The bodies of butterflies and moths, like those of all other insects, consist of three distinct parts—the head, bearing the organs of sense; the thorax, the organs of locomotion; and the abdomen, the organs of generation. On the head are placed (1) the antennae, composed of numerous articulations, and supposed to be organs of hearing. They differ greatly in form among the Lepidoptera ; those of butterflies, however, agreeing generally in having their ends knobbed or clubbed, hence the term Rhopalocera (ρόπαλον, a club; κepaς, a horn), often applied to this group. The antennae of moths assume a great variety of forms—prismatic, serrate, pectinate, moniliform, and filiform,—and are often beautifully feathered, especially in the males, whose antennae arc usually ampler than those of the females; but in no case are they knobbed, as in the great majority of butterflies. Owing to this vaιiety iu the form of their antennae, moths have been termed l·leterocera (cτcpos, various; κepαs, a horn). In butterflies these organs are also straight, and stand out rigidly in front of the head, while in moths they are usually curved and can generally be folded back on the body. (2) The eyes in the Lepidoptera consist of two masses of hexagonal facets, placed one on each side of the head, and forming what are known as compound eyes. These contain in some cases no fewer than 16,000 facets each, while in many species a pair of ocelli, or simple eyes, are found concealed among the scales and placed between the compound organs. The hairy appearance of the eyes in many of the Nymphalidce is owing to the presence of minute hairs planted at the angles of the numerous facets. Compound eyes are not found among the larvae of butterflies and moths, but they are in most cases provided with six ocelli on each side of the head. (3) The mouth, the parts of which in insects are considered by comparative anatomists to be typically developed in the masticatory mouth of beetles (Coleoptera), assumes in butterflies and moths the suctorial form—the latter being merely a modification of the former; thus the mandibles, labium, and labrum, which are fully developed when the nature of the food renders mastication necessary, are in a rudimentary condition in the Lepidoptera, whose chief food is the nectar of flowers, while the maxillae, on the other hand, are enormously developed; being concave on their inner sides, these by approximating form a tube known as the proboscis or tongue. This when at rest is coiled up into a ball in front of the head, and is partly concealed by the palpi projecting on both sides. In the moths belonging to the family Bombycidoe, the organs of the mouth are rudimentary, so that these insects after entering upon the imago state are incapable of feeding.
The thorax bears the organs of locomotion, consisting of three pairs of legs and two pairs of wings. The former are covered with hairs and scales, and terminate in hooks modified to suit the habits of the various species. Butterflies use the legs almost entirely for resting, very rarely for walking, and in some groups, as the Nymphalidce, the front pair is rudimentary. The wings consist of a double layer of colourless membrane traversed by numerous nervures (Plate XXVII. fig. 1), and covered with minute scales implanted in the wing membrane by a short stalk, and placed together like tiles on a roof. The scales vary in form in different species and in different portions of the wings of the same species, while under a high power of the microscope they are seen to be minutely corrugated; and it is to these corrugations acting upon the colourless rays of light, and producing the phenomena of “interference,” that many of the loveliest butterflies owe the brilliancy of their wings. The splendour of those organs in the majority of butterflies, and in some moths, is sometimes equally shared by both sexes, but more usually the females are less conspicuously coloured than the males. This difference, amounting often to total dissimilarity, Darwin, in accordance with his descenttheory, attributes in great part to the action of sexual selection. “Several males,” he says, “may be seen pursuing the same female.” The latter he supposes selects the most gaily-coloured, and thus the plainer coloured males have been gradually eliminated; but there is no proof whatever that the female shows any such discrimination in selecting a mate, while many known facts seem to point in an opposite direction. Mr A. R. Wallace maintains, on the other hand, that the duller colours of the females have been acquired for protective purposes, the females requiring such protection more than the males owing to their generally slower flight, and to the fact that after imprégna-tion they take several days to deposit their eggs, during which the life of the male is of no further consequence to the perpetuation of the species. Whatever may be the true interpretation of this phenomenon, it is certain that many butterflies and moths of both sexes are so coloured as to be to a greater or less extent protected thereby. Many moths, which rest by day clinging to the trunks of trees, so exactly resemble in the colour of their upper wings the bark on which they rest as only to be distinguished on close examination; while many small species which habitually rest on leaves are often mistaken for the dropping3 of birds. The upper surfaces of the wings of butterflies are in almost all cases the more gaily coloured, and when at rest, these are raised perpendicularly over the back, so as only to expose the under surfaces, which are often dull coloured, and in some cases have been shown to be directly imitative of surrounding objects. The best example of this is to be found in the Malayan butterfly, Kallima paralekta, and its Indian ally, Kallima inachis, both brilliant and conspicuous insects on the wing, but which no sooner alight than they become invisible. The under surfaces of their wings, though varying greatly, yet form in every case a perfect representation of a leaf in some stage or other of decay, the butterfly at the same time disposing of the rest of its body so as to bear out the deception. How this is effected is best told by Mr Wallace, who was the first to observe it, in his valuable work on the Malay Archipelago.
