The Moths of the British Isles Second Series/Chapter 11
ZYGÆNIDÆ.
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The moths belonging to this family are popularly known in Britain as Burnets and Foresters. Of the former seven kinds occur in the British Isles, and of the latter there are only three species.
All the species live in colonies, so that when a specimen is seen or captured others may be expected to occur on, or somewhere around, the same spot. The caterpillars bear a close resemblance to each other, and are not always easily distinguished.
Over thirty species of Zygæna are found in Europe, and about thirty-six more have been described from other parts of the Palæarctic Region. There are at least twenty-five Palæarctic species referred to the genus Ino, and about ten of these are European.
By most authors filipendulæ is regarded as the type of the genus Zygæna, Fabricius; but others refer this species, and its allies, to the genus Anthrocera, Scopoli, using the Fabrician genus for phegea, Linnæus. The latter species and its allies are perhaps more frequently referred to Syntomis, Ochsenheimer, the typical genus of the family Syntomidæ, the systematic position of which is near the Arctiidæ. It may be added that S. phegea, and also Naclia ancilla, have been reported as British. There does not seem, however, to be any reason to suppose that the occurrence of either species in Britain could be other than accidental.
The Transparent Burnet (Zygæna purpuralis).
Two Welsh specimens are depicted on Plate 146, Figs. 1 and 2; these are of the typical form. A rare aberration has the spots and the hind wings more or less suffused with blackish (ab. obscura, Tutt), but a still rarer variety has the crimson of spots and hind wings replaced by yellow (ab. lutescens, Tutt).
Newman in 1861 referred an Irish specimen to achilleæ, but a little later, after seeing other examples, in the same year he changed the name to nubiginea. Birchall (Ent. Mo. Mag., iii. pt. i.) figured four forms of the species from Ireland; his minos (Figs. 5a and 5b) seems to represent two modifications of ab. interrupta, Staudinger, in which form the red blotches are widely separated or interrupted by the ground colour; and his nubigena is made up of more or less typical purpuralis (Fig. 6a), and a variety (Fig. 6b), with red marks between the lower and central blotches.
The caterpillar (Plate 145, Fig. 1) is dark green inclining to olive above and paler below; the spots are black (outer row) and yellow (inner row); the line along the back is obscure whitish; hairs, whitish. It feeds on thyme and burnet saxifrage (Pimpinella). Trifolium and Lotus have also been given among other food plants. In late summer, and after hibernation, in the spring. The moth flies in June, and is locally common in Ireland (Clare and Galway), Wales (Abersoch), and Scotland (Oban, Loch Etive). It has been reported from Tintagel, Cornwall, and possibly, as suggested by Tutt, these Cornish specimens may turn out to be Z. achilleæ, the latest addition to our small band of Burnets. Perhaps the Scottish specimens recorded as purpuralis, or at least some of them, may prove to be achilleæ.
This species was figured by Brünnich, in 1763, as purpuralis, and authorities are now agreed that this name must be adopted in place of pilosellæ, Esper (1781), or minos, Fuessly (1782).
Scotch or Mountain Burnet (Zygæna exulans).
This semi-transparent and rather greyish moth has five reddish spots on the fore wings. (Plate 146, Fig. 3.) So far as concerns the British Isles it is only known to occur in Aberdeenshire, where it was discovered on the mountains at Braemar in July, 1871, and where it may be still found by those who are acquainted with the situation of its lofty haunts. The late Dr. Buchanan White named the Scottish form subochracea, but others consider that it is not readily separable from vanadis, Dalman, which in turn is said by Tutt to be pretty much the same form of the species as that described as the type exulans, Hochenwarth.
The caterpillar is dark green above, and paler below; two velvety black stripes on the back, each stripe interrupted by yellow spots; warts with black hairs; head, black. It feeds on Silene acaulis, cyphel (Arenaria cherleria = Cherleria sedoides), clover, trefoils, Azalea procumbens, etc.; has been known to eat dock and knot-grass: August to June. The cocoon has been found on a stem of crowberry (Empetrum), and on heath and grass stems. The moth is out in July, and, like the rest of its kindred, delights in the sunshine.
