It occurs—only occasionally—in the Cotteswold district, and we suppose the same elsewhere. One meets with it here and there in the hedge-rows, and in Oakley Park, the seat of Earl Bathurst, we can point out a few specimens.
Galls of the Cynips Quercus petiolata.
(Natural size.)
Passing from the subject of the varieties of our British oak, it now remains to mention a most formidable enemy by which it has of late years been attacked, and so exclusively, that in plantations where may be found the American oaks, the Ilex oak, and Turkey oak trees, it has been the only one subjected to the operations of the new gall pest. It has long been known that our native oaks were subject to excrescences of different forms and sizes, such, for example, as oak-apples, oakleaf galls, oak spangles, &c., all of which were ascertained to be caused by several species of cynips; but lately we have to lament the introduction of a new species of the same insect, forming a new kind of gall, which, instead of attacking the backs of the leaves, as does the oakleaf gall, occupies the stem that belongs to the leaf; in fact, the attacked leaves seem to be converted into bunches of galls, as represented in the adjoining figure, which presents an illustration of the new pest. They are hard galls, more or less like the “nut-gall” from Aleppo, of which ink is made, and it will be seen that the little twig supports no less than five galls, in the interior of each of which may be found the maggot or larva of an insect; and, as this is affected at the expense of the buds and leaves, the mode of injury must be obvious, as the new twigs which would have been formed, had there been no galls, would in their turn have produced branches and leaves. Trees thus infested are crippled as though they had been subjected to constant pruning.
As much of the natural history of the cynips, by which these gall-nuts are formed, as is necessary for our purpose, may be gathered from a paper by Mr. Parfitt, who seems to have well studied the gall insect in Devon, its head-quarters. We quote it from the Journal of the Bath and West of England Agricultural Society for 1861:—
The eggs deposited by the females in the oak buds in September remain there in a state of apparent quiescence till the following spring; then, as soon as the sap begins to flow, the irritant injected into the wound at the same time the egg was deposited, or possibly the combined action of the egg and irritant, causes the sap to diverge; that portion of the bud which should have formed a young shoot is converted into a spherical ball; the outer scales of the bud fall away, and it is the woody secretion which entirely forms the gall. The cells in the gall are not elongated and regular, as in the young shoot, but confused and irregular; and in the centre of each gall lies a young grub of the cynips, forming a living nucleus, around which is deposited a thin, hard, woody envelope, much more compact in substance than the sponge-like tissue which fills up the interstice between it and the shining outer coat of the gall. This compactness of structure is a necessary and all-wise provision of nature for protecting the delicate insect which lies within from destruction; for if the gall were composed entirely of large spongy cells, the rapid flow of sap in the early spring would be more than the creature could consume, and it would consequently be drowned. I am aware that some naturalists incline to the opinion that the larvæ of the cynips feed on the gall. From this view, however, I venture to dissent; for not only is it inconsistent with the structure of the creature’s mouth, and the position in which the young larvæ are invariably found, with the head tucked under the apex of the abdomen, but if they fed on the substance or crude material of the gall, the undigested parts would certainly be[288] found in the interior of its cell: in other words, the excrement would be there, for there is no outlet, and the lacteals or absorbent vessels of the gall could not take it up. I therefore think that the creature feeds entirely on the sap of the tree—an elaborate food fit for it without the need of mastication. This explains how it happens that the galls of commerce, with the insects in them, are so much better and dearer than those from which the cynips has escaped; in a word, the tannic acid is more abundant.
It has been before observed, that there are two broods of the insect in a season; thus, those which do not emerge from the gall in September remain on till the following April or May. This is a wise provision of nature for continuing the species, should anything befall the autumn brood; and it is the more deserving of notice, because the gall-producing cynips has a deadly enemy which accompanies or follows it in its flight from bud to bud, and deposits an egg wherever it finds the egg of the cynips. Here, as soon as the cynips larva is hatched, the larva of the parasite is hatched also; forthwith the latter proceeds to eat a hole in the skin of the rightful occupant of the nidus, and the two larvæ go on growing together till the cynips is ready to assume the pupal state; then the parasite cuts the vital thread of the cynips, and uses its skin for a pupal envelope for itself; and thus, instead of the gall-fly emerging into day, a beautiful green insect makes its appearance on the stage of life. I had the pleasure of first discovering this parasite while engaged in studying the cynips; it belongs to the genus Callimone, and from the fact of having discovered it in Devonshire, I gave it the name of Callimone Devoniensis. It is one of the handsomest of our British insects; its costume a brilliant green, shot with gold; the abdominal segments green, gold, and purple; legs yellow; tarsi reddish; and it has four beautiful transparent and iridescent wings.
It has been stated that oak-galls are produced at the expense of acorns. From this view my experience leads me to dissent. In exceptional instances it may have been the case; but as a rule the cynips confines its attacks to young trees and young growths in hedges, within a range of ten or twelve feet from the ground, and the nearer the ground the more numerous the galls. Young trees which have not attained a greater height than that I have indicated suffer so much that many of them can scarcely make headway against their foe; and in several nurseries I have visited, where it might be expected that[289] greater care would be paid than in the case of ordinary plantations, the young stock of oaks has been rendered quite unsaleable by the pest. This year I have noticed the progress of the insect on two groups of young English and Turkey oaks growing side by side; and although there are hundreds of galls on the English oaks, there are none on the Turkey oaks. From this I am led to infer that the species of cynips now under notice is confined in its depredations to the English oak; and as it invariably selects trees of younger or restricted growth—probably because the temperature at a higher elevation than ten or twelve feet from the earth is unfavourable to it—it would seem that children might be advantageously employed in young plantations in collecting the galls by means of cutting-hooks, such as are used for thistles. The galls, when once collected, might either be crushed for tanning purposes, or consumed by fire, and if the process were repeated for two or three seasons, it is more than probable that the plantation would be altogether free from the pest.
These able remarks not only well describe the nature of the attack, but also point to a cure—a matter to which we would direct the most serious attention of the planter; for we may state that, in 1853, we saw some very small oak trees, in the neighbourhood of Dawlish, Devon, from which some hundreds of these galls might have been gathered. This was the first time we had noticed this pest, though it appears that it had been under Mr. Parfitt’s notice as long as a dozen years. Since then (1853) we have traced it in its progress as follows:—
Having observed the galls in Devon in 1853, we were yearly on the look-out in the Midland and Eastern counties for its appearance, and the following dates will show that its spread, though gradual, was sufficiently rapid:—
| The galls were gathered in Devon in | 1853 |
| The same kind in Somerset, in | 1854 |
| In Gloucester, on the west side of the river Severn, Forest of Dean, in | 1855 |
| In Gloucester, east side of the Severn, and as far as Oakley Park, Cirencester, in[290] | 1856 |
| In Worcestershire, in | 1857 |
| In North Wales, Beddgelert (pointed out to us by John Savory, Esq.), in | 1859 |
| In Sussex, very sparingly, in | 1860 |
| In Alice Holt Forest, and far from abundant, in | 1861 |
| About Hastings, very plentifully, in | 1862 |
We have this season observed a lot of the young galls; but last year, for the first time, we discovered that, in many cases, the maggot had been extracted by some small bird, one of the titmice (Parus cæruleus); and, if so, wherever young oaks may be growing, it should afford an additional reason for the protection of these useful birds. The magnitude of the evil, unless checked by some means, may be estimated from the fact that, in 1856, we could scarcely find half a dozen galls within a wide district, and now all around may be found trees, not more than 10 feet high, upon which are no less than from one to five hundred distinct galls.