b.u.t.terflies Worth Knowing.

by Clarence M. Weed.

PREFACE

In this little book an attempt has been made to discuss the more abundant and widely distributed b.u.t.terflies of eastern North America from the point of view of their life histories and their relations to their surroundings. In so doing I have of course availed myself of the written records of a host of students of b.u.t.terflies, without whose labors no such volume would be possible. Among these two names stand out preeminent--William H. Edwards and Samuel H. Scudder. Each was the author of a sumptuous work on American b.u.t.terflies to which all later students must refer, both for information and for inspiration. Many others, however, have made notable contributions to our literature of these ethereal creatures. Every seeker after a knowledge of b.u.t.terflies will soon find himself indebted to the writings of such investigators as the Comstocks, Denton, d.i.c.kerson, Dyar, Fernald, Fiske, Fletcher, French, Hanc.o.c.k, Holland, Howard, Longstaff, Newcomb, Riley, Skinner, Wright, and many others. I am glad to express my obligations to all of these for the a.s.sistance their records have given in the preparation of this book.

While a vast amount of knowledge of b.u.t.terflies has already been discovered there is still more to be learned concerning them, and throughout these pages I have attempted to indicate the more important opportunities awaiting investigation. The day of the field naturalist has come again and the b.u.t.terflies are well worthy of careful observations by many interested students.

The ill.u.s.trations in the book require a word of credit. The eleven color plates of adult b.u.t.terflies with wings spread have been made direct from a set of the remarkable transfers which Mr. Sherman F.

Denton has been preparing for the last quarter-century, this particular set having been prepared especially for this book.

Transfers of this sort were used as insets in Mr. Denton's work on the "Moths and b.u.t.terflies of the United States," published in a limited edition by J. B. Millet Company, Boston. The other plates not reproduced from photographs are from drawings by Miss Mary E. Walker or Mr. W. I. Beecroft. In case the photographs are not of my own taking, credit is given beneath each. Two of my photographs have already appeared in "Seeing Nature First" and are here used by permission of its publishers, J. B. Lippincott Company.

C. M. W.

STATE NORMAL SCHOOL, Lowell, Ma.s.s.

PART I

INTRODUCTION

In popular esteem the b.u.t.terflies among the insects are what the birds are among the higher animals--the most attractive and beautiful members of the great group to which they belong. They are primarily day fliers and are remarkable for the delicacy and beauty of their membranous wings, covered with myriads of tiny scales that overlap one another like the shingles on a house and show an infinite variety of hue through the coloring of the scales and their arrangement upon the translucent membrane running between the wing veins. It is this characteristic structure of the wings that gives to the great order of b.u.t.terflies and moths its name Lepidoptera, meaning scale-winged.

In the general structure of the body, the b.u.t.terflies resemble other insects. There are three chief divisions: head, thorax, and abdomen.

The head bears the princ.i.p.al sense organs; the thorax, the organs of locomotion; and the abdomen, the organs of reproduction.

By examining a b.u.t.terfly's head through a lens it is easy to see the princ.i.p.al appendages which it bears. Projecting forward from the middle of the top is a pair of long feelers or antennae. Each of these consists of short joints which in general may be divided into three groups: first, a few large joints at the base connecting the feeler with the head; second, many rather small joints which make up the princ.i.p.al length; third, several larger joints which make up the outer part or "club" of the antennae. In the case of the Skippers, there are in addition a number of small joints coming to a sharp point at the end of the club. Just below the insertion of the antennae on each side of the head are the large compound eyes, which are almost hemispherical. With a powerful gla.s.s, one can see the honeycomb-like facets, of which there are thousands, making up each eye. Just below the eyes there are two hairy projections, called the palpi, between which is the coiled tongue or sucking tube. (_See plate, page 64-65._)

[Ill.u.s.tration: b.u.t.terfly Antennae, magnified. (From Holland)]

Anatomically the thorax is divided into three parts--the prothorax, the mesathorax, and the metathorax; but the lines of division between these parts are not easily seen without denuding the skin of its hairy covering. The prothorax bears the first pair of legs. The mesathorax bears the front pair of wings and the second pair of legs. The metathorax bears the hind pair of wings and the third pair of legs. In many b.u.t.terflies, the first pair of legs are so reduced in size that they are not used in walking.

The abdomen is composed of eight or nine distinct rings or segments, most of which have two spiracles or breathing pores, one on each side.

It also bears upon the end of the body the ovipositor of the female or the clasping organs of the male.

b.u.t.tERFLY TRANSFORMATIONS

The b.u.t.terflies furnish the best known examples of insect transformations. The change from the egg to the caterpillar or larva, from the caterpillar to the pupa or chrysalis, and from the chrysalis to the b.u.t.terfly or imago is doubtless the most generally known fact concerning the life histories of insects. It is a typical example of what are called complete transformations as distinguished from the manner of growth of gra.s.shoppers, crickets, and many other insects in which the young that hatches from the egg bears a general resemblance to the adult and in which there is no quiet chrysalis stage when the little creature is unable to eat or to move about.