“The habit of the species is always to rest on a twig and among dead or dried leaves, and in this position, with the wings closely fιressed together, their outline is exactly that of a moderately sized eaf slightly curved or shrivelled. The tail of the hind wings forms a perfect stalk and touches the stick, while the insect is supported by the middle pair of legs, which are not noticed among the twigs anti fibres that surround it. The head and antennae are drawn back between the wings so as to be quite concealed, and there is a little notch hollowed out at the very base of the wings, which allows the head to be retracted sufficiently.”
Moths, when at rest, have the hind wings folded close to the body, while the fore wings cover all, and it is the latter that usually show an assimilation in colour to surrounding nature. Many butterflies and moths, there seems good reason to believe, are coloured in imitation of other and often widely different species possessing some special means of protection, as sting or nauseous juices, the mimetic forms, it is supposed, sharing with their models in immunity from the attacks of insectivorous animals. The phenomena of mimickry were first observed by Bates among the Heliconidoe, a family of South American butterflies, remarkable for their great numbers, the gaudiness of their colouring in both sexes and on both surfaces of their wings, and for their comparative slowness of flight. It was found that, owing to the nauseous nature of their juices, those brilliant butterflies were left unmolested by insect-eaters. It was also observed that several species of a genus closely allied to our Cabbage Butterflies, totally different both in the colour and form of the wings from the Heliconidoe, so closely resembled particular species of the latter as not to be distinguishable from them on the wing. Exactly similar phenomena have been observed in the tropical regions of Asia and Africa, where the similarly protected Danaidoe and Acroeidoe find imitators among the otherwise unprotected Papilios and Diademas. There are two families of clay-flying moths, Sesiidoe and Aegeriidoe, with clear transparent wings, the scales being confined mainly to the margins and nervures, which in their wings and in the form and colour of their bodies might be readily mistaken for bees or wasps, a similarity recognized in such specific names as l)ombiciformis, apiformis, vespiformis, <kc., applied to different species of these moths. Other species of the same “clear wing” group have opaque wings closely resembling those of certain species of Coleoptera found in the same neighbourhood, and these have their wings when at rest closed over their bodies like the elytra of beetles.
