The New International Encyclopædia/Butterflies and Moths

BUTTERFLIES AND MOTHS (the name is probably due to the popular belief that it steals butter and milk; or it may refer to the color of the excrement; cf. M. Dutch boterschijte, schete). Insects of the order Lepidoptera which are not separable by any distinct line of structural characters. (See .) They agree in essentials and their popular separation is a practical rather than a natural one. Perhaps the nearest we may come to a definite distinction is to call butterflies all those Lepidoptera whose pairs of wings are never fastened together in flight; and call moths all those whose wings are so united.

“The popular division of Lepidoptera into ‘butterflies’ (Rhopalocera) and ‘moths’ (Heterocera) is quite unscientific, the butterflies being more nearly related to the higher moths than these to the lower moths. It has been proposed to separate the three lowest families which have. . . a jugum on each fore wing, as Jugatæ, from all other Lepidoptera—Frenatæ; also to divide the families with incomplete pupæ (Incompletæ) from those with obtect pupæ (Obtectæ); also to separate the lowest family on account of the structure of the first maxillæ as a suborder (Laciniata) distinct from all other families (Haustellata). On the whole, it is better not to adopt any division of the Lepidoptera between the order and the family.” (G. H. Carpenter, Insects, New York, 1899.)

Butterflies, as a rule, go abroad in the daytime, seeking no concealment, and are brightly colored, while moths more usually fly in the twilight or at night, and are subdued in hue. Butterflies are distinguished by the terminal knob (or occasionally hook) of the antennæ, whence the common group-name Rhopalocera, while the antennæ of moths (Heterocera) are usually otherwise in form, often filiform or feathery. Butterflies have the habit of holding the wings in a vertical position over the back when at rest, while moths usually keep them flat.

Of the Lepidoptera represented in North America, the following families may be called butterflies: Hesperiidæ, Lycænidæ, Lemoniidæ, Nymphalidæ, and Papilionidæ; and all the rest moths, among which the Pterophoridæ, Tineidæ, Tortricidæ, Pyralidæ, Geometridæ, Noctuidæ, Bombycidæ, Zygænidæ, Ægeriidæ, and Sphingidæ

are most important. Other families of both sorts belong only to South America or the Old World.

. The head in this group is distinct from the thorax, clothed with hairs, and bears large, compound eyes, and moths have also simple eyes (ocelli). The antennæ are always present, and important not only as feelers, but as organs of hearing and smell (see ), the latter service being probably a very important one in this group. These antennæ take various shapes. Among butterflies they are thickened at the end, sometimes into a rounded club, but more often into a spindle-shape terminating in a bent point. Of the moths "some 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 shape, or at least the size, usually varies between the sexes, being larger in the male than in the female—a fact connected with his duty to search for her, and especially observable in moths. The same may be said of the eyes, which, in the nocturnal species, cover the whole side of the head and have an enormous number of facets—27,000, it is said, in some hawk-moths.

The mouth in the Lepidoptera is modified into a sucking-organ, enabling this insect to feed on the nectar of flowers and the sap of trees and plants. The mandibles are rudimentary or absent, and the maxillæ, by a very extraordinary development and modification, are formed into a sucking-tube, called the proboscis, which, when not in use, is coiled up between two forward-projecting organs, the labial palpi. It is “composed of three distinct hollow tubes, soldered to each other along their inner margins,” and “has much the appearance of a double-barreled gun, with a third tube lying below.” Nutrition is imbibed through the lower or central tube, by a regular pumping, produced by the alternate muscular pinching and loosening of a bulb-like arrangement in the head; and the other tubes admit air. In some of the sphinx-moths the proboscis may be ten inches long, and in others its tip is armed with spines which serve to break or cut the surface of fruits, the juice of which is sucked up.