[Ill.u.s.tration: Egg of Baltimore b.u.t.terfly, much magnified.

(From Holland)]

_The Growth of the Caterpillars_

Caterpillars are like snakes in at least one respect: in order to provide for their increase in size they shed their skins. When a caterpillar hatches from the egg it is a tiny creature with a soft skin over most of its body but with rather a firm covering for its head. While we might fancy that there could be a considerable increase in size provided for by the stretching of the soft skin it is easy to see that the hard covering of the head will not admit of this. So the story of the growth of a caterpillar may be told in this way:

A b.u.t.terfly lays an egg upon a leaf. Some days later the egg hatches into a larva, which is the technical name for the second stage of an insect's life. In the case of the b.u.t.terfly we call this larva a caterpillar. The little caterpillar is likely to take its first meal by eating the empty egg sh.e.l.l. This is a curious habit, and a really satisfactory explanation of it seems not to have been made. Its next meal is likely to be taken from the green tissues of the leaf, commonly the green outer surface only being eaten at this time. The future meals are also taken from the leaf, more and more being eaten as the larva gets older.

After a few days of this feeding upon the leaf tissues the little caterpillar becomes so crowded within the skin with which it was born that it is necessary to have a larger one. So a new skin begins to form beneath the first one. Consequently the latter splits open in a straight line part way down the middle of the back just behind the head. Then the new head covering is withdrawn from the old one and the caterpillar wriggles its way out of the split skin and finds itself clothed in a new one. At first all of the tissues of the new skin are soft and pliable and they easily take on a larger size as the body of the caterpillar expands. A little later these tissues become hardened and no further expansion is possible.

This process of skin-shedding is called moulting. The cast skin is often called the exuviae. The period of the caterpillar's life between the hatching from the egg and this moult is often called a stage or instar--that is, the caterpillar up to the time of this moult is living in the first caterpillar stage or instar.

During the actual moulting the caterpillar is quite active in freeing itself from the exuviae. But as soon as it is free it is likely to rest quietly for some hours while the tissues of the new skin are hardening. Then it begins feeding upon the leaf again and continues taking its meals at more or less regular intervals for several days.

By that time it will again have reached its limit of growth within this second skin and the process of moulting must be repeated. It takes place in the same way as before and the caterpillar enters upon the third instar of its larval life.

This process of feeding and moulting is continued for several weeks, the number of moults being usually four. During the later stages the increase in size is more marked each time the skin is shed, until the caterpillar finally reaches its full growth as a larva and is ready for the wonderful change to the quiet chrysalis in which all its caterpillar organs are to be transformed into the very different organs of the b.u.t.terfly.

In the case of b.u.t.terfly larvae one of the most interesting features of the growth of the caterpillar is that of the remarkable changes in colors and patterns of marking which the caterpillar undergoes. One who had not followed these changes would often be at a loss to recognize caterpillars of slightly differing sizes as belonging to the same species. These changes commonly show a remarkable adaptation to the conditions of life, and generally tend to the concealment of the caterpillar upon its food plant. The stages of growth of the green-clouded swallowtail caterpillar are ill.u.s.trated on plate opposite page 80.

Before each moult the caterpillar is likely to spin a silken web upon the leaf surface. It then entangles its claws in the web to hold itself in place while the skin is cast. (_See plate, page 17._)

_The Change to the Chrysalis_ (_See plate, pages 32-33._)

A week or ten days after the last moult of its caterpillar growth the larva commonly becomes full fed and ready to change to the chrysalis state. The details of the way in which this is accomplished vary greatly with different b.u.t.terflies, as will be noted in the stories of many species later in this book. In general, however, the caterpillar provides a web of silk which it spins against some surface where the chrysalis will be secure and in this web it entangles its hind legs.

Sometimes there is the additional protection of a loop of silk over the front end of the body. After the legs have become entangled the caterpillar hangs downward until the skin splits open along the median line of the back and gradually shrinks upward until it is almost free, showing as it comes off a curious creature which has some of the characteristic features of a chrysalis. It is seldom at this stage of the same shape as the chrysalis. When the caterpillar's skin is nearly off this chrysalis-like object usually wriggles its body quickly in a manner to entangle a curious set of hooks attached to the upper end in the web of silken thread. This hook-like projection is called the cremaster, and it serves a very important purpose in holding the chrysalis in position.

[Ill.u.s.tration: Swallowtail Chrysalis, showing (_b_) the loop of silk over thorax. (After Riley)]

As soon as the cremaster is entangled in the web the cast skin usually falls off and for a very short period the creature hanging seems to be neither caterpillar nor chrysalis. It is in fact in a transition stage between the two, and it very soon shortens up and takes on the definite form of the chrysalis, the outer tissues hardening into the characteristic chrysalis skin.