Butterflies and moths undergo complete metamorphosis, that is, after emerging from the egg, and before attaining the full development of the imago, they pass through the larva and pupa stages—the latter being one of total inactivity in so far as the outward manifestations of life are concerned. The eggs vary greatly in shape, and are deposited in a great variety of situations—on the under sides of leaves, on the outside of the cocoon, as in the Vapourer Moth (Orgyia antiqua), the female of which is wingless, glued together in rings round the smaller branches of fruit trees, as in Clisiocampa neustria, or in the interior of hives, the larvae afterwards feeding on the wax, as in the Honey-comb Moth (Galleria cerelld), They thus show a remarkable instinct in depositing their eggs in situations where the larvae may afterwards obtain their appropriate food, although they themselves can have no knowledge of that food. The caterpillar emerges from the egg usually in a week or ten days. Unlike the perfect insect it is provided with a masticatory mouth. It has three pairs of legs on the anterior segments of its body, corresponding to the six legs of the future imago, besides which it is provided with a variable number of conical feet or prolegs placed posteriorly, and which are merely processes of the external covering of the caterpillar. Goossens, a Continental naturalist, has recently observed that the number of prolegs in some species differs at different ages, and gives a case in which a caterpillar with originally six prolegs acquired two additional pairs after the third moult. The body cavity is almost entirely occupied with the digestive system, and with that concerned in the production of the silky material used in forming the cocoon. Silk is secreted as a viscous fluid in tubes, which after many convolutions widen into a large reservoir filled with the yellow liquid, narrowing again into a tube extending to the mouth, where it communicates with the outside by means of a conical and jointed papilla known as the spinneret. Through this organ the viscous fluid is forced in two exceedingly delicate streams, which coalesce, and on exposure to the atmosphere harden into a single continuous thread. The silky material is not completely formed till the caterpillar reaches maturity. Caterpillars are either smooth skinned or more or less covered with hairs; in the former case they are a favourite food of insectivorous animals, while in the latter they are almost universally rejected,—recent investigations on this subject going to prove that the hairs on certain species of caterpillars have a power of stinging, somewhat analogous to that possessed by the hairs on the surface of a nettle.
No sooner does the caterpillar emerge from the egg than it begins to eat voraciously, and in a few days has grown so large that a change of skin becomes necessary. The old skin is cast off, and with it the entire internal lining of the alimentary canal, and in the majority of butterflies and moths five such changes take place before the caterpillar has attained its full growth, while the Tiger Moth (Arctia caja) is said to cast its skin at least ten times. Those moultings do not usually affect the appearance of the caterpillar, except in enlarging it; but in the case of Samia cecropia, a species of Bombycidoe, the larvae are said to pass from black to various shades of green and azureblue in the course of their moultings. The larvae of the family Psychidoe — the larger members of which are found in America and Australia—have the curious habit of constructing cases which they carry about with them, and within which they afterwards undergo transformation. Each larva has but a single case, and when this gets too narrow it splits longitudinally and is enlarged by interpos ing a new portion between. Moths and butterflies remain in the larva) condition for periods varying from three years, as in the Goat Moth (Cossus ligniperda), to a few weeks, as in tbe Cabbage Butterfly (Pieris brassicoe), which usually has two broods in the season, while many species whose larvae leave the egg in autumn, as the Blue Butterfly (Polyommatus alexis), remain torpid throughout winter at this stage, and waken up to resume feeding in spring. During this period they increase enormously in weight; thus the larva of the Privet Hawk Moth (Sphinx ligustri) which casts its sixth and last skin on the twenty-second day after emerging from the egg, attains its greatest size ten days after, having in the meantime increased to 11,312 timesits original weight; while the Goat Moth (Cossus ligniperda), which remains in the larval condition for three years, has grown in that period 72,000 times heavier. Having attained its full growth the instincts of the caterpillar undergo a change; it ceases to eat and begins to weave a couch or cocoon by which it is more or less enclosed. It then throws off its skin and appears as a pupa or chrysalis incapable of eating or of locomotion, the only apparent sign of life which it manifests being a convulsive twitching when irritated. Examined more closely, however, life is seen to be exerted in very great intensity in this stage of apparent quiescence. The immense digestive system of the caterpillar dwindles greatly, the rudiments of wings begin to show themselves, forming slight prominences on each side of the chrysalis shell, while the organs of the masticatory mouth are being transformed