Wings.—The thorax bears the legs and wings. The former are weak and are merely used as organs of support when the insect is at rest, and the front pair of legs may be short or rudimentary, as is the case in Vanessa. The four membranous wings are usually large in comparison with the size of the body; expanse of wing and strength of flight, however, are not exactly correlated, for some of the hawk-moths with proportionately small wings are the most enduring flyers, yet the large-winged forms probably fly with less exertion. In actual size lepidopterans vary from almost microscopic species, hiding in the moss, to tropical monarchs 12 inches in expanse. These transparent membranes are supported by a framework radiating from the thoracic joints, which consist of double horny tubes (veins or ‘nerves’ and nervules) one within the other, the inner being filled with air and the outer with nutritive fluids. “These ‘nerves,’ as custom will persist in terming them, in the butterflies, take a bow-like or ellipsoidal sweep from the base of the wing, forming what is the ‘discoidal cell,’ whence there branch off to the edges a

series of horizontal, almost parallel, slightly divergent nervules. On the position of these the identification of species is most securely based. . . . In the moths, on the other hand, the discoidal cell is less conspicuous.” The names of the parts of the wing, and of its veins and nervules, used by entomologists in their descriptions of species, are given in the accompanying illustrations. To further increase the power of the pinions, the pair on each side are made to act as one. This adjustment is effected either by an overlapping of the hind wing by the front wing (butterflies or some of the larger moths) or the posterior wing possesses a ‘frenulum.’ composed of one or more bristles, which fits into a ‘retinaculum,’ a membranous flap or a bunch of scales on the anterior wing (other moths). According to Hampson, “the form of the frenulum is of use in determining sex, as in the males of all the forms that possess it it consists of hairs firmly soldered together so as to form a single bristle, while in nearly all females it consists of three or more bristles, separate and shorter than that of the male.”

Scales.—The wings of all Lepidoptera, as the word implies, are clothed more or less completely with scales, which are modified hairs—hairs that are very short and much widened; and every gradation may be found, in a species like Ithomyia, between the hairs on the body and wings and the scales. They are like small chitinous bags with the sides pressed together, and each one has on its proximal end a short stalk which fits into a cavity of the wing-membrane. They are of various shapes, notched on the posterior margin, striated, etc., and “the males of many species have peculiarly shaped scales arranged in tufts and folds, which are called ‘androconia,’ and are useful in microscopically determining species.” The scales are in rows, and overlap much as do the scales on a fish or the shingles on the roof of a house. They rub off easily, and entomologists know how to remove them without serious injury; but when taken from a living insect they diminish or destroy its ability to fly. They number hundreds of thousands, and their use is to strengthen the membranous wings, and when they overlap the wing-membranes at the edges to a considerable extent, as occurs in some cases, they also increase the wing-area. Another use is to bear the colors of the wings, for when the scales are removed the color is gone. This color is due either to pigment contained within the scale or its walls, or to the fine striations on the upper surface which give rise to metallic ‘interference colors.’ Both albinism and melanism occur. The pigments are perhaps in the nature of biliary excretions, such as urates from nitrogenous matter and melanins from carbonaceous matter.

Distinctions of Sex.—The abdomen is composed of segments, nine for the female and ten for the male, and contains the viscera, and the lateral spiracles by which air is admitted to the respiratory system. It is shorter in most butterflies than the hinder wings; and in most moths is tufted along the dorsal line and on the end. The terminal segment has various appendages, and contains the sexual organs of both sexes. There is often a very striking difference in size, color, and form between the females, especially among the butterflies, where procreation may be the sole duty of the imago during its brief

existence. In case there are several broods of butterflies in a season, each brood may have its characteristic coloration. Our Ajax butterfly is three-brooded, and before the facts of its life-history were known, each brood had been given a specific name. By artificially varying the temperature or moisture, any or all the seasonal forms may be produced at will from one and the same laying of eggs. The males, which are usually more gayly decorated than the females and exceed them in number, are continually in search, about the food-plants, of mates, who exert a far-reaching attracting power. Collectors utilize this instinct: having caught a female they expose it in a cage and soon are likely to find several males flocking about it. Under certain circumstances eggs may be laid by an unfertilized female (for which see and ). Adherents of the doctrine of sexual selection believe the female exercises a choice among these assembled suitors, selecting for her partner the best, according to the standard of the species, and so maintaining the high quality of the race. A single impregnation is sufficient, and the impregnated females soon begin to lay eggs, having accomplished which, they die, in the great majority of cases, the exceptions being those which are double-brooded, or (a very few) where the adults largely survive the winter.

