Insect wing

“ An insect's wing is small at the base and broad at the end. This breadth would be useless near the body, because at this point the wing does not move swiftly enough to strike the air effectively. The type of the insectean wing is designed, then, simply to strike the air. But in the bird the wing plays also a passive role, i. e., it receives the pressure of the air on its under side when the bird is projected rapidly onward by its acquired swiftness. ”

“ But now we come to other species of birds that hunt in the air, chase their game on the wing, pursuing gnats and flies and butterflies, moths and mosquitoes and beetles. They require a short beak, but one that opens very wide and is pretty sure to catch insects as they fly—a beak, in fine, that may be depended on to work almost of itself and without an instant’s pause in the bird’s flight; a beak that, above all, is so sticky inside that as soon as an insect’s wing grazes this viscous lining it is caught [221] fast in the glue-like substance. ”

“ In those wings which, during the period of repose, are folded up beneath the elytra, the mere extension of the wing in the dead insect, where no injection of fluid can occur, causes the nervures to fall into position, and the membranous portions of the wing to unfurl or roll out precisely as in the living insect, and as happens in the bat and bird. ”

“ In no case are wings fully developed until the closing stage of the insect's life, they are always acquired after hatching or birth. We have already noticed (p. 40) how Sharp (1899) has laid stress on the essential difference between the exopterygote and endopterygote insects, the wing-rudiments of the former growing outwards throughout life while those of the latter remain hidden until the pupal instar. ”

“ Presently, the insect having mounted to the top of our finger, prepares for flight; its two hard cases fly up, and, behold! from beneath them appears a pair of the most beautiful gauze-like wings, [381] which it quickly unfolds, puts into motion, and then flies away. The two thick and horny covers for these delicate organs are called elytra, or "wing-cases." They are really the first pair of wings, much thickened; and their use is to protect the delicate membranous wings of the hinder pair, beneath them. ”

“ You see, the half of the wing next the body is stiff like a wing cover, and the other half is thin and silky, and folds up under the stiff part. When the insect flies it spreads out the under wings, too, for there is a pair of thin, flying wings folded on the body under these upper wings. ”

“ The wing of the May-fly flapping in the air is a respiratory organ, of as much importance to the wellbeing of the creature in its way, as the gill-plate of its grub prototype is when vibrating under the water. But the wing of the insect is not the only respiratory organ: its entire body is one vast respiratory system, of which the wings are offsets. The spirally-lined air-vessels run everywhere, and branch out everywhere. The insect, in fact, circulates air instead of blood. ”

“ I may, however, first observe that upon the expansion of the wings in flight, the insect has the voluntary power 45of making the inferior cling to the superior wing by a series of hooklets with which its anterior edge is furnished at about half the length of that wing, which gives to the thus consolidated combination of the two a greater force in beating the air to accelerate its progress. ”

“ It is now ascertained that the wings of insects are connected with the breathing apparatus, and that the respiration of the insect extends even to the very tips of these singular organs, which are not modifications of existing limbs, as in the birds, but additional structures. The circulation of insects may often be seen by placing a portion of a transparent wing under a moderately high power. ”

“ It is a curious circumstance, that if portions be removed from the posterior margins of the wings of a buzzing insect, such as the wasp, bee, blue-bottle fly, etc., the note produced by the vibration of the pinions is raised in pitch. This is explained by the fact, that an insect whose wings are curtailed requires to drive them at a much higher speed in order to sustain itself in the air. That the velocity at which the wing is urged is instrumental in causing the sound, is proved by the fact, that in slow-flying insects and birds no note is produced ”

“ This may be seen to some extent in our own species, for instance in the orange-tip of the Orange-tip, and the red bar in the upper wing of the Red Admiral (V. atalanta) . If we watch these insects, the conviction that these are true ornaments is soon forced upon us. The insect alights, perhaps alarmed, closes its wings, and becomes practically invisible. With returning confidence it will gradually open its wings and slowly vibrate them, then close them again, and lift the upper wing to disclose the colour. ”

“ Late in nymphal life a suture and a hinge-joint appear at the base of the wing, and thus there is some movement of the wing upon the notum; finally, the tracheæ are well developed in the wings, and numerous small sclerites are differentiated at the base of the wing, to which the 142special muscles of flight are attached, and thus the wings, after the last nymphal moult, have the power of flapping, and of sustaining the insect in the air; they thus become true organs of flight. ”

“ Another English naturalist, Professor Poulton, has suggested that the bright under wings lead the pursuing bird to catch the insect by them, the wing membrane giving way without serious injury to the moth. ”

“ They help themselves with the wings in jumping up at flying insects which they are pursuing. (Seen distinctly.)
5th. I think, but cannot be sure (and assurance is much needed) , that I saw once (Sept. 4th) a bird pursue a flying insect for a short distance on the wing, and near the ground. There was no doubt as to the chase on foot, and the flight came, or seemed to come, as part of such chase.
Not only were the actions of the birds whilst running (as described) exactly like those of the one I had seen catch the moths on Sept. ”

“ Although the figure-of-8 represents with considerable fidelity the twisting of the wing upon its axis during extension and flexion, when the insect is playing its wings before an object, or still better when it is artificially fixed, it is otherwise when the down stroke is added and the insect is fairly on the wing and progressing rapidly. In this case the wing, in virtue of its being carried forward by the body in motion, describes an undulating or spiral course, as shown in fig. ”

“ The insect youth are on the wing,
Eager to taste the honied spring,
And float amid the liquid noon; ”