Zygæna achilleæ.
A specimen of this species, quite recently introduced as British, has been kindly lent by Mr. B. Adkin. It was taken, with others, in the vicinity of Oban, Argyllshire. Mr. Sheldon informs me that he believes that a worn Zygænid he captured in 1898, in the Glencoe district, was this species.
On Plate 1, with the Scottish example (Fig. 2) referred to, is also shown a specimen from the continent (Fig. 3), and it will be noted that the former is very like the latter. In some respects this species is not unlike some confluent-spot forms of filipendulæ, but it is a more slender-looking insect, and the body is more hairy. Further, the upper basal spot of the fore wings is lengthened almost to the upper spot of the middle pair, and the fifth and sixth spots together form an almost oval mark. Both specimens depicted seem to be referable to var. viciæ, Hübner. In the typical forms the spots are larger. A yellow form ab. flava, Oberthür, is known on the continent.
The caterpillar, after Hofmann, is figured on Plate 1, Fig. 5. It is said to feed on Astragalus and Coronilla.
New Forest Burnet (Zygæna meliloti).
Two examples of this, normally, five-spotted little species are shown on Plate 146, Figs. 4 ♂, 5 ♀; a variety, referable to ab. confusa, Staudinger (spots run together forming streaks somewhat as in purpuralis), is depicted in Plate 148, Fig. 1. Occasionally a sixth spot is in evidence (ab. sexpunctata, Tutt). A form in which the body has a red belt is known abroad as ab. stentzii, Freyer, and examples having traces of this belt have been recorded from the New Forest, which, it may be added, is the only locality in Britain producing this species.
The caterpillar is of a dull pale greenish colour, with numerous black speckles; three whitish lines on the back, the central one greenish tinged and broader than the others, which are interrupted on each ring by a yellow spot; between the lines is a series of black dots, one on the outer edge of each ring; hairs, from greenish warts, white and short; head, black, dotted with white. It feeds on bird's-foot trefoil (Lotus corniculatus), and other trefoils and clovers: August to May. Sometimes the caterpillars do not complete growth until they have passed two winters in hibernation. The cocoon, which is yellow or yellowish white, has been found on a grass stem, but it is generally placed so low down among herbage that it seems to be rarely detected.
The moth is out in June and early July.
As previously stated the only part of Britain that the species inhabits is the New Forest, Hampshire. Here it was first met with in Stubby Copse, about 1869, but was apparently not distinguished from Z. trifolii until 1872. It is now less frequent in its old haunt than formerly, although it still occurs there; in other spots around, I believe, it is not uncommon in some years.
Some authorities refer this species to viciæ, Schranck.
Five-spot Burnet (Zygæna trifolii).
Four specimens of this species are portrayed on Plate 146. In the typical form (Figs. 7 ♂, 8 ♀) the central pair of crimson spots are united and often form a large blotch; ab. orobi, Hübner (Figs. 6 ♂, 9 ♀), has the spots placed well apart. Other more or less frequent aberrations are depicted by Mr. Horace Knight on Plate 148 where Fig. 2 represents ab. glycirrhizæ, Hübner (spots 3, 4, and 5 united); Fig. 3, ab. basalis, Selys (spots 3 and 4 united with the basal pair); and Fig. 4, ab. minoides, Selys (all the spots united, forming an irregular patch). An extreme development of the last-mentioned form has been named ab. extrema, Tutt (see Entom. xxix., p. 341, Fig. 2). Specimens with a sixth spot as in Z. filipendulæ have been occasionally recorded, and an example with the lower spot of the central pair absent has been taken in West Sussex by Mr. W. M. Christy, who has also obtained a number of specimens of a yellow form (ab. lutescens, Cockerell) in the same locality. The yellow form is shown on Plate 148, Fig. 5. Some of the yellow aberrations also exhibit variation in the spots pretty much as in the ordinary form. In some localities, especially marshy ones, the spots on the fore wings and the hind wings are occasionally dull orange; and I have noted specimens in the Weybridge district, Surrey, with the spots on the fore wings of a pinky ochreous colour, whilst the hind wings were of the usual crimson. Such "aberrations" as those last mentioned probably result from weather exposure. In 1899, Mr. G. B. Corbin recorded the capture, near Ringwood, Hants, of a specimen which had the spots on the fore wings and the red of the hind wings darkened over with dull smoky black, so that the insect when seen at a distance seemed to be wholly black. Dr. Hodgson has recently obtained several of these melanic specimens in Sussex. A form with the spots and hind wings suffused with brownish has been named ab. obscura, Oberthür.
