Quite early in the eighteenth century Petiver met with the butterfly shown on Plate [80] at Enfield, so he figured it as the "Enfield Eye" in that curious old book entitled "Papiliorium Britanniæ Icones." Later on, Wilkes named the butterfly the "Wood Argus," thus indicating its favourite haunts, as well as a prominent character in its ornamentation. Harris changed the name to the "Speckled Wood Butterfly," which seems even more suitable.
The general colour is blackish-brown, and the spots are yellowish. The fore wings have one white-pupilled black eye spot towards their tips, and the hind wings have three such eye spots on the outer area. The male has a long oblique patch of blackish scales on the middle of the fore wings, which is, perhaps, more easily detected if the insect is held up to the light. The female is usually slightly larger than the male, the wings rather rounder, and the yellowish spots, are, as a rule, distinctly larger. The typical or southern form of this butterfly has the spots of a tawny colour, but it does not occur in Britain. Our form, in all its modifications, belongs to egerides, Staudinger. Occasionally, in the south of England, specimens are found in which the spots are tinged with fulvous; others have almost white spots. The spots are sometimes much reduced in size in the male, or greatly enlarged in the female.
The egg is pale greenish, finely reticulated; as the caterpillar matures within, the shell becomes less glossy than at first, and the upper part is blackish.
The caterpillar has a green head, which is larger than the first ring of the body (1st thoracic), covered with short fine whitish hairs, with which are mixed a few dark hairs. The body is rather brighter green, with darker lines, edged with yellowish, along the back and sides; the skin is transversely wrinkled, the rings being subdivided, and the whole of the body is clothed with fine whitish hair and a few dark hairs arising from warts; the anal points are whitish and also hairy. It feeds on various grasses, among which are Triticum repens and Dactylis glomerata.
Larger Image
Pl. 80.
Speckled Wood.
Spring Brood: 1, 2 male; 3, 5 female. Summer brood: 4, 6 male; 7 female.