. A few butterflies, such as the mourning-cloak, are able to endure in a state of torpidity the winters of the north. A large number winter over as pupæ, and others, like the brown and black Isabella caterpillar, as well-grown caterpillars. Others hatch out only in time to go into winter quarters. Many winter over as eggs, and not a few in two different stages, the latter having a double chance of surviving. It has been established by at least one set of careful observations that the cabbage butterfly (see ) of Southern Europe migrates or flies in a general southerly direction in the fall and northerly in the spring. In the United States the milkweed butterfly (q.v.) sometimes so migrates in enormous swarms. Such migrations are even more common in the tropics. In his work on Ceylon, Sir James Tennent writes of “the extraordinary sight of flights of these delicate creatures, generally of white or pale yellow hue, apparently miles in breadth, and of such prodigious extension as to occupy hours and even days uninterruptedly in their passage.” These migrations are at times occasioned by lack of food-plants on which to deposit eggs. In other cases we know they are seasonal. By going south the butterflies find a climate in which they are able to winter.

. The eggs of all Lepidoptera are laid on or near the food-plant, that is, the plant upon which the young must feed. In number they vary from less than one hundred to several thousand, and are deposited continuously and rapidly, as a rule. They may be placed singly, as is common among butterflies, or, as is more usual among moths, in clusters or masses, adhering to their support and perhaps to each other by a glutinous coating; while some moths prepare a sort of nest of hairs plucked from their bodies upon and within which the eggs rest, or otherwise protect them from observation or the weather, especially those destined to last through a northern winter

or tropical season of drouth. Their membranous shells take various forms, and are often exceedingly beautiful when seen through the microscope. “Some,” says Holland, “are spherical, others hemispherical, conical, and cylindrical. Some are barrel-shaped, others have the shape of a cheese, and still others have the form of a turban. Many of them are angled, some depressed at the ends. Their surface is variously ornamented. Sometimes they are ribbed. . . [and] between these ribs there is frequently found a fine network of raised lines variously arranged. . . . As there is great variety in the form of the eggs, so also is there great variety in their color. Brown, blue, green, red, and yellow eggs occur. Greenish or greenish white are common tints. The eggs are often ornamented with dots and lines of darker color. . . . Fertile eggs, a few days after they have been deposited, frequently undergo a change of color, and it is often possible with a magnifying-glass to see through the thin shell the form of the embryo which is being developed within the egg.” The eggs may hatch in a few days or only after mouths, for numerous species pass the winter or the dry season in the egg. The larva which is born in the egg, and which escapes by an opening, of curious structure, at the upper end of the shell, called the micropyle, is known as a caterpillar.

This larva, or ‘caterpillar,’ is a worm-like creature, and takes a form, color, etc., characteristic of its group and species. The term properly is restricted to lepidopterous larvæ alone, though sometimes applied to other larvæ, as those of the saw-flies. The head of the caterpillar is conspicuous, often large, and composed of horny (chitinous) material, taking various shapes. It is provided with six simple eyes (ocelli), usually to be seen only with the aid of a lens, which are either just above each mandible, or on each side of the head; there are two rudimentary antennæ. The mouth is adapted for tearing, cutting, and masticating the substances on which the caterpillar is destined to feed, which are very various in the different species, although in all extremely different from the food of the perfect insect; it is provided with strong upper and lower jaws; a labium, or lower lip; and four palpi. In the mouth (labium) also is situated the spinneret of those species which, when they change into the chrysalis, envelop themselves in silken cocoons. (See .) The first three segments of the body are each furnished with a pair of short legs, which are hard, scaly, and clawed, and represent the six legs of the perfect insect; some of the remaining segments are also furnished with short feet (prolegs), varying in all from four to 10 in number, the last pair situated at the posterior extremity of the body; but these are membranous or fleshy, and armed at their extremity with minute hooks. Those caterpillars in which the prolegs (which are shed in the last molt) are pretty equally distributed along the body, move by a sort of regular crawling motion; but those which have only four such feet, near the posterior extremity, move by stretching the body out to its full length, taking hold by their fore feet, and then bending the body into an arch, thus bringing the hind feet forward, when the body is stretched out again for a new step, and so on; this last is the method of progression of the geometrid moths, called