“ Fair insect! that, with threadlike legs spread out,
And blood-extracting bill and filmy wing,
Does murmur, as thou slowly sail'st about,
In pitiless ears full many a plaintive thing,
And tell how little our large veins should bleed,
Would we but yield them to thy bitter need. ”

“ The wings and their structure The insects differ from all other animals except birds in possessing wings, and as we at the outset have claimed, it is evidently owing to them that insects are numerically so superior to any other class of animals, since their power of flight enables them to live in the air out of reach of many of their enemies, the greatest destruction to insect life occurring in the wingless larval and pupal stages. ”

“ From the shape of the wings in the butterfly or moth we can tell more or less how the insect flies. Long and narrow wings give a swift and rapid flight, broad round wings a slow and leisured flight.
The wings of insects are moved by only a few muscles, but with wonderful rapidity. It has been calculated that the common fly makes with its wings three hundred strokes per second, the bee one hundred and ninety. ”

“ A brown spotted lady-bug climbed the dizzy height of a grass blade, and Tom bent down close to it and said, "Lady-bug, lady-bug, fly away home, your house is on fire, your children's alone," and she took wing and went off to see about it —which did not surprise the boy, for he knew of old that this insect was credulous about conflagrations, and he had practised upon its simplicity more than once. ”

“ The front pair of wings, which alone were seen before they were expanded, became comparatively insignificant, while the hinder pair, which were before invisible, became the most prominent part of the insect, their translucent folds being coloured with the most brilliant hues, according to the species. The body seems to have shrunk as the wings have increased, and to have diminished to half its previous size, while the long legs that previously were so conspicuous are stretched out like the legs of a flying heron. ”

“ Turning our attention first to lower life, we find among insects some notable and instructive illustrations of abortive organs, and also of the ways and means through which the rudimentary conditions have been attained. In the beetle order, the natural or common condition of the wings—which in insects typically number four—is that whereby the first pair becomes converted into hardened wing-cases, beneath which the hinder and useful wings are concealed when at rest. ”

“ 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. ”

“ In this group the wings are generally held erect in repose, the under surface of the hind-wings and the apical portion of the under surface of the fore-wings being nearly always protectively coloured, these being portions of the wings exposed to view when the insect is at rest. There is an unusual amount of ornamental colouring on the upper surface. The flight is invariably diurnal. The larva has ten prolegs. ”

“ Sometimes their sharp hard wings almost swept his cheek as they wheeled round and round in circles, first narrow, then wide, and wider extending, till at last they soared far above the tallest tree-tops, and launching out in the high regions of the air, uttered from time to time a wild shrill scream, or hollow booming sound, as they suddenly descended to pounce with wide-extended throat upon some hapless moth or insect that sported all unheeding in mid-air, happily unconscious of the approach of so unerring a foe. ”

“ When one of these insects lies at rest, with its wings folded, among a number of leaves, it would be almost impossible to penetrate the disguise. This mimicry is no doubt an ingenious artifice to deceive the birds or other enemies that want to eat the insect. There is, however, one test which the cunning bird could apply: the leaves do not move about of their own accord, but the leaf-insects do. ”

“ These cases save the real wings from the damage which they might otherwise sustain, by rubbing or crushing against the sides of its abode; they serve also to keep the wings clean, and produce a buzzing noise when the animal rises in the air. The strength of this insect is astonishing; it has been estimated that, bulk for bulk, their muscles are a thousand times stronger than those of a man!
The beetle is only an insect disengaged from the pupa form; the pupa is a transformation in like manner from the worm or larva, and this proceeds from the egg ”

“ As soon as such expansions would be of even slight use to the insect as breathing organs, the question as to their permanency would be settled. Organs so useful both for flight and aëration of the blood would be still further developed, until they would become permanent structures, genuine wings. They would thus be readily transmitted, and being of more use in adult life during the season of reproduction, they would be still further developed, and thus those insects which could fly the best, i.e. which had the strongest wings, would be most successful in the struggle for existence. ”

“ Abdomen and posterior wings clay-coloured. Anterior ones brown orange, without any marks or lines thereon. Wings a little dentated; especially in the anterior wings. The larva of this insect is long, smooth, and shining, of a black colour, with eight longitudinal continuous yellow lines, with the base of the legs and a spot on the neck red. When alarmed it throws up its head and tail into the air. ”

“ Posterior wings with a dark narrow line rising on the anterior edges, which crosses the wings, meeting below the abdomen. A small black eye, with a white pupil, is placed near the middle of the anterior edges, and a row of faint oval dark spots runs parallel with the external edges, ending at the abdominal corners. This insect, like the last, flies exceedingly swift, and is observed sometimes to settle upon human excrement, a peculiar habit which is also adopted by other species of insects belonging to different orders. ”

“ Neither the grasshoppers nor the beetles are swift or particularly efficient, but they appear to demonstrate that the ordinary insect mechanism of flight is more effective with one pair of wings than with two. ”

“ Again, some winged insects have a sheath or shard for their wings, as the cockchafer; whereas in others the wings are unsheathed, as in the bee. But in the case of all alike, flight is in no way modified by tail-steerage, and the wing is devoid of quill-structure or division of any kind. ”

“ Bird and fly seem to know each other wonderfully well.
Here, then, we have a parasitical insect specialized in the highest degree, yet retaining all its pristine faculties unimpaired, its love of liberty, and of associating in numbers together for sportive exercises, and well able to take care of itself during its free intervals. And probably when thrown on the world, as when nests are blown down, or the birds get killed, or change their quarters, as they often do, it is able to exist for some time without avian blood. ”