From the fact that this chrysalis skin shows many of the characteristic features of the future b.u.t.terfly it is evident that the change from the caterpillar to the b.u.t.terfly really began during the life of the larva. The nature of the process by which this change takes place has long been a puzzle to scientists. For the making of a b.u.t.terfly is one of the most wonderful phenomena in the outer world, and it has challenged the attention of many acute observers. Some two centuries ago the great Dutch naturalist, Swammerdam, studied very carefully the development of many insects, especially the b.u.t.terfly.

He found that if he placed in boiling water a caterpillar that was ready to pupate or become a chrysalis, the outer skin could easily be removed, revealing beneath the immature b.u.t.terfly with well-developed legs and antennae. From these observations he was led to believe that the process of growth was simply a process of unfolding; that is, as Professor Packard has expressed it, "That the form of the larva, pupa, and imago preexisted in the egg and even in the ovary; and that the insects in these stages were distinct animals, contained one inside the other, like a nest of boxes or a series of envelopes one within the other." This was called the incas.e.m.e.nt theory and it was held to be correct by naturalists for nearly a century. It was discredited, however, about a hundred years ago, but not until another fifty years had pa.s.sed was it definitely replaced by another and much more convincing theory propounded by Weismann.

According to Weismann's theory, which is now well-established, the process of development internally is a much more continuous one than the external changes would indicate. So far as the latter are concerned we simply say that a caterpillar changes to a chrysalis and a chrysalis to a b.u.t.terfly, the transition in each case requiring but a very short time. Internally, however, it has been going on almost continuously from the early life of the caterpillar. The various organs of the b.u.t.terfly arise from certain germinal disks or "imaginal" buds, the word "imaginal" in this case being an adjective form of imago, so that the imaginal buds are really simply buds for the starting of growth of the various organs of the imago or adult. As the caterpillars approach the chrysalis period these imaginal buds rapidly develop into the various organs of the b.u.t.terfly. This process is helped along by the breaking down of many of the tissues of the larva, this broken-down tissue being then utilized for the production of the new organs. About the time the chrysalis is formed this breaking-down process becomes very general, so that the newly formed chrysalis seems largely a ma.s.s of creamy material which is soon used to build up the various parts of the b.u.t.terfly through the growth of the imaginal buds.

_The Change to the b.u.t.terfly_ (_See plate, pages 32-33._)

There is probably no phenomenon in the world of living creatures which has attracted more attention than the change of the chrysalis into the b.u.t.terfly. It is not strange that this is so. We see upon a tree or shrub or wall an inert, apparently lifeless object, having no definite form with which we can compare it with other things, having neither eyes nor ears nor wings nor legs--an object apparently of as little interest as a lifeless piece of rock. A few minutes later we behold it again and note with astonishment that this apparently inanimate being has been suddenly transformed into the most ethereal of the creatures of earth, with an exquisite beauty that cannot fail to attract admiration, with wings of most delicate structure for flying through the air, with eyes of a thousand facets, with organs of smell that baffle the ingenuity of man to explain, with vibrant antennae, and a slender tongue adapted to feeding upon the nectar of flowers--the most ambrosial of natural food. So it is not strange that this emergence of a b.u.t.terfly has long been the theme both of poets and theologians and that it attracts the admiring attention of childhood, youth, and age.

Fortunately, this change from chrysalis to b.u.t.terfly may readily be observed by any one who will take a little trouble to rear the caterpillars or to watch chrysalids found outdoors. The precise method of eclosion, as we call this new kind of "hatching," varies somewhat with different species but in general the process is similar in all.

Those chrysalids which have a light colored outer skin are especially desirable if we would watch this process. One can see through the semi-transparent membrane the developing b.u.t.terfly within, until finally, just before it is ready to break out, the markings of the wings and body show distinctly. If at this time the chrysalis is placed in the sunshine it is likely to come out at once, so that you can observe it readily. It usually breaks apart over the head and the newly released legs quickly grasp hold of the empty skin as well as of the support to which it is attached. It then hangs downward with a very large abdomen and with the wings more or less crumpled up, but decidedly larger than when they were confined within the chrysalis.

The wings, however, soon begin to lengthen as they are stretched out, probably through the filling of the s.p.a.ce by the body juices.

Commonly, the hind pair of wings become full size before the front ones. In a short time the wings attain their full size, the abdomen becomes smaller, through the discharge of a liquid called meconium, and the b.u.t.terfly is likely to walk a few steps to a better position where it will rest quietly for an hour or two while body and wing tissues harden. After this it is likely to fly away to lead the free life of a b.u.t.terfly. (_See plate, page 16._)