The Large Blue (Nomiades Arion)
The butterfly on Plate 117, Figs. 1-6, is the largest “Blue” found in this country. All the wings on the upper side are deep blue, and their outer margins are bordered with blackish; the discal spot, and a row of spots beyond, are black; the hind wings have a row of black dots on the outer margin, and sometimes, and especially in the female, there is a series of black dots just beyond the central area; the fringes are white. The under side is greyish tinged with blue towards the base of each wing, but covering nearly the whole of the basal third of the hind pair; the spots are black ringed or edged with white; on the fore wings there are two in the discal cell and a row of six beyond; on the hind wings there are four or five before the discal spot, and a series of seven beyond; all the wings have a double marginal series, and some black dots at the ends of the nervules. Sometimes the wings have a purplish tinge, and this is more usually so in Gloucestershire specimens. The chief variation is in the number and the size of the spots; these are occasionally only faintly in evidence, but more rarely perhaps those beyond the discal spot on the fore wings are of large size and bar or wedge-like in shape; the smaller cell-spot is often absent. A dwarf form is stated to occur at times in all localities.
The complete life-history of this species has yet to be ascertained; no one seems to be acquainted with the caterpillar after hibernation. Pretty much all that is known of the early stages has been worked out by Mr. Frohawk, who has published some very interesting accounts of his observations in the Entomologist for 1899 and 1903, and from these the following details have been obtained.
The egg (Plate 116) is bluish-white in colour, and is laid singly among the buds of wild thyme (Thymus serpyllum).
Caterpillars hatched on July 10 from eggs received the previous day; they were placed upon thyme blossoms and soon commenced to feed, one being observed to eat its way into the base of the calyx so that the forepart of the caterpillar was hidden. In its colouring and downy covering the caterpillar so closely resembles the flower-buds of the thyme that it is very difficult to detect. After the third moult (July 26) the colour is a uniform, dull, ochreous-pink; there are four rows of long curved hairs, each row composed of a single hair on each ring from the fourth to the ninth inclusive; the first three rings have each a set of three subdorsal hairs, those on the first ring curving forwards; the bases of the hairs resemble glass-like pedestals with fluted sides. The head is ochreous with dark brown markings in front. The caterpillar at this stage develops an aversion to thyme or any other plant offered to it, and seems to be anxious to hide itself in the ground.
The chrysalis, which is figured on Plate 116 (after Frohawk), is ochreous when first formed, but becomes darker gradually; the wing-cases, however, remain of the original colour, but their hind margins darken. From a chrysalis found on July 12 the butterfly emerged on July 16.
There is some evidence in favour of the supposition that this caterpillar is in some way dependent upon ants for nourishment after the third moult, if not before, but what the exact requirement may be is not known. Probably the circumstances connected with the discovery of the chrysalis in 1905 by Messrs. Frohawk & Rayward may afford a valuable clue to the direction in which their future investigation will have to be conducted. We may hope, therefore, that the mystery that has so long hung over the last stages of the caterpillar will be solved before very long.
Lewin (1795) and Donovan (1796) both refer to this as a rare English butterfly. The former states that it is on the wing in July, and is found on high chalky lands in different parts of the kingdom, having been taken on the cliffs in the neighbourhood of Dover, Marlborough Downs, the hills near Bath, and near Clifden in Bucks.
Stephens, in 1828, wrote of it as “an insect of great rarity.” He mentioned the localities given by the older authors, and added that it had been taken in the Mouse’s Pasture, near Bedford, in rocky situations in North Wales, and had been plentiful near Winchester.
Newman (1871) wrote, “Its ‘metropolis,’ if I may borrow an expression from the revered fathers of British entomology, is in South Devon; it has occurred in some abundance in Somersetshire, and on the Cotswold Hills in Gloucestershire; from Gloucestershire we ascend to a Midland county, Northamptonshire, in which county (at Barnwell Wold) a considerable number have been taken.” One specimen was reported from Charmouth in Dorsetshire, and the butterfly has also been recorded from Herefordshire, but these are matters of ancient history. At the present time the species is only to be found in limited numbers in the Cotswolds; it seems to have become much rarer than formerly in its South Devon locality, i.e. Bolthead, near Plymouth; one never hears of it now from Clovelly, in North Devon, where, according to Dale, it was once reported to be abundant. In 1891 Messrs. Waterhouse obtained a fine series of specimens in West Cornwall, and since that time the district has been annually visited by an increasing number of entomologists. Judging from the “big bags” that are made each year it would seem that the butterfly has a very strong and widely distributed settlement in those parts.
Abroad it is distributed throughout Europe, except the Polar and the south-western parts, and is also found in Armenia, Bithynia, and South Siberia.
Our next species belongs to the Nemeobiinæ, a sub-family of Lemoniidæ = Erycinidæ. Only one member of the family is known to occur in Europe; this is Nemeobius lucina.
As the fore legs of the male butterfly are aborted, and are therefore useless for walking, the species would seem to come near the Nymphalidæ, in which the fore legs of the butterflies, in both sexes, are reduced. In its early stages, however, the species seems to be most nearly related to the Lycænidæ.