loopers, inch-worms, or measurers. The larva appears to guide itself by its feelers (palpi). The heads of many caterpillars also have defensive spines, or arrangements for emitting noisome liquids or odors, to be referred to later. The body of the caterpillar contains nearly all the organs of the adult butterfly or moth. Respiration goes on through nine spiracles on each side, two on each ring, except the second, third, and last. There are no external traces of sexual organs, but there arise, during this stage, the ‘imaginal disks,’ which develop into the wings and legs of the adult insect. These rudiments of wings exist even in very young caterpillars as a thickening and bagging in of the hypodermis. Into this bag, trachea and blood make their way. Just how these internal wings reach the outside is not known; probably by the destruction of the outside hypodermis. If the wing-membrane breaks during development, so that the blood or hæmolymph exudes, the injured wing will lie smaller or deformed. Sometimes the wings fail to expand properly because they dry too soon, and a wet sponge under a bell-jar, with transforming Lepidoptera, will aid in the production of perfect specimens.

Feeding Habits and Mischief.—Caterpillars find themselves at birth in contact with proper food, and begin at once to devour it, and to obey certain other instincts necessary to their life and prosperity. This is the stage in which the butterfly or moth gets most of its nourishment and growth, none taking food in the next or pupal stage, and many not feeding at all as imagos. The great majority are vegetable-eaters, many being limited to a particular kind of plant, or to a few nearly allied plants. Some feed on flowers, some on seeds, some on roots, and some even on the woody portions of stems; some on wool, hides, furs, and other animal substances; a few on lard, and other kinds of fat. Some feed in the dark, and some in the light. Some kinds seem to eat almost incessantly, but most of them have alternate periods of ravenousness and quiescence. As many of the favorite food-plants have been cultivated by civilized man, and other substances eaten by these creatures have been made use of by him, he has multiplied by his operations the supply and consequently the numbers of certain species until they have become pests, destructive of his work and profits. It is in the caterpillar stage that almost all the destructiveness of the lepidoptera is accomplished. On certain years they succeed in denuding whole forests or many fields. The cutworm, the army-worm, and the cotton-worm are well-known pests. Their voracity is remarkable. According to Trouvelot, when a Polyphemus caterpillar hatches, it weighs one-twentieth of a grain, and when it is 50 days old, it weighs 207 grains, and has consumed 120 oak-leaves, weighing three-fourths of a pound. “So the food taken by a single silkworm in 56 days equals in weight 86,000 times the primitive weight of the worm. What a destruction of leaves this single species of insects could make if only a one-hundredth part of the eggs laid came to maturity! A few years would be sufficient for the propagation of a number large enough to devour all the leaves of our forests.”

Taken as a whole, caterpillars are economically so injurious that were it not for the great depletion of their numbers by their multitudinous

foes, they would soon destroy the vegetable kingdom. They injure, or even kill, shrubs and trees, as well as all sorts of garden vegetables. They eat woolen stuffs of all kinds and furs. To offset all their destructiveness, they offer little save silk that is, at present at least, known to be useful to man. There are a few species that are helpful to vegetation, such as the Lycænidæ, which feed on plant-lice and scale-insects. One such species (Feniseca Tarquinius) occurs in the United States. A few forms are aquatic and feed on plants under water.

