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devour, and thus proceed, from leaf to leaf, down the branch, till they have grown to their full size. They then average five eighths of an inch in length, are somewhat slender and tapering behind, and thickest before the middle. They have twentytwo legs. The head and the tip of the tail are black; the body, above, is light green, paler before and behind, with two transverse rows of minute black points across each ring; and the lower side of the body is yellowish. After their last moulting they become almost entirely yellow, and then leave the vine, burrow in the ground, and form for themselves small oval cells of earth, which they line with a slight silken film. In about a fortnight after going into the ground, having in the mean time passed through the chrysalis state, they come out of their earthen cells, take wing, pair, and lay their eggs for a second brood. The young of the second brood are not transformed to flies until the following spring, but remain at rest in their cocoons in the ground through the winter. For some years previous to the publication of my “ Discourse," I observed that these insects annually increased in number, and, in the year 1832, they had become so numerous and destructive that many vines were entirely stripped of their leaves by them. Whether the remedies then proposed by me, or any other means, have tended to diminish their numbers, or to keep them in check, I have not been able to ascertain, and have had no further opportunity for making observations on the insects themselves. At that time, air-slacked lime, which was found to be fatal to these false caterpillars of the vine, was advised to be dusted upon them, and strewed also upon the ground under the vines, to insure the destruction of such of the insects as might fall. A solution of one pound of common hard soap in five or six gallons of soft water, is used by English gardeners to destroy the young of the gooseberry sawfly; and the same was recommended to be tried upon the insects under consideration.
All the young of the saw-flies do not so closely resemble caterpillars as the preceding; some of them, as has already been stated, have the form of slugs or naked snails. Of this description is the kind called the slug-worm in this country, and the slimy grub of the pear-tree in Europe. So different are these from the other false caterpillars, that they would not be suspected to belong to the same family. Their relationship becomes evident, however, when they have finished their transformations; and accordingly we find that the saw-flies of our slug-worms and those of the vine are so much alike in form and structure, that they are both included in the same genus. Moreover, there are certain false caterpillars intermediate in their forms and appearance between the slimy and slug-like kinds and those that more nearly resemble the true caterpillars; thus admirably illustrating the truth of the remark, that nature proceeds not with abrupt or unequal steps;* or, in other words, that amidst the immense variety of living forms, wherewith this earth has been peopled, there is a regular gradation and connexion, which, in particular cases, if we fail to discover, it is rather to be attributed to our own ignorance and shortsightedness than to any want of harmony and regularity in the plan of the Creator. In considering the resemblances of species, we cannot fail to admire the care that has been taken, by almost insensible shades of difference among them, or by peculiar circumstances controlling their distribution, their habits of life, and their choice of food, to prevent them from commingling, whereby each species is made to preserve forever its individual identity.
The saw-fly of the rose, which, as it does not seem to have been described before, may be called Selandria Rosa, from its favorite plant, so nearly resembles the slug-worm saw-fly as not to be distinguished therefrom except by a practised observer. It is also very much like Selandria barda, Vitis, and pygmæa, but has not the red thorax of these three closely allied species. It is of a deep and shining black color. The first two pairs of legs are brownish gray or dirty white, except the thighs, which are almost entirely black. The hind legs are black, with whitish knees. The wings are smoky, and transparent, with dark brown veins, and a brown spot near the middle of the edge of the first pair. The body of the male is
* Natura saltus non facit. Linnæus. Syst. Nat. I. 11.
