, and furnishes a striking example of flower-picturing. There is a little fulvous background near the middle of the front wings, but the rest of the surface is spotted and striped with blotches and circles of gray and brown in a most intricate design. On each front wing near the outer angle are three indistinct eye-spots in a row, and on the outer half of each hind wing there are two bull's-eye circles, one smaller than the other, which form the most conspicuous feature in the marking of the insect.

When full grown the caterpillars are a little more than an inch long with a general color of velvety black, marked with fine yellow lines and more or less covered with bristly spines. There is also a distinct row of whitish spots along each side beginning a short distance back of the head.

This is a widely distributed b.u.t.terfly, occurring from Canada to the Southern states and beyond. In most northern regions it seems to be two-brooded, the b.u.t.terflies commonly hibernating as adults; but sometimes the winter is pa.s.sed in the condition of the chrysalis.

Along its southern range there are three and perhaps four broods each year.

=The Painted Lady or the Cosmopolite= _Vanessa cardui_

Our story of this beautiful b.u.t.terfly ought really to begin with that of one of the most successful plants in the world. Now a plant is successful from its own point of view when it is able to multiply abundantly in many different sorts of situations and to spread easily over a large area. The plant I have in mind is the thistle, which from time immemorial has been one of the commonest neighbors of man.

It is found over the whole habitable globe, as well as in many parts which are scarcely habitable. It has many advantages in its struggle for life. The roots penetrate deeply into the soil; the thickened, spiny leaves are so protected by their juices and their spines that they are molested by very few enemies; the flower stalks are also clothed in a similar armature; and the great heads of flowers are surrounded with p.r.i.c.kly involucres that generally prevent their being eaten by browsing animals or even by phytophagous insects. The brightly colored blossoms are abundantly provided with nectar and pollen, and they attract great numbers of bees, moths, and b.u.t.terflies, in order to bring about cross-fertilization. But all of these advantages are of little significance so far as wide distribution is concerned, compared with the feathery seeds which are produced in such abundance and so generally scattered by the slightest breath of wind that the word thistle-down has come into general use to express a lightly moving object. These airy seeds have been riding on the wings of the wind all over the surface of the earth for untold millions of years. Doubtless during severe storms they may be carried thousands of miles, and it is easy to think that one of them might readily go half-way round the world before it found a resting place.

Wherever such a seed alighted and found the condition of a moist soil and slight protection, it would be likely soon to spring into growth and to start anew the development of its ancient race.

The thistle, however, has not been entirely unmolested during its aeons of existence. There has been developing along with it one of the most beautiful of our b.u.t.terflies which has received various scientific names and the common name of the Painted Lady, although it is also often called the Thistle b.u.t.terfly and the Cosmopolite, which latter t.i.tle perhaps is to be preferred. This b.u.t.terfly, however, can scarcely be considered a troublesome enemy of its host plant, for it is seldom sufficiently abundant to injure the thistle appreciably. The relation between the two is rather suggestive of that mutual toleration by which two living things develop together with advantage at least to one and without serious disadvantage to the other. The universal distribution of the food plant has led to a like distribution of the b.u.t.terfly. Consequently the Thistle b.u.t.terfly has long been recognized as the most cosmopolitan species of its group.

(_See plate, page 176._)

Aside from the wide distribution of its food plant and possibly correlated with it through the diversity of climatic conditions under which the insect has developed, this b.u.t.terfly is remarkable for its powers of flight. Many instances are known where it has been taken at sea long distances from land. This is due not only to the propensity of the individual for taking aerial journeys, but also to the fact that this is one of the b.u.t.terflies which has the instinct to congregate in swarms and to migrate long distances when thus congregated. In 1879 such a flock started from Africa and migrated to Europe.

One of the most remarkable things about this b.u.t.terfly is our ignorance of what it does with itself in winter. American entomologists are agreed that the adult b.u.t.terfly hibernates, but where it does so seems not to be known. Here is an excellent opportunity for some young naturalist to go scouting, hunting in board piles, under loose bark, or with a flashlight searching the interiors of hollow trees to find between November and April living specimens of this b.u.t.terfly. Such a discovery would be a real service to science and should at once be made known through some scientific journal. In Europe there seems to be a belief that the insect hibernates partially at least in the condition of the chrysalis.

_The Life-story_

While we may not know just where the b.u.t.terflies have been throughout the winter, we do know that in southern New England they begin to be seen in fields and along roadsides about the middle of May. Many of the specimens then have a ragged appearance which is a pretty good indication that they came from the chrysalis the fall before and have been lying concealed through all the weeks since. These b.u.t.terflies lay their small greenish, barrel-shaped eggs on the leaves of the thistle. The mother b.u.t.terfly chooses the location rather carefully and deposits only one egg upon a leaf. The b.u.t.terflies continue thus to visit flowers and to lay eggs until about the middle of June when apparently they perish.