With regard to six-spot examples referred to this species, I am inclined to suppose that they may be the offspring of a chance pairing of trifolii and filipendulæ. That such crossing does occur in nature I have evidence, as on one occasion I found four mixed pairs, the male being trifolii in each case, and the female typical filipendulæ. This was in the Weybridge district, where I had come across a colony of the latter species and was closely examining the specimens for aberrations.
The caterpillar (Plate 145, Fig. 3) is green inclining to yellowish and to bluish, with black marks on the back; a series of black streaks low down along the sides. It feeds on Lotus corniculatus, and on other trefoils and clover: July to May. Sometimes taking two years to complete its changes.
In damp meadows the moth is out in May and June, but in marshes it does not appear, as a rule, until July, and may be found in early August. The marsh specimens, which are sometimes rather large in size, have been referred to palustris, Oberthür, and are treated by Tutt (Nat. Hist. Brit. Lep., vol. i.) as a sub-species.
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| 10, 11. Cistus Forester. |
In the British Isles, the species is apparently confined to England and North Wales. In the former country it is locally common in most of the southern counties; still more local in the eastern counties, and northwards to Lancashire and Yorkshire. There are records from Armagh and Fermanagh, but Kane appears to doubt the occurrence of the species in Ireland. There is no doubt that the next species has frequently been mistaken for the present one, therefore the actual range of trifolii in the British Isles has probably not been fully ascertained.
Narrow-bordered Five-spot Burnet (Zygæna loniceræ).
As will be seen from the two specimens represented by Figs. 1 ♂ and 2 ♀ on Plate 147, this species bears considerable resemblance to ab. orobi of Z. trifolii. The chief differences are in the rather longer fore wings and the more pointed tips of the hind pair; the borders of the hind wings are often narrower. In a broad way, it may be stated that the general tone of colour in the male of loniceræ is bluer than that of trifolii. The union of any two or more spots is rarely seen in this species in Britain, but specimens with all the spots joined together have certainly been noted. A yellow form, ab. citrina, Speyer (= flava, Oberthür), is known on the continent, and Barrett states that it has occurred in England. In ab. lutescens, Hewett, the hind wings are orange. Ab. eboraceæ, Prest, is semi-transparent, steel blue; the spots and the hind wings are pink, the border of the hind wings brown, and the fringes of all the wings are whitish.
The caterpillar (Plate 145, Fig. 2) is very similar to that of the last species, but the black marks on the sides are heavier, and the hairs of the body are longer. It feeds on trefoils and clover, and sometimes passes two winters before becoming full grown. The cocoon, which is attached to stems of grass, etc., is generally placed well up above the ground, so that it is readily seen.
The moth, which is out in late June and in July, occurs in woods and plantations; also said to be found in meadows, and on rough waste ground, as well as in marshes and salterns. The distribution is much as in the last species, but it is plentiful in East Yorkshire, and the range extends to Cumberland and Northumberland.
Six-spot Burnet (Zygæna filipendulæ).