a little more than three twentieths of an inch long, that of the female one fifth of an inch or more, and the wings expand nearly or quite two fifths of an inch. These saw-flies come out of the ground, at various times, between the twentieth of May and the middle of June, during which period they pair and lay their eggs. The females do not fly much, and may be seen, during most of the day, resting on the leaves; and, when touched, they draw up their legs, and fall to the ground. The males are more active, fly from one rose-bush to another, and hover around their sluggish partners. The latter, when about to lay their eggs, turn a little on one side, unsheathe their saws, and thrust them obliquely into the skin of the leaf, depositing, in each incision thus made, a single egg. The young begin to hatch in ten days or a fortnight after the eggs are laid. They may sometimes be found on the leaves as early as the first of June, but do not usually appear in considerable numbers till the twentieth of the same month. How long they are in coming to maturity, I have not particularly observed; but the period of their existence in the caterpillar state probably does not exceed three weeks. They somewhat resemble young slug-worms in form, but are not quite so con
They have a small, round, yellowish head, with a black dot on each side of it, and are provided with twenty-two short legs. The body is green above, paler at the sides, and yellowish beneath; and it is soft, and almost transparent like jelly. The skin of the back is transversely wrinkled, and covered with minute elevated points; and there are two, small, triplepointed warts on the edge of the first ring, immediately behind the head. These gelatinous and sluggish creatures eat the upper surface of the leaf in large irregular patches, leaving the veins and the skin, beneath, untouched; and they are sometimes so thick that not a leaf on the bushes is spared by them, and the whole foliage looks as if it had been scorched by fire, and drops off soon afterwards. They cast their skins several times, leaving them extended and fastened on the leaves; after the last moulting they lose their semitransparent and greenish color, and acquire an opake yellowish hue. They then leave the rose-bushes, some of them slowly creeping down the stem, and others rolling up and dropping off, especially when the bushes are shaken by the wind. Having reached the ground, they burrow to the depth of an inch or more in the earth, where each one makes for itself a small oval cell, of grains of earth, cemented with a little gummy silk. Having finished their transformations, and turned to flies, within their cells, they come out of the ground early in August, and lay their eggs for a second brood of young. These, in turn, perform their appointed work of destruction in the autumn; they then go into the ground, make their earthen cells, remain therein throughout the winter, and appear, in the winged form, in the following spring and summer.
During several years past, these pernicious vermin have infested the rose-bushes in the vicinity of Boston, and have proved so injurious to them, as to have excited the attention of the Massachusetts Horticultural Society, by whom a premium of one hundred dollars, for the most successful mode of destroying these insects, was offered, in the summer of 1840. In the year 1832, I first observed them in gardens in Cambridge, and then made myself acquainted with their transformations. At that time they had not reached Milton, my former place of residence, and they did not appear in that place till six or seven years later. They now seem to be gradually extending in all directions, and an effectual method for preserving our roses from their attacks has become very desirable to all persons who set any value on this beautiful ornament of our gardens and shrubberies. Showering or syringing the bushes with a liquor, made by mixing with water the juice expressed from tobacco by tobacconists, has been recommended; but some caution is necessary in making this mixture of a proper strength, for if too strong it is injurious to plants; and the experiment does not seem, as yet, to have been conducted with sufficient care to insure safety and success. Dusting lime over the plants when wet with dew has been tried, and found of some use; but this and all other remedies will probably yield in efficacy to Mr. Haggerston's mixture of whale-oil soap and water, in the proportion of two pounds of the soap to fifteen gallons of water. Particular directions, drawn up by Mr. Haggerston himself, for the preparation and use of this simple and cheap application, may be found in the “ Boston Courier,” for the twenty-fifth of June, 1841, and also in most of our agricultural and horticultural journals of the same time. The utility of this mixture has already been repeatedly mentioned in this treatise, and it may be applied in other cases with advantage. Mr. Haggerston finds that it effectually destroys many kinds of insects; and he particularly mentions plant-lice, red spiders, canker-worms, and a little jumping insect, which has lately been found quite as hurtful to rose-bushes as the slugs or young of the saw-fly. The little insect, alluded to, has been mistaken for a Thrips or vine-fretter; it is, however, a leaf-hopper, or species of Tettigonia, and is described in a former part of this treatise.
According to the plan to which I have found it necessary to limit this work, only one more species of saw-fly remains to be described. Of the habits and transformations of this insect the late Professor Peck has given us an admirable account, under the title of a “ Natural History of the Slug-worm," which was printed in Boston, in the year 1799, by order of the “ Massachusetts Agricultural Society," and obtained the Society's premium of fifty dollars and a gold medal. own observations on this insect agree perfectly with those of Professor Peck, in the following remarks I have merely abridged and condensed his “Natural History of the Slugworm," a work now out of print, and rarely to be met with. It will be proper to premise that Professor Peck was inclined to believe this slug-fly to be a variety of the Tenthredo Cerasi of Linnæus, an insect found more commonly on the pear-tree in Europe than on the cherry, although it has a specific name derived from the latter tree. Most naturalists now reject the name given by Linnæus to the slimy grub of the pear-tree, because it is not strictly correct, and substitute a specific name imposed upon it by Fabricius. The European insect, therefore, is now called Selandria (Blennocampa) Æthiops ; and a good account of it, by Mr. Westwood, may be found in the thirteenth volume of “ The Gardener's Magazine.” It is possible that our slug-fly may have been imported from Europe,