The Butterfly Book. W. J. Holland

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СКАЧАТЬ the most part with the power of flight, and capable of reproducing their kind. All of this has been to some extent already elucidated in the first chapter of the present volume, but it may be well to remind the reader of these facts at this point.

       Fig. 76.—Antennæ of butterflies.

A question which is frequently asked by those who are not familiar with the subject relates to the manner in which it is possible to distinguish between moths and butterflies. A partial answer can be made in the light of the habits of the two classes of lepidoptera. Butterflies are diurnal in their habits, flying between sunrise and dusk, and very rarely taking the wing at night. This habit is so universal that these insects are frequently called by entomologists "the diurnal lepidoptera," or are simply spoken of as "diurnals." It is, however, true that many species of moths are also diurnal in their habits, though the great majority of them are nocturnal, or crepuscular, that is, flying at the dusk of the evening, or in the twilight of the early morning. Upon the basis of mere habit, then, we are able only to obtain a partial clue to the distinction between the two suborders. A more definite distinction is based upon structure, and specifically upon the structure of the antennæ. Butterflies have long, thread-like antennæ, provided with a swelling at the extremity, giving them a somewhat club-shaped appearance (Fig. 76). This form of antennæ is very unusual among the moths, and only occurs in a few rare genera, found in tropical countries, which seem to represent connecting-links between the butterflies and the moths. All the true moths which are found within the limits of the United States and Canada have antennæ which are not club-shaped, but are of various other forms. Some moths have thread-like antennæ tapering to a fine point; others have feather-shaped antennæ; others still have antennæ which are prismatic in form, and provided with a little hook, or spur, at the end; and there are many modifications and variations of these forms. The club-shaped form of the antennæ of butterflies has led naturalists to call them Rhopalocera, as has been already explained in speaking of this subject on page 17. Moths are called Heterocera. The word Heterocera is compounded of the Greek word (ἑτερον), meaning other, and the Greek word (κερασ), meaning a horn. They are lepidoptera which have antennæ which are other than club-shaped. Besides the distinctions which exist in the matter of the form of the antennæ, there are distinctions in the veins of the wings, and in the manner of carrying them when at rest or in flight, which are quite characteristic of the two groups; but all of these things the attentive student will quickly learn for himself by observation.

       Fig. 77.—Antennæ of moths.

      Scientific Arrangement.—Having thus cast a passing glance at the differences which exist between moths and butterflies, we take up the question of the subdivision of the butterflies into natural groups. Various systems of arranging butterflies have been suggested from time to time by learned writers, and for a knowledge of these systems the student may consult works which treat of them at length. It is sufficient for beginners, for whom this book is principally written, to observe that in modern science, for purposes of convenience, as well as from regard for essential truth, all individuals are looked upon as belonging to a species. A species includes all those individuals, which have a common ancestry, and are so related in form and structure as to be manifestly separable from all other similarly constituted assemblages of individuals. For instance, all the large cats having a tawny skin, and in the male a shaggy mane, constitute a species, which we call the lion; the eagles in the eastern United States, which in adult plumage have a snow-white head and neck and a white tail, constitute a species, which we know as the "white-headed" or "bald-headed" eagle. Species may then be grouped together, and those which are manifestly closely related to one another are regarded as forming a natural assemblage of species, to which we give the name of a genus. For example, all the large cats, such as the lion, the tiger, the puma, and the jaguar, are grouped together by naturalists, and form a genus to which is given the Latin name Felis, meaning cat. The name of the genus always comes before that of the species. Thus the tiger is spoken of scientifically as Felis tigris. The genera which are closely related to one another may again be assembled as subfamilies; and the subfamilies may be united to form families. For instance, all the various genera of cats form a family, which is known as the Felidæ, or the Cat Family. A group of families constitutes a suborder or an order. The cats belong to the Carnivora, or order of flesh-eating animals.

      In zoölogy family names are formed with the termination -idæ, and subfamily names with the termination-inæ.

      Everything just said in regard to the classification of the higher animals applies likewise to butterflies. Let us take as an illustration the common milkweed butterfly. Linnæus for a fanciful reason gave this insect the name Plexippus. This is its specific name, by which it is distinguished from all other butterflies. It belongs to the genus Anosia. The genus Anosia is one of the genera which make up the subfamily of the Euplœinæ. The Euplœinæ belong to the great family of the Nymphalidæ. The Nymphalidæ are a part of the suborder of the Rhopalocera, or true butterflies, one of the two great subdivisions of the order Lepidoptera, belonging to the great class Insecta, the highest class in the subkingdom of the Arthropoda. The matter may be represented in a tabular form, in the reverse order from that which has been given:

      Subkingdom, Arthropoda. Class, Insecta. Order, Lepidoptera. Suborder, Rhopalocera. Family, Nymphalidæ. Subfamily, Euplœinæ. Genus, Anosia. Species, Plexippus (Milkweed Butterfly).

      

      Varieties.—A still further subdivision is in some cases recognized as necessary. A species which has a wide range over an extensive territory may vary in different parts of the territory within which it is found. The butterflies of certain common European species are found also in Japan and Corea, but, as a rule, they are much larger in the latter countries than they are in Europe, and in some cases more brightly colored. Naturalists have therefore distinguished the Asiatic from the European form by giving the former what is known as a varietal name. Similar differences occur among butterflies on the continent of North America. The great yellow and black-barred swallowtail butterfly known as Papilio turnus occurs from Florida to Alaska. But the specimens from Alaska are always much smaller than those from other regions, and have a very dwarfed appearance. This dwarfed form constitutes what is known as a local race, or variety, of the species. The members of a species which occur upon an island frequently differ in marked respects from specimens which occur upon the adjacent mainland. By insulation and the process of through-breeding the creature has come to acquire characteristics which separate it in a marked degree from the closely allied continental form, and yet not sufficiently to justify us in treating it as a distinct species. It represents what is known as an insular race, or variety, and we give it therefore a varietal name. Naturalists also distinguish between seasonal, dimorphic, melanic, and albino forms. Names descriptive or designatory of these forms are frequently applied to them. All of this will become plainer in the course of the study of the succeeding pages, and in the effort to classify specimens which the student will make.

      Sex.—The designation of the sex is important in the case of all well-ordered collections of zoölogical specimens. As a measure of convenience, the male is usually indicated by the sign of Mars, ♂, while the female is indicated by the sign of Venus, ♁. The inscription, "Argynnis Diana, ♂," therefore means that the specimen is a male of Argynnis Diana, and the inscription, "Argynnis Diana, ♁," means that the specimen is a female of the same species. These signs are invariably employed by naturalists to mark the sexes.

      The Division of Butterflies into Families.—Without attempting to go deeply into questions of classification at the present point, it will be well for us to note the subdivisions which have been made into the larger groups, known СКАЧАТЬ