Self-Protection in Caterpillars.—The skin of some caterpillars is naked, that of others is covered with hairs, spines, or tubercles. Most are solitary, but some make for themselves nests or tents of silk, under which they dwell in societies, protected from the inclemency of the weather. Many construct cases or sheaths by agglutinating various substances together, as the caterpillar of the common clothes-moth. Some roll together leaves, and fix them by threads, so forming a dwelling for themselves; and a few burrow and excavate galleries in the substance of leaves or in the pith of plants. Most of them are in color brown or green, while those hidden in galleries are whitish; but many carry gaudy colors and numerous ornamental or strange protuberances. All these characteristics are connected with Nature's effort to protect them from their enemies. Alfred Russel Wallace has made clear the fatality to caterpillars of even slight wounds, for “a slight wound entails great loss of blood, while a modest injury must prove fatal.” Therefore devices that enable caterpillars to escape the notice or the attacks of enemies are very useful to them. Many caterpillars possess a disagreeable smell, or a nauseous taste, or both. Thus, those of the swallow-tailed butterflies “are provided with a bifurcate or forked organ, generally yellow in color, which is protruded from an opening in the skin back of the head, and which emits a powerful odor; this protrusive organ evidently exists only for the purposes of defense.” Most caterpillars resist an attack by hurling their bodies violently from side to side. Others assume startling attitudes, or have a surprising arrangement of color. These terrifying attitudes may accompany disagreeable tastes and so serve more vividly to impress upon the foe the unpleasant quality of the prey. Nevertheless, as Professor Poulton has stated, hungry animals may come to eat and like distasteful caterpillars. Certain caterpillars escape the enemy by resembling the color of the background, concerning which more is to be said elsewhere. Others, such as the geometrids or measuring worms, may combine with this protective coloration the capacity of attaching themselves by the hind end and stretching out in the air like a twig. This rigid attitude they may maintain for some time. Imitation may even be carried to the length of mimicking other kinds of animals. Thus the huge eye-spots, peculiar folds, and marks on the anterior end give some forms the appearance of snakes or other strong animals. The color of caterpillars is due to two sources: (1) Pigment gained from the food; (2) pigment inherent in the deep-lying tissues or skin. Most green caterpillars seem in some way to be colored by the chlorophyll of the food-plant. Yellow is derived mainly from xanthophyll of plants. Pigment derived from food-plants tends

gradually to give the caterpillar the coloration of the surroundings. See ;
 * etc.

Struggle for Existence.—Only a few out of the vast hosts of caterpillars ever reach maturity. Many are destroyed by cold, wet, drouth, or lack of food. Vast numbers fall prey to birds, reptiles, and mammals. Many others are caught by wasps and stored up as food for the young, or are captured by adult and larval predaceous beetles. Ichneumon flies deposit their eggs within great numbers of caterpillars, where they develop and eventually kill the caterpillar or pupa. Tachina-flies also lay their eggs on caterpillars and the larvæ are parasitic within them. In addition, caterpillars are subject to fungus and various other contagious diseases which are particularly fatal to the cultivated silkworm.

Molting.—Soon after the caterpillar begins to take food and increase in size, it is obliged to shed its skin, which has become too tight. To take its place, a larger, soft one is developed beneath the old one. This new skin becomes, in its turn, too tight and unelastic, and must be shed. A number of such moltings or eedyses take place before the embryo attains full size. These normally occur at regular intervals, and four or five molts complete the growth; but “in cases where caterpillars hibernate. . . a long interval necessarily elapses. Some Arctic species are known in which the development from the egg to the perfect insect covers a period of two or three years.” The manner in which the molting is effected is very interesting. When the necessity is felt, the caterpillar ceases feeding, attaches itself firmly to some object, and becomes quiet for a time. “The process begins with a splitting of the skin on the upper surface of the thorax; this is continued forward to the head, which opens along the sutures. The head and thorax of the new stage, or ‘instar’, are then worked out by an energetic wriggling motion of the insect, and the old skin is gradually stripped off from before backward, like the finger of a glove. In caterpillars it is known that a fluid, secreted by glands in the hypodermis, is present at molting-times between the new and the old skin, which it helps to separate.” (Carpenter.)

