Part 2

I. Head. 1, antenna; 2, eye; 3, proboscis; 4, palpus; cl. clypeus; o, occiput.

II. Thorax. 5, prothoracic leg; 6, mesothoracic leg; 7, metathoracic leg; e, e, e, episterna; c, c, c, coxæ; tr., tr., trochanters of last two legs; f, f, femora of do.; s, s, s, scuta of first, second, and third segments of thorax.

III. Abdomen. 1-9 segments; sp., sp., spiracles (after Burgess).

Fig. d. Head and legs of Œneis semidea, showing aborted front leg.

Fig. e. Palpus of Argynnis aphrodite.

Fig. f. Leg of Argynnis idalia. 1, coxa; 2, trochanter; 3, femur; 4, tibia; 5, tarsus.

Fig. g. Knobbed antenna of Argynnis idalia.

Fig. h. Clubbed antenna of Basilarchia astyanax.

Fig. i. Hooked antenna of Amblyscirtes vialis.

The subkingdom of the Arthropoda is divided into six classes, one of which consists of the Insecta (insects). It is estimated that there are three and a half millions of species of insects upon the globe, not to speak of the vast number of species which are now extinct, and known only by their fossil remains.

The Class Insecta is subdivided into many Orders. To attempt even to briefly speak of all these orders would take more space than the publisher has allotted to the author, and it is enough to say that butterflies belong to the order Lepidoptera. The lepidoptera are divided into two Suborders: the Rhopalocera, or Butterflies, and the Heterocera, or Moths. Both are characterized by having scaly wings, hence the name, which is derived from the Greek words λεπὶς (lepis) meaning scale, and πτερὸν (pteron) meaning wing. Lepidoptera are “scale-winged insects.” Any one who has ever handled a butterfly or moth, must have noticed upon his fingers a dust-like substance, rubbed off from the wings of the captured insect. Upon examining this substance under a microscope it is seen to be composed of minute scales (see Plate A, Fig. a), and upon looking at the wing of a butterfly under a magnifying glass it is seen to be covered with such scales, arranged somewhat as the scales upon the sides of a fish, or as the shingles upon the roof of a house (see Plate A, Fig. b).

Butterflies are mainly diurnal in their habits, preferring the sunshine. Moths on the other hand are nocturnal, and fly in the dusk, or after dark. Butterflies are therefore often called diurnal lepidoptera, and moths are spoken of as nocturnal lepidoptera. There are, however, a few butterflies which fly at dusk, and there are many moths which are diurnal in their habits. Such moths are generally gay in color, and for the most part inhabit tropical countries, although we have a few such species in the United States. Ordinarily the best way to distinguish between butterflies and moths is by examining their antennæ, or “feelers,” as they are sometimes incorrectly called. In the case of butterflies the antennæ are thread-like, terminating in a small knob-like, or club-like enlargement. It is this fact which has led naturalists to call them Rhopalocera. The word is derived from the Greek nouns ῥώπαλον (rhopalon) meaning a club, and κέρας (keras) a horn. Butterflies are lepidoptera having at the end of their antennæ clubs, which are sometimes short, long, or hooked (see Plate A, Figs. g, h, i.) The forms assumed by the antennæ of moths are very various. The moths are therefore known as Heterocera, the word being compounded from the Greek adjective ἕτερος (all sorts) and the noun κέρας (keras) a horn. Moths are lepidoptera having all sorts of antennæ, except such as are club-shaped at their ends. However there is no rule without its exceptions, and there are a few rare moths in tropical lands which have club-shaped antennæ like butterflies, but none of these occur in the region with which this book deals.

THE ANATOMY OF BUTTERFLIES

The body of a butterfly consists of the head, the thorax, and the abdomen (see Plate A, Fig. c).

The head carries two relatively large eyes, one on either side. The eyes of insects are compound, and if examined under a microscope are seen to have a multitude of minute facets, which serve to gather the light from all directions, so that butterflies can look forward and backward, upward and downward, as well as outward, all at one time. Between the eyes on the upper part of the head arise the antennæ, of which we have already spoken. The precise function of these organs in insects has been the subject of much discussion. Supposed by some to be ears, by others to be the seat of the sense of smell, by others to combine within themselves these two senses, and by still others to represent a sense which is not possessed by vertebrate animals, their use in the life of insects is not yet clearly understood. The weight of evidence seems to be in favor of the view that they are organs of smell, and it is now quite firmly established by experiment that the organs of hearing in insects are represented by certain pores and openings on their legs. In front between the eyes and below the antennæ are two little organs, each composed of three joints, which are known as the labial palpi (see Plate A, Fig. e). Between these, coiled up like a watch-spring, is the proboscis, with which the butterfly sucks up the nectar from flowers or drinks water from moist places (see Plate A, Figs. c and d). We have not the space in this little manual to go more deeply into the anatomy of these organs, but enough has been said to enable the beginner to recognize the various parts. The student realizes that the head in general supports the principal organs of sense and the proboscis, or mouth.

The thorax carries the organs of locomotion, which consist of four wings and six feet. The thorax is made up of three segments, or rings, the foremost of which is called the prothorax, the next the mesothorax, and the hindmost the metathorax. The subdivisions of the thorax are not easily distinguishable by examining the body of a butterfly even under a microscope, because the bodies of butterflies are generally heavily clothed with hairs and scales. In order to clearly make out the subdivisions, which we are considering, it is necessary to take a specimen and denude it of its scales and hairs, and even dissect it under a glass. The correctness of the foregoing statements then becomes apparent.