This species (Plate 147, Figs. 3-5) is the most generally common of our Burnets. Perhaps the most frequent form of variation in the spots of the fore wings is that in which the outer pair run together, and so form a blotch; but union of the middle pair is not an uncommon occurrence. In ab. cytisi, Hübner, the three pairs of spots are each united, so that the fore wings have three separate blotches, and when these are of a dull scarlet instead of the usual crimson, ab. ramburi, Lederer, is represented. Occasionally, all the spots are united, as in ab. cytisi, and the blotches thus formed are connected by reddish streaks in various modifications leading up to ab. conjuncta, Tutt, which has all the spots merged into a large blotch, extending over the disc of the fore wings. From the normal crimson, the spots and the hind wings vary now and then to orange (aurantia, Tutt), or to yellow (ab. flava, Robson = cerinus, Robson and Gardner); intermediate shades between these two extremes, and the typical coloration, are rather more frequent. I am indebted to Mr. R. Adkin for the loan of the example of the yellow form shown on Plate 148, Fig. 6. Pink, and orange, forms have been noted from various parts of England, but they seem to occur, or have been found, more especially in Cambridge and the north-east corner of Essex. Fig. 7, Plate 148, represents an example of ab. chrysanthemi, Hübner, and is copied from Oberthür's Etudes d'Entom., xx., Plate 8, Fig. 134. A few specimens referable to this form, probably not exceeding half a dozen altogether, have been recorded as taken in England. In typical filipendulæ the dark blue border of the hind wings is narrow, but in ab. hippocrepidis, Stephens (tutti, Rebel), the borders are rather broad. Another character of this form is that the nervule upon which the sixth spot is placed is here of the ground colour, and therefore divides the spot. (Plate 147, Fig. 3.) At Northwood, Middlesex, I have found this form in May and June, and also in the Weybridge district, Surrey, in late July; and, it may be added, there was a flourishing colony of Z. trifolii hard by in each locality. For this reason, plus the fact that trifolii ♂ is known to pair with filipendulæ ♀, I hold the opinion that hippocrepidis is a hybrid. It may be noted here that hybrids have been raised from the crossing of filipendulæ and loniceræ; the sexes of loniceræ and trifolii pair somewhat readily, and the hybrid offspring of such pairings are fertile.
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| 6, 7. Six-spot Burnet, vars. |
It seems, then, that trifolii, loniceræ, and filipendulæ have not, so far, lost the power of fertile cross-pairing. Wherever colonies of two of the kind exist within visiting distance of each other, there, it appears, we may reasonably expect to find hybrids.
From a number of cocoons collected in a Yorkshire locality for loniceræ, I reared, in 1907, a good many examples of that species, and also about a dozen six-spot specimens, which agree in colour with filipendulæ, but they have the vein-interrupted sixth spot and broad border to hind wings, as in hippocrepidis.
The caterpillar (Plate 145, Fig. 4) is greenish, with black markings and some yellow spots, the latter chiefly on the hind edges of the rings. It feeds in the autumn and after hibernation, on trefoils, clover, bird's-foot (Ornithopus), and kidney-vetch (Anthyllis), completing growth in the spring.
The moth flies on sunny days in July and August, on chalk downs, etc., inland, and on cliffs and sand hills on the coast, also in marshes; but, as previously stated, it also occurs locally in meadows in May and June.
Scarce Forester (Ino (Rhagades) globulariæ).
Of the three species occurring in Britain this is slightly the larger, at least in the male. The fore wings are green, sometimes with a slightly golden sheen; fringes, greyish. The male is best distinguished from statices by its more slender body, and by the pectinated and rather pointed antennæ. The female is a good deal smaller than the male; the antennæ are simple, and somewhat thread-like, compared with those of the females of statices and geryon. (Plate 147, Figs. 6 ♂, 7 ♀.)
The caterpillar is green, with the raised spots inclining to bluish; two yellowish-white lines along the back, and a dark green stripe along the sides; head and plate on first ring of the body, black. It lives on knapweeds (Centaurea nigra and C. scabiosa), feeding on the leaves much in the same manner as the caterpillar of the next two species.