The caterpillar may be regarded as a recapitulation of one stage in the phylogenetic development, that is to say, in the evolution of the lepidopterous insect. It may indeed be said to reproduce a stage in the phylogeny of insects best represented to-day by Peripatus, a primitive and widely distributed genus that serves to connect arthropods with worms.

Pupation.—After a caterpillar has passed through the period of successive feedings and moltings which the economy of its species requires, it prepares to pass into the second larval stage and become a pupa, in which tough integuments cover the developing organs instead of soft skin. Pupæ may cover themselves with a case of silk or other materials, called a cocoon, or may remain naked, in which ease they are known as chrysalids (sing. chrysalis). The former is the custom among the moths—the latter among the butterflies. The insect in this stage is utterly helpless, and a cocoon serves as a protection. It is spun as the last act just before passing into the pupal stage, and is formed of silken threads, produced by the hardening of the fluid secreted by the spinning glands. These may be

wound round and round the larva, until the silken case thus made suffices; or they may form merely the lining of an earthen cell (for many species pupate under ground), or they may serve to bind into the cocoon their own hairs, chips of wood, or other materials, or to tie down rolled leaves, or form a web-like network hung like a bag or a hammock from some support, or making a fuzzy mass in some crevice or among leaves and twigs. When the work of spinning the silk is once begun, it is carried on almost without cessation for several days. The forms of cocoons are various; when not concealed, they are usually of a tint that blends well with their surroundings, leaving them inconspicuous, while their material is calculated to resist the attacks of insect-eating birds and mammals, or of ichneumon-flies and other intending parasites.

Cocoons are mainly the work of moths, to which the term ‘pupa’ is now frequently restricted, for the butterflies pass their pupal stage incased in comparatively rigid integuments, which form a ‘chrysalis.’ They vary greatly in form, some being acorn-like, others very angular, etc., and most are obscure in tint, so as to be easily overlooked, but some are brilliant in color, usually of golden or metallic hues, whence the name chrysalis. Some butterfly chrysalids (Nymphalidæ) are simply suspended from the posterior end (Suspensi); those of others (Papilionidæ) are held in place by an additional strand or girdle of silk (Succincti). Within the chrysalis or cocoon is the immature butterfly or moth, and all the parts belonging to the future adult insect may be found by examination. Breathing goes on through air openings, and the parts steadily develop. “The pupæ of the vast majority of moths, of butterflies, and of two-winged flies have the limbs and wings not merely pressed close to the body, but immovably fixed thereto by a general hardening and fusion of the outer skin. Such pupæ are distinguished as ‘obtect.’ But although the limbs are incapable of motion, certain abdominal segments remain free, so that the hind body can be, to some extent, bent and turned about; and, by means of rows of spines on the abdominal segments, the pupa is, in many cases, enabled to work its way out of its shelter, when the time for the final change has arrived.” Such are styled ‘incomplete.’ The pupal stage may be of long or short duration. Many Lepidoptera pass the winter or the tropical dry season as pupæ. Some have several broods a year, and in such the pupal stage of the hibernating brood will last longer than that of the others.

