All the insects represented in these two plates belong to the genus Libellula of Linnæus, or the family of Dragon-flies, Libellulidæ. When the original edition of this work was published, there was no English work in which the natural history and curious transformations of this tribe of insects were detailed. Our author, therefore, in order to supply the deficiency, published the following interesting series of observations upon the subject:—
"As I have not met with any English author who has given the natural history of the insects delineated in these two plates, I shall make no apology for its introduction; the frequent opportunities I have had of observing their mode of life and action, together with the many singular circumstances observable in both, being motives for its publication too powerful to be resisted.
"It is not easy to determine whether they should be ranked among the water insects, or those of the land, nor shall I attempt here to ascertain it; my present business being only to relate the several circumstances attending them during their respective states in which they are passing from the egg to the complete animal: and although these observations have been confined to our English ones, yet they so exactly agree and coincide with those of foreign countries, (as my correspondents have assured me), that their nature and behaviour appear to be just the same; so that what is observable in ours, is at the same time applicable to the whole genus wherever found.
"If we take a cursory view of the different ranks of animals that inhabit our globe, we shall hardly find one that can excite our wonder and astonishment more than this genus; nor is it from that general ignorance of the insect world, that reigns so strongly in these kingdoms, that I am emboldened to say this; but if we reflect that the beasts, birds, and reptiles are furnished with powers for living only in the air, and that even the amphibious tribes can perform the office of respiration only in that element: if we also consider that fishes, on the contrary, are unable to respire but in water, and when deprived of that must certainly perish, we cannot but conclude that all these animals are most wisely fitted with means and faculties for filling up the respective orders and ranks wherein they are placed. But let us cast our eyes on the subjects I am about to describe, and there behold a tribe of beings, who, as soon as they leave their eggs, subsist for a certain number of months, (I had almost said years), creeping and swimming in the liquid element; are there invested with organs and powers for existing and weathering out the utmost severity and intemperance of the winter; that afterwards as the spring and summer advances, and the period arrives when they are to appear in other forms, in the space of about half an hour those very organs and powers that before enabled them to live under water should be so entirely altered, the very natures and abilities of the creatures so changed as to permit them to quit their former element and place of residence, insomuch that all the remaining part of their lives is spent in the open air, furnished with wings, and flying about in the full glee of wanton liberty; that in a very few weeks after, having performed the business of generation, the same animals should die of mere old age, with their wings quite ragged and worn out, their strength exhausted, and all the powers of their bodies lost by a total imbecility and weakness, which but a little before enabled them to transport themselves through the air with the swiftness of a bird. If, I say, we reflect on all these circumstances, we cannot but allow them to be objects of a very extraordinary nature, and well adapted for leading the mind to the contemplation of their supreme Author, who has thought proper to exhibit to us these kind of insects, thus differing from almost all the animals in the creation.
"They have been variously named by different authors, owing perhaps to the time when they wrote, or the progress natural history had made in the world. Some have called them by the name of Dragon Fly, others Adder Bolt, Balance Fly, Perla, Libellula or Libella. I shall prefer the last, as conveying an idea well known to English adepts. The caterpillars of them all live in ponds and stagnant waters (that are undisturbed by cattle) during the greatest part of their lives, and make their appearance under three general forms. The first is shewn by Fig. 1. 1.; the second by Fig. 2.; and the third by Fig. 3. See Plate [47]. As these are the shapes in which they all appear, it will not be improper to mention each particularly.
"The two caterpillars at Fig. 1. 1. Plate [47], belong only to or produce those that sit at rest, with their wings erect, (see Plate [48]. Fig. 2.), and differ from both the others not only in size but in the roundness and slenderness of their bodies; at the extremity whereof they are furnished with three tails, each of which upon examination being found to be a kind of feather, and is an appendage that neither of the others have. Their behaviour also in the water is different from the others, being enabled to twist and bend their bodies in a more circular manner. [Subfamily Agrionides.]
"The second sort of caterpillars, at Plate [47]. Fig. 2. are much shorter and thicker in their bodies than either of the others, producing those Libellas with flat bodies, as Plate [47]. Fig. 4. and 6. and Plate [48]. Fig. 1. and 5. These are, of all others, the most disagreeable in their appearance; most of them having their bodies and legs very rough and shaggy, and of the exact colour of mud. Others appear of a dirty green, and very unpleasing hue, a colour that in general reigns among them all; for none can boast of any beautiful appearance while in this state, unless the different shapes here exhibited can be called so. Indeed the beauty and symmetry, so apparent in their complete states, make ample amends for the want of it in this; all of them in general being then very beautiful, discovering colours superior to art. [Subfamily, Libellulides. Genus, Libellula.]
"The caterpillars of the third sort (see Plate [47]. Fig. 3.) are very different from the preceding, being the size of the figure, with the abdomen flat at bottom and rounding at top, longer and slenderer than those at Fig. 2. but not so much as those at Fig. 1. 1. These produce those large Libellas with long slender bodies, who sit at rest with their wings expanded, as Plate [47]. Fig. 5. [Subfamily, Libellulides. Genus, Æshna.]
"Under these three forms are all the caterpillars of Libellas found, there being but little difference in the colours or marks of the respective tribes; the various sizes and shapes being the chief observable circumstances attending them. They are all furnished with six legs, and have each of them four little membranaceous substances issuing from the back, or upper part of the thorax, that are the follicles, or cases, wherein the wings are inclosed. When the young caterpillars issue from their confinement in the eggs, there is no appearance of these cases, nor till a considerable time after; but as they arrive to a maturer state they become more conspicuous, and, like the young leaves of trees that open and expand themselves on the arrival of the spring, their appearance increases, till having approached the period when they are to forsake their former habitations and become inhabitants of the air, these wing-cases have then arrived to their due size, and carry the appearance in which they are here seen. They are all of them, from the largest to the smallest, armed with a strong offensive weapon, which serves them, and is indeed the means they are endued with, for obtaining their food. This weapon being placed in the under part of the head, just beneath the mouth, I have displayed in Fig. 1. and 3. of Plate [47]. where it appears just in the same manner as when they are endeavouring to catch their prey. In the largest figure at 1. and also in Fig. 2. it appears contracted and shut up, as when at rest. The strength and power that these animals discover in the use of this instrument is very singular and extraordinary. There are two joints to it, one about the middle, the other underneath the mouth, close to the throat; and in some (particularly all those of Fig. 2.) when it is closed or contracted, it appears fastened to the face of the creature, by fitting it so exactly as to form a perfect mask; covering the mouth, and reaching almost as high as the eyes. In others it is made to fit only the under part of the mouth, and when at rest is drawn up close underneath it. At the extremity of those that are extended may be observed two very strong and remarkable fangs; that, shutting over each other, form a pair of forceps, of such strength that few, if any of their captives, can escape if once inclosed therein. [This organ is the greatly developed lower lip of the larva, and is analogous in its structure to the same part in the imago.]