into those of the suctorial. In assuming the pupa condition caterpillars dispose of themselves in a great variety of ways. Many, like the common Cabbage Butterfly, ascend walls and palings, to which they attach themselves by a silken belt, others, as silkworms, spin around them a solid cocoon of pure silk; while the majority of Sphinx Moths form burrows in the ground, which they line with silk and afterwards varnish to keep out the moisture,—one of these (Sphinx ligustri) remaining thus buried from August till June. Those larvae which feed on the wood of trees, as Cossus ligniperda, generally form tough cocoons of chips of wood and of silk within the tunnels which they have bored in the tree, and their pupae have the power of forcing themselves along those passages till they reach the bark, where they remain until about to emerge from the egg, when they pierce it also. The cocoon of the Puss Moth (Cerura υinula), composed of the same materials as in the preceding instance, is usually placed in a crevice of the bark of a tree, where by exposure to the atmosphere it becomes hard as horn, the moth only making its escape after discharging a liquid by which one end of the cocoon is softened. Hairy caterpillars are usually deficient in silk, and in forming their cocoons mix what they have of this with the hairs of their body. A beautiful net-like cocoon is woven by a South American moth belonging to the Bombycidoe, which it suspends from the top of an outstanding leaf. “When the caterpillar,” says Bates, “begins its work it lets itself down from the tip of the leaf which it has chosen by spinning a thread of silk, the thickness of which slowly increases as it descends Having given the proper length to the cord (about 6 inches) it proceeds to weave its elegant bag, placing itself in the centre and spinning rings of silk at regular intervals, connecting them at the same time by means of cross threads, so that the whole when finished forms a loose web with quadrangular meshes of nearly equal size throughout.” The duration of the pupa stage varies from a few weeks to several months; it varies also in the same species according to the season at which it becomes encased; thus the pupa of Vanessa urticoe at the beginning of summer usually develops in fourteen days, and at midsummer in eight or nine days, while if it becomes encased in autumn it remains a pupa during the winter. By applying heat the process can be accelerated, and it can be equally retarded by refrigeration. When mature the pupa case cracks towards the anterior end, and the butterfly or moth crawls forth with wings which, though at first small and crumpled up, in a few hours attain their full size. The male insect goes in search of the female, and when the latter has deposited her eggs the main object in the life of the imago is attained and both sexes die. Among the Bombycidoe this occurs in two or three days, owing to the atrophied condition of the organs of the mouth. W ith butterflies courtship is generally a more prolonged affair, several males pursuing the same female, and breaking each others wings in the conflicts that thus frequently ensue. Butterflies appear in many cases to be gregarious, flying in great flocks. Bates states that at one place in South America he noticed eighty different species flying about in enormous numbers in the sunshine, and these, with few exceptions, were males, the females remaining within the forest shades. Darwin also describes a “butterfly shower,” which he observed ten miles off the South American coast, extending as far as the eye could reach; “even by the aid of the telescope,” he adds,“it was not possible to see a space free from butterflies. That they are occasionally migratory as well as gregarious is borne out by the observations of Sir J. Emerson Tennent, who witnessed in Ceylon a mighty host of butterflies of a 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.”
The food of Lepidopterous insects consists chiefly of the sweet liquids drawn from the nectaries of flowers, which they reach by means of their long proboscis or tongue. Many of the Sphingidoe are said to do this without settling on the flowers, and one of these, the Humming Bird Hawk Moth of South America (Macroglossa titan), in its mode of flight and of poising itself before a flower while extracting the juice, bears such close resemblance to certain of the smaller humming birds inhabiting the same district, that Bates often shot it for one of the latter, and it was only after considerable experience that he learnt to distinguish the bird from the moth when on the wing. Although their food is thus usually the sweetest liquids drawn from loveliest vessels, still some of the most brilliant species seem to prefer more vulgar fare. Thus the showy Purple Emperor (Apatura iris) prefers above all things to suck the juices of putrid animal substances, and the surest way to secure specimens of this butterfly is by setting such baits near its haunts. Mr Wallace states that in Malacca he caught a large and brilliant butterfly which had settled on the dung of some carnivorous animal, where he had also observed it on the previous day, and he adds that it is a habit of many of the finest butterflies to suck up the liquid from muddy spots on the roadside.
Butterflies and moths are widely distributed all over the globe, occurring, however, in greatest variety and abundance in tropical lands. They are...
