Hessian fly

“ This movement through the water which is given to the artificial must be absolutely unlike any movement of the natural fly when under the surface; for in the natural fly, if it were not already drowned, the only possible movement would be that of its legs and wings, which, not being intended as a means of progression through the water, and being absolutely unsuitable for that object, would be most unlikely to enable it to do so. ”

“ Even if we assume that individual variations cropped up which had an instinct for slower flight, there would still, without selection, be no reason why this variation in particular should multiply, still less why the originally slight slowing of the flight should become more marked in the course of generations. On [Pg 154] the contrary, the butterflies fly a great deal, just as all other diurnal butterflies do; they exert their power of flight as long as the sun shines, and if the exercise of one generation influences the next, they ought to become gradually more capable of rapid flight. ”

“ However paradoxical it may seem, weight is necessary to aërial flight, and levity to subaquatic flight. A bird destined to fly above the water is provided with travelling surfaces, so fashioned and so applied (they strike from above, downwards and forwards) , that if it was lighter than the air, they would carry it off into space without the possibility of a return; in other words, the action of the wings would carry the bird obliquely upwards, and render it quite incapable of flying either in a horizontal or downward direction. ”

“ The appropriate stimulus to set the mechanism in motion is a light touch, while a more violent shock, or strong pressure, or a current of air, does not cause the trap to close. But if a fly comes to creep about on the leaf, and in doing so touches one of six short jointed hairs rising erect from a minute cushion of cells, then the leaf closes, quickly indeed, but at the same time so gently and imperceptibly that the fly is unaware of danger and does not try to escape. ”

“ Such birds do not expend their power so economically as the soaring birds. They do not pass much of their time in the air, but what time they are on the wing they put forth an immense amount of power and fly very rapidly, generally in a straight line, taking no advantage of air currents. ”

“ No argument could be more fallacious. The bird is a heavy, compact, by no means bulky body, and that trifle of heated air, or gas, if such were the case, but is [pg 26] not, which possibly might help elevation, would be but dust in the scale. A small balloon of two feet diameter—a larger body than any bird—can lift only about a quarter of a pound. But, besides, many admirable flyers, such as bats, have no air cells; while many animals, never intended to fly, are provided with them. ”

“ To tread upon the air (and this is what is really meant) is, at first sight, in