Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/658

Rh 594 BUTTEKFLI E S ing a new portion between. Moths and butterflies remain in the larval condition for periods varying from three years, as in the Goat Moth (Cossus ligniperda), to a few weeks, as in the Cabbage Butterfly (Pieris brassicce), 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 times its original weight ; while the Groat 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 cater pillar undergo a change ; it ceases to eat and begins to weave a couch or cocoon by which it is more or less enclosed. upa. 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 after wards 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 vinula), 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 Bombycidce, which it suspends from the top of an outstand ing leaf. &quot; When the caterpillar,&quot; says Bates, &quot; 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.&quot; The duration of the pupa stage varies from a few weeks to several months ; ii varies also in the same species according to the season at which it becomes encased ; thus the pupa of Vanes&a urticce 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 Imago, 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 mam object in the life of the imago is attained and both sexes die. Among the Boinbyddae this occurs in two or three days, owing to the atrophied condition of the organs of the mouth. With 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 &quot; butterfly shower,&quot; which he observed ten miles off the South American coast, extending as far as the eye could reach ; &quot; even by the aid of the telescope,&quot; he adds,&quot; 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 obser vations of Sir J. Emerson Tennent, who witnessed in Ceylon a mighty host of butterflies of a white or pale yellow hue, &quot; apparently miles in breadth and of such prodigious extension as to occupy hours and even days uninterruptedly in their passage.&quot; The food of Lepidopterous insects consists chiefly of Food. the sweet liquids drawn from the nectaries of flowers, which they reach by means of their long proboscis or tongue. Many of the Sphingidce 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 distrut, 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 love liest 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 Distribn- globe, occurring, however, in greatest variety and abundance tion. in tropical lands. They are found as far north as Spitzbergen, on the Alps to a height of 9000 feet, and to double that height on the Andes. In Britain there are only GG, and in the whole of Europe 390 species of butterflies ; while within one hour s walk of Pard in Brazil, Bates found no fewer than 700 species. There are 1910 species of British moths, the majority of which are nocturnal and crepuscular ; while in tropical America day-flying moths seem to be most common, and may be seen in company with the sunshine- seeking butterflies. This paucity of nocturnal moths has been attributed to the great number of night-flying or crepuscular insectivorous bats and birds which haunt those regions. Many species both of moths and of butterflies have a very wide distribution ; the Painted Lady ( Vanessa