There are two other circumstances in connexion with this part of our subject, which deserve noticing. If the reader will take into his hand a large blow-fly, and carefully examine its body with a lens near the spot where the wings are connected to it, he will succeed in discovering two organs of a curious kind. One of these, is a small membranous piece connected with the trunk-end of the wings, and is generally called the winglet, or alula. The other looks like a little drumstick hanging down, and is called the balancer, or poiser, or in Latin, the halter, or bridle. It is not clear of what use either of these organs is. Since the winglets are the largest in the heaviest bodies, and are altogether wanting in the lightest, it appears probable that one of their principal uses is to assist the wings during flight. If one might hazard the conjecture, perhaps they act like the parachute of a balloon. As to the so-called balancers, it has been considered that they serve to poise the insect while flying. Dr. Derham considered that they kept the body steady during flight; and he states that if either a poiser or a winglet is cut off, it will fly awkwardly and unsteadily, as if it had lost some very necessary part. Another observer states, that he cut off the winglets of a fly, leaving both its wings and poisers; but it could no longer fly. He also cut off, in another fly, the poisers alone, and the same result took place. On cutting off both the poisers of a crane-fly, he says it was unable either to fly or walk.[Y] Mr. Westwood says he has seen the poisers beat rapidly upon the winglets like drumsticks on a drum, and it has been supposed that this action is the cause of the hum made by the insect in flying. This is doubtful, because it has been found that after the winglets are cut away the humming sound is still produced; and some humming insects have no winglets.
So much importance did Linnæus, the great father of natural history, attach to the character of the wings in insects, that he arranged the various families of insects under several heads expressive of the leading character of their wings. The orders into which he thus divided insects are seven in number: 1. Coleoptera, or case-winged; 2. Hemiptera, or half-winged; 3. Lepidoptera, or scale-winged; 4. Neuroptera, or nerve-winged; 5. Hymenoptera, or membrane-winged; 6. Diptera, two-winged; and, 7. Aptera, or wingless: the Greek word pteron, signifying "a wing," furnishes the termination to each of these titles; the prefix is also derived from the Greek, and its import may be derived from the translation attached to each. This system has been extended by modern entomologists, who have subdivided the 2d, 5th, and 7th orders into additional ones.
In the opposite cut the insects represented illustrate each of the Linnæan orders. They are—1. a Beetle; 2. an Aphis; 3. a Butterfly; 4. a Bee; 5. a Dragon-fly; 6. a House-fly; and, 7. a Spider.
As these organs exhibit to us in the most conspicuous manner the exquisite beauties wherewith it has pleased God, the Almighty Creator, to adorn the insect world, we may be allowed to make some reference to the colours of the wings, before proceeding to speak of those organs by which the insect moves on earth. Some, of the beetle tribe, are like tiny masses of burnished metal gleaming with colours of the most exquisite description. A vast number of locusts are remarkable for the splendour of their wings. Many dragon-flies are adorned with wings vying with those of the butterfly in loveliness. The wings of many flies are exquisitely painted with the most brilliant metallic hues, green and gold; and even those of a house-fly are often very beautiful by their having the property of iridescence, or reflecting the prismatic colours of light. But insects of every tribe, however splendid in attire, fade before the glories of the butterfly tribe. Linnæus, speaking of the splendid colours of these insects, and particularly of the gorgeous tints which appear on the upper surface of the wings of a butterfly called the Morpho Menelaus, and another, justly observes, that there is scarcely anything in nature that for brightness and splendour can be paralleled with this colour. It is a kind of rich ultramarine, that vies with the deepest and purest azure of the sky; and what must cause a striking contrast in flight, the prone surface of the wings is as dull and dark as the opposite is brilliant; so that one can conceive this insect to appear like a planet in full radiance, and under eclipse, as its wings open and shut in the blaze of a tropical sun. The scales on the wings of some species shine with such extraordinary intenseness and brilliancy, that it is impossible to look at them in a bright light, as they completely dazzle the beholder. Messrs. Kirby and Spence say, they "know no insect upon which the sight rests with such untired pleasure as upon the lovely butterfly that bears the name of the unhappy Trojan king (Papilio Priamus); the contrast of the rich green and black of the velvet of its wings with each other, and with the black of its abdomen, is, beyond expression, regal and magnificent." What adds to the beauty of the wings of this tribe of insects is the appearance of the beautiful spots like eyes, which are so familiar to us, and which are almost without a parallel, except in the animal world. This ornament gives to the wings of a butterfly an indescribable life and beauty, and constrains us as we contemplate it to acknowledge that 'Solomon, in all his glory, was not arrayed like one of these.' The astonishing variety of combination in the colours communicates an inexpressible charm to these insect glories: here is a lustrous blue, a glowing orange, a delicate lemon, an exquisite pink, a fiery copper, or a spotless white. None but a Divine hand could have produced such effects as are exhibited in these most gorgeously painted organs. No work of man will endure comparison with them. The most elaborately finished miniature upon which the artist may, in the features and dress of the person, have expended all the resources of his art in the production of harmonious and pleasing tones of colour, appears but as a muddy, lustreless patch, when placed side by side with one of the butterfly-beauties of the tropics, or even of our own green fields.
Hind Leg of a Bee.
We must not, however, allow the fascination of these beautiful objects to engross our whole attention; and it is now time for us to state some particulars connected with the legs of the imago, or perfect insect. Six is the true number of legs which belong to the insect in the imago state. They are connected to its body at the thorax, and are formed of a series of minute tubes, provided internally with muscles and nerves. They are commonly divided into four parts; a the haunch, b the thigh, c the tibia, and d e the foot.
The front pair of legs, or, as they are generally called, the forelegs, are considered by some authors to be really the insect's arms, the last portion of them being the hand. Certainly they are often as useful to the insect as is this admirable organ to ourselves; not only are they serviceable in walking, but they also enable the insect to climb, to lay hold of various objects, or to catch their prey, to dig in the earth, and in many instances to clean the head and face of the creature; an operation in which many of them, and particularly flies and bees among our domestic insects, are most praiseworthily particular; having apparently an aversion to nothing so much as to a dirty face and unbrushed jacket! The other pairs of legs are altered in various manners in order to fit them for the different purposes for which they are required by the insect.