The moth is out in June and July; it is partial to blossoms of salad burnet (Poterium sanguisorba), and only flies in the sunshine. The late Mr. J. Jenner Weir, who found the species commonly on the downs near Lewes, Sussex, was the first entomologist to record it as British. The best known localities in Sussex are Hollingbury Vale and Cliffe Hill, but it also occurs at the Devil's Dyke near Brighton. In Kent it is found on the downs behind Folkestone and Shorncliffe Camp.
The Forester (Ino (Adscita) statices).
In its most frequent form in Britain, this species is bronzy green (ab. viridis, Tutt); the typical bluish green type is much less frequent. The female is smaller than the male, but the difference in size is hardly ever so marked as in the sexes of globulariæ. The antennæ of the male are pectinated, but the tips are thickened. (Plate 147, Figs. 8 ♂, 9 ♀.)
The caterpillar (Plate 145, Fig. 5) is whitish, inclining to green, yellow, or pinkish, on the back, and the sides are pinkish brown; the hairy warts are brown or pinkish brown, and the small head is glossy black. It feeds on sorrel (Rumex acetosa), and it attains full growth, after hibernation, about the end of April. On leaving the egg-shell in the summer, the young caterpillar bores into a leaf, and eats the tissue between the upper and lower skins; later on it attacks the foliage from the underside, but leaves the upper skin intact; or the process may be reversed, and the under skin left.
The moth is on the wing in June, sometimes late May. It occurs, locally, in meadows, frequently damp ones, where there is plenty of ragged-robin (Lychnis flos-cuculi), the blossoms of which plant it seems to prefer to all others.
Widely distributed over England, but in Wales only recorded from Capel Curig and Barmouth, in the north of that country (1900). In Scotland its range extends to Moray; and in Ireland it is found in counties Wicklow, Cork, Clare, Westmeath, Monaghan, Sligo, and Galway.
Cistus Forester (Ino (Adscita) geryon).
This species is much smaller than the last; the fore wings, the outer margins of which are somewhat rounded, are bronze green, but, in the male, rather dull in tint, sometimes tinged with golden towards the base. The antennae are more stumpy than those of statices, but in other respects they are similar in appearance. The female is not much smaller than the male. (Plate 147, Figs. 10 ♂, 11 ♀.)
The caterpillar is yellowish white, with bristle-bearing warts of pretty much the same colour; three lines on the back, the central one whitish, edged on each side with purplish, the others waved and of a claret colour; a reddish-brown stripe low down along the sides; head and plate on first ring of the body black, the latter edged in front with yellowish. It feeds on rock rose (Helianthemum chamæcistus). At first it attacks the leaf from the upper side, and partly burrows therein; when older it clears away patches from the under surface, leaving the upper skin of the leaf more or less transparent; as it approaches full growth it likes to take its meals in the sunshine, and then eats the top skin as well as other parts of the leaf, and also tender shoots: July to May. The moth is out in June and July, as a rule, but is sometimes observed in May. Its haunts are on warm slopes of chalk downs and limestone hills, where it flies in the sunshine.
This species was first noted as British in March, 1860, when specimens from Worcestershire were recorded as Procris tenuicornis. It seems, however, to have been considered doubtfully distinct from statices until 1863, when the caterpillar was found, and the occurrence of the species in several other English counties recorded. At the present time I. geryon is known to inhabit Sussex (Brighton and Lewes districts), Kent (Canterbury and Shorncliffe), Bucks (Aylesbury and Tring), Oxfordshire (Chinor), Gloucestershire (Cotswolds), Worcestershire (Malvern Hills), Derbyshire and North Staffordshire (Bakewell and Dovedale), Yorkshire (Richmond, Barnsley, Sheffield, etc.), and Durham (banks on the coast). In Wales, it is sometimes common on Great Orme's Head, Carnarvonshire.