Читать книгу The Butterflies of the British Isles - Richard South - Страница 14

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The Swallow-tail butterfly is the only British member of the extensive and universally distributed sub-family Papilioninæ, which includes some of the largest as well as the most handsome kinds of butterfly. Our species has yellow wings ornamented with black, blue, and red, and is an exceedingly attractive insect. The black markings are chiefly a large patch at the base of the fore wings, this is powdered with yellow scales; a band, also powdered with yellow, runs along the outer or hind portion of all the wings. There are also three black spots on the front or costal margin, and the veins are black. The bands vary in width, and that on the hind wings is usually clouded more or less with blue. At the lower angle of the hind wings there is a somewhat round patch of red, and occasionally there are splashes of red on the yellow crescents beyond the band. The male and female are shown on Plate 2.

The eggs are laid on leaflets of the milk parsley (Peucedanum palustre), which in the fenny home of the butterfly is perhaps the chief food-plant of the caterpillar. This is one of the few eggs of British butterflies that I have not seen. Buckler says that it is globular in shape, of good size, greenish yellow in colour when first laid, quickly turning to green, and afterwards becoming purplish.

The caterpillar when full grown, as figured on Plate 1, is bright green with an orange-spotted black band on each ring of the body, and blackish tinged with bluish between the rings. The head is yellow striped with black. When it first leaves the egg-shell, which it eats, the caterpillar is black with a noticeable white patch about the middle of the body. After the third change of skin it assumes the green colour, and at the same time a remarkable V-shaped fleshy structure of a pinkish or orange colour is developed. This is the osmaterium, and is said to emit a strong smell, which has been compared to that of a decaying pine-apple. The organ, which is extended in the figure of the full-grown caterpillar, is not always in evidence, but when the caterpillar is annoyed the forked arrangement makes its appearance from a fold in the forepart of the ring nearest the head. Other food-plants besides milk parsley are angelica (Angelica sylvestris), fennel (Fœniculum vulgare), wild carrot (Daucus carota), etc. From eggs laid in May or June caterpillars hatch in from ten to twelve days, and these attain the chrysalis state in about six or seven weeks. If the season is a favourable one, that is fine and warm, some of the butterflies should appear in August, the others remaining in the chrysalids until May or June of the following year; a few may even pass a second winter in the chrysalis. Caterpillars from eggs laid by the August females may be found in September, nearly or quite full grown, and chrysalids from October onwards throughout the winter. They are most frequently seen on the stems of reeds, but they may also be found on stems or sprays of the food-plants, as well as on bits of stick, etc. It would, however, be practically useless to search for the late chrysalids as the reeds are usually cut down in October, when the fenmen keep a sharp look-out for them, and few are likely to escape detection in any place that would be accessible to the entomologist.

Larger Image

Pl. 2.

Swallow-tail Butterfly.

1 male; 2 female.

Pl. 3.

Black-veined White Butterfly.

Eggs, natural size and enlarged; caterpillar and chrysalis.

On Plate 1 three forms of the chrysalis are shown. The figures are drawn from specimens collected in Wicken Fen in October, 1905. Occasionally a much darker, nearly black, form is found.

This butterfly was known to Petiver and other early eighteenth-century entomologists as the Royal William. There is every reason to believe that at one time it was far more widely distributed in England than it now is. Stephens, writing in 1827, states that it was formerly abundant at Westerham, and gives several other localities, some very near to London.

During the last twenty-five years or so, the butterfly has been seen on the wing, from time to time, in various parts of the Southern and Midland counties. Caterpillars have also been found at large in Kent. Possibly attempts may have been made to establish the species in certain parts of England, and the presence of odd specimens in strange places may thus be accounted for. Or such butterflies may have escaped from some one who had reared them.

On the Continent the butterfly is common in woods as well as in meadows, and even on mountains up to an elevation of 5000 feet. It occurs also, but less commonly, at much higher altitudes. It therefore seems strange that in England it should be confined to the low-lying fens of Norfolk and Cambridgeshire. Such is the case, however, and a journey to one or other of its localities will have to be made by those who wish to see this beautiful creature in its English home.

It may be added that the geographical range of the butterfly extends eastwards through Asia as far as Japan. A form, known as the Alaskan Swallow-tail, is found in Alaska.

The following ten species belong to the Pierinæ, another sub-family of Papilionidæ.