About a week after the egg has thus been laid, it hatches into a small spiny caterpillar which does not take the trouble to devour its egg sh.e.l.l as so many other caterpillars do. Instead it crawls around to the lower side of the leaf and gnaws off enough of the silken surface of the leaf to furnish material for making a webby covering, the leaf particles being woven together by threads from the caterpillar's mouth. In this way the little creature soon provides itself with a snug enclosure which serves it as a temporary home. It remains in this home much of the time when not eating, going out occasionally to feed upon the green tissues of the adjacent parts of the leaf.

This first home of the young caterpillar, made as it is as a flat blanket upon a flat surface, can be used only by a very small larva.

Consequently, the caterpillar soon finds these quarters too cramped and it deserts them to make a new home with larger s.p.a.ce. This second nest is commonly made on the upper surface of a leaf, the edges of which are likely to be more or less drawn together and other supports connected from other leaves or a near-by stem. The caterpillar continues to use this nest number two as a place for remaining when not feeding and for protection during the process of moulting. But even this larger nest is likely to be given up about the time the caterpillar becomes half grown, and a third nest is begun in the upper part of the plant. This is likely to be very commodious, its walls being made of leaves or stems bound together by a silken web. Within this the caterpillar completes its growth, going out and in through one or more doors when it wishes to feed. Sometimes it even remains within this nest during the process of changing to the chrysalis, hanging downward from the upper part in much the same way that the caterpillar of the Painted Beauty b.u.t.terfly does. In case it leaves the nest when fully developed it generally finds a place near-by in which to pupate.

About ten days after the caterpillar has changed to a chrysalis it changes again to the adult b.u.t.terfly. In southern New England these b.u.t.terflies appear about the middle of July and lay eggs soon afterward, these eggs hatching into b.u.t.terflies that change to chrysalids and change again to b.u.t.terflies late in August or early in September. This autumn brood doubtless furnishes the b.u.t.terflies that will be seen upon the wing the following May, so that it is pretty certain that they must find some shelter in which to pa.s.s the intervening months.

The full-grown caterpillar of the Thistle b.u.t.terfly is about one and a quarter inches long and of a general yellowish color, more or less marked with blackish as well as with paler lines of color. There are many transverse rows of spines along the segments, each yellowish spine having a circle of smaller ones at the top.

Notwithstanding its fondness for thistles, these caterpillars occasionally feed upon various other plants. One might readily expect them to be able to live upon other composites upon which they are found, but it seems a bit strange that they should be recorded as being "especially fond of mallows."

=The Mourning-cloak= _Vanessa antiopa_

One of the most scholarly students of American insects has happily called the b.u.t.terflies "the frail children of the air." It seems a fitting term for creatures so ethereal that they are readily wafted on the wings of the slightest breeze and so delicate in structure that they are likely to be sadly mutilated by the lightest touch of human hand. Such creatures one would say belong to regions of perpetual summer and have no place in the blizzard-swept winters of our Northern states.

Yet if one goes into the snow-clad woods during one of the midwinter thaws one is likely to see in every open glade several dark-colored b.u.t.terflies flitting from tree to tree, or resting with expanded wings in the sunniest spots. These b.u.t.terflies obviously have endured the coldest weather and if they are to survive until another season must continue to endure still more. This species is commonly called the Mourning-cloak b.u.t.terfly--not a particularly happy name for so beautiful an insect. In England it has the more suggestive t.i.tle of Camberwell Beauty, and country boys are said to call it the Yellow Edge b.u.t.terfly. Its general life-story has already been told on pages 112-115.

The caterpillars of the Mourning-cloak b.u.t.terflies are restricted to comparatively few food plants. In regions where they are not especially abundant, they are likely to be found upon willow, poplar, or elm. In general, as many observations indicate, they are as likely to be found upon any one of these food plants as upon either of the other two; but in certain localities where they become especially abundant it seems that they are more likely to occur upon the elm. On this account they have been called the Spiny Elm caterpillars. There is considerable evidence to show that they prefer the American elm to other species of the genus, although in the case of willow and poplar there seems to be little if any preference as to the species.

Miss Caroline G. Soule has seen the b.u.t.terflies depositing their eggs upon the white and canoe birch, and it has been recorded as feeding in Labrador and Europe upon a species of birch. There is one record of the caterpillars having been found feeding upon the hackberry, and also of their having fed greedily upon the leaves of rose bushes, and still another of their having almost defoliated a pear tree. Linden and nettle are also included in the European lists of the food plants of this species. (_See plates, pages 145, 176._)

It is evident, however, that all of these, except the three first named--willow, poplar, and elm--are to be regarded as exceptional cases, and that the normal food of the species is the foliage of a plant belonging to one of these three genera.