The legs of butterflies are arranged in three pairs, the foremost of which are known as prothoracic, being attached to the prothorax; the second pair are called mesothoracic, springing, as they do, from the middle segment of the thorax; and the last are styled metathoracic legs, rising from the hindmost segment of the chest (see Plate A, Fig. c). It should be noted here that in the great family of the Nymphalidæ, or “Brush-footed Butterflies,” in both sexes the anterior, or prothoracic pair of legs, are not fully developed, being aborted (see Plate A, Fig. d) and therefore do not serve for walking; and that in the families of the Erycinidæ, or “Metal-marks,” and the Lycænidæ, or “Blues and Coppers,” the females have six legs adapted to walking, while the males possess only four ambulatory legs, the front pair being in the latter sex aborted in these families, as in the Nymphalidæ. The legs of butterflies, like those of all other insects, consist of five parts (see Plate A, Fig. f) the first of which, nearest the body, is called the coxa, with which articulates a small ring-like piece, known as the trochanter. To the trochanter is attached the femur, and united with the latter, forming an angle with it, is the tibia. The last division of the leg is the tarsus, or foot, composed of a series of joints, to the last of which is attached a pair of claws, which in butterflies are generally rather minute, though in other orders of insects these claws are sometimes long and powerful, this being especially true of some beetles. The prothoracic legs of the Nymphalidæ and of the males of the Erycinidæ and Lycænidæ have lost the use of the tarsus, only retaining it in feeble form, and the tibia has undergone modification. In many of the Nymphalidæ the tibia is densely clothed with long hairs, giving this part of the leg the appearance of a brush, whence the name “Brush-footed Butterflies” (see Plate A, Fig. d). The tibiæ are often armed with more or less strongly developed spines.

The most striking parts of butterflies are their wings, which in proportion to the size of their bodies are usually very large, and which are remarkable for the beauty of the colors and the markings which they display both on the upper and on the under side.

The wings consist of a framework of horny tubes which are in reality double, the inner tube being filled with air, the outer tube with blood. The blood of insects is not, like that of vertebrates, red in color. It is almost colorless, or at most slightly stained with yellow. The circulation of the blood in the outer wall of the wing-tubes takes place most freely during the brief period in which the insect is expanding its wings after emergence from the chrysalis, concerning which we shall have more to say elsewhere. After the wings of the butterfly have become fully expanded, the circulation of the blood in the wings ceases almost entirely. The horny tubes, which compose the framework of the wings of butterflies, support between them a delicate membrane, to which upon both the upper and lower sides are attached the scales. The two fore wings are more or less triangular in outline; the hind wings are also subtriangular, but are generally more or less rounded on the outer margin, and in numerous forms are provided with tails or tail-like prolongations.

Inasmuch as in describing butterflies authors generally devote a good deal of attention to the markings of the wings, it is important for the student to become acquainted with the terms employed in designating the different parts of the wings (see Plate B, Fig. 10). That part of the wing which is nearest to the thorax, is called the base; the middle third of the wing is known as the median or discal area; the outer third as the external or limbal area. The anterior margin of the wing is called the costal margin; the outer edge is styled the external margin; the inner edge is known as the inner margin. The tip of the front wing is called the apex, which may be rounded, acute, falcate (sickle-shaped), or square (see Plate B, Figs. 1-4). The angle formed by the outer margin of the front wing with the inner margin is commonly known as the outer angle. The corresponding angle on the hind wing is known as the anal angle, and the point of the hind wing, which corresponds with the tip or apex of the fore wing, is designated as the external angle. The margins of wings may have different styles of outline, and are spoken of as entire, crenulate, scalloped, waved, lobed, or tailed (see Plate B, Figs. 5-8).

A knowledge of the veins which form the framework of the wings is important, because authors have frequently established genera upon the basis of the wing structure. It is desirable on this account to understand the nomenclature which has been applied to the veins. This nomenclature is somewhat variant, different writers having employed different terms to designate the same vein. In what follows the writer has adopted the designations which are most current, and which are generally accepted by authors. The best understanding of this matter is to be derived from the attentive study of the diagrams given on Plate B, Figs. 9 and 10. The veins in both the fore and hind wings of butterflies may be divided into simple and compound veins. In the fore wing the simple veins are the costal, the radials, the submedian, and the internal; in the hind wing they are the costal, the subcostal, the radials, the submedian, and the internal. The costal vein in the hind wing is, however, generally provided near the base with a short ascending branch, which is known as the precostal vein. In addition to the simple veins there are in the fore wing two branching veins, one immediately following the costal, known as the subcostal, and the other preceding the submedian, known as the median. The branches of these compound veins are known as nervules. The median vein always has three nervules. The nervules of the subcostal veins branch upwardly and outwardly toward the costal margin and the apex of the fore wing. There are always from four to five subcostal nervules, variously arranged. In the hind wing the subcostal is simple. The median vein in the hind wing has three nervules, as in the fore wing. In both wings between the subcostal and the median veins toward the base is enclosed the cell, which may be either closed or wholly or partially open at its outer extremity. The veinlets which close the cell are known as the discocellular veins, of which there are normally three. From the point of union of these discocellular veins go forth the radials, known respectively as upper and lower, though the upper radial in many genera is emitted from the lower margin of the subcostal vein.

EXPLANATION OF PLATE B

Fig. 1. Angulated or acuminate apex of fore wing (Grapta).

Fig. 2. Falcate apex of fore wing (Pyrrhanæa).

Fig. 3. Square apex of fore wing (Smyrna).

Fig. 4. Rounded apex of fore wing (Euptoieta).

Fig. 5. Hind wing rounded at outer angle, twice-tailed (Thecla).

Fig. 6. Hind wing crenulate, tailed, lobed at anal angle (Papilio).