Lepidoptera The Swallow-tail Butterfly – Papilio Machaon
Our first family (Papilionida) contains only one British species-the beautiful Swallow-tail (Papilio Machaon), distinguished at once from all other British butterflies by its superior size and the ‘tails’ projecting from the hind margin of the hind wings.
This beautiful insect is figured on Plate I, where its bold black markings on a yellow ground are so conspicuous as to render a written description superfluous. Attention may be called, however, to the yellow scales that dot the dark bands and blotches, making them look as if they had been powdered; also to the blue clouds that relieve the black bands of the hind wings, and the round reddish orange spot at the anal angle of each of the same wings.
It appears that this butterfly was once widely distributed throughout England, having been recorded as common in various counties, and has also been taken in Scotland and Ireland; but it is now almost exclusively confined to the fens of Cambridgeshire, Huntingdonshire, and Norfolk. Occasionally we hear of the capture of single specimens quite outside these localities, sometimes even in most unlikely spots, where its food plant does not abound. But we know that Machaon is a general favourite with entomologists, and that it is sent in the pupal state, by post, to all parts of the kingdom; so that the occasional capture of the insect far beyond the borders of its haunts is probably the outcome of an escape from prison, or of the tender-heartedness of some lover of nature who could not bear to see such a beautiful creature deprived of its short but joyous, sunny flight.
You cannot hope to see this splendid butterfly on the wing unless you visit its haunts during its season-May to August; but the pupa may be purchased for a few pence each from most of the entomological dealers; and if you obtain a few of these and watch them closely, you may be fortunate enough to see the perfect insect emerge from its case, and witness the gradual expansion of its beautiful wings.
The larva (Plate VIII, fig. 1), too, is exceedingly beautiful. Its ground colour is a lovely green, and twelve velvety black rings mark the divisions between the segments. Between these are also black bars, all spotted with bright orange except the one on the second segment.
A remarkable feature of this larva is the possession of a forked, Y-shaped ‘horn,’ that is projected from the back, just behind the head, when the creature is alarmed. If it is gently pressed or irritated in any way, this horn is thrust out just as if it were an important weapon of defence. And perhaps it is, for it is the source of a powerful odour of fennel-one of the food plants of the caterpillar-that may possibly prove objectionable to some of its numerous enemies.
The food plants of Machaon are the milk parsley or hog’s fennel (Peucedanum palustre), cow-parsnip (Heracleum sphondylium), and the wild angelica (Angelica sylvestris); but in confinement it will also partake of rue and carrot leaves.
The caterpillar of this species may be found in the fens during the greater part of the summer. It turns to a chrysalis in the autumn, and remains in this state throughout the winter, attached to the stems of reeds in the vicinity of its food plants. The perfect insect is first seen in May, and is more or less abundant from this time to the month of August.