The Imago.—When the pupa has arrived at maturity; its coverings split and allow the emergence of the ‘imago’ or perfect insect. “Hardly anything in the range of insect life,” remarks Dr. W. J. Holland, “is more interesting than the rapid development of the butterfly after its first emergence from the chrysalis. . . The imago, as it first emerges, is provided with small, flaccid wings, which, together with all the organs of sense, such as the antennæ, require for their complete development the injection into them of the vital fluids, which, upon first emergence, are largely contained in the cavities of the thorax and abdomen. Hanging pendant on a projecting twig, or clinging to the side of a rock, the insect remains, fanning its wings, while by the strong process of circulation, a rapid injection of the blood into the wings and other organs

takes place, accompanied by their expansion to normal proportions, in which they gradually attain to more or less rigidity. . . The body is robbed of its liquid contents in a large degree; the abdomen is shortened up; the chitinous rings which compose its external skeleton become set and hardened; the wings are expanded, and then the moment arrives when, on airy pinions, the creature that has lived a worm-like life for weeks and months, or which has been apparently sleeping the sleep of death in its cerements, soars aloft in the air, the companion of the sunlight and the breezes.”

It is impossible here to go into any description of butterflies and moths. Butterflies, as a rule, are more brilliant than moths, many of them, in the tropics, especially resplendent in metallic hues, rivaling those of the ‘eyes’ of peacock-plumes. Moths, on the contrary, are more usually dull of hue, and less given to appearing in open places, even when they fly by day, yet some are high-colored and beatitiful.

Both butterflies and moths, and their caterpillars, may resemble to some extent the shape of the object or the coloration of their background, or of other insects. Thus they illustrate most strikingly and copiously various phases of ‘mimicry’ and ‘protective coloring.’

Butterflies, like bees and many other insects, carry pollen from flower to flower, and hence aid greatly in the formation of seeds. See .

. Lepidoptera occur wherever plant-life suited to the nourishment of the caterpillars is present. They are sun-loving forms, and are most numerous in species in the tropics. However, in numbers of individuals, some of the temperate zone forms far outrank any of the others. Some species occur in the Arctic zone and on the tops of snow-clad mountains. Certain forms flourish in the far north, in Greenland, Labrador, and Iceland, or on tops of snow-capped mountains. Some species are restricted by temperature or food-plant to a very limited area, while others are practically of world-wide distribution. Widely distributed forms either feed on widely distributed plants, or can feed on a number of different food-plants.

The delicacy of the Lepidoptera has prevented their common preservation as fossils. The Tertiary rocks of the Western United States, and the rocks from the time of the British chalk down, have yielded remains of a few scattered species.

About 50,000 species of Lepidoptera are known, of which 6,000 occur in America north of Mexico. Of skippers there are two families—the large skippers, Megathymidæ, and the smaller skippers, Hesperiidæ. The butterflies include the Papilionidæ, Pieridæ, Lycænidæ, and Nymphalidæ, and all other families (over 40) belong to the moths.

. For general works, see bibliography under ; A. Hyatt and J. M. Arms, “Meaning of Metamorphosis,” Natural Science, VIII. (London, 1896); E. B. Poulton, “Neurology of Pupæ” in Transactions of the Linnæan Society (London, 1890); T. A. Chapman, “Pupæ of Moths,” in Transactions of the Entomological Society (London, 1893); and subsequently W. F. Kirby, Handbook to European Butterflies and Moths (with guide to literature of the order, 5 vols., London, 1895); S. H. Scudder, Butterflies of New England (3 vols., Cambridge, 1889); W. J. Holland, The Butterfly Book (New York, 1898);

G. H. French, Butterflies of the Eastern United States (Philadelphia, 1895); A. Weismann, New Experiments on the Seasonal Dimorphism of Lepidoptera, translated by W. E. Nicholson in Entomologist, January-August (London, 1896); Walker, British Museum Catologue of Lepidoptera (London, 1854-56); Herrich-Schaffer, Systematische Bearbeitung der Schmetterlinge von Europa (Regensburg, 1843-56); Doubleday and Westwood, Genera of Diurnal Lepidoiitera (London, 1846-62); H. J. Elwes, “The Distribution of Butterflies,” in Proceedings of the Entomological Society (London, 1894); A. S. Packard, Text-Book of Entymology (New York, 1898). For works relating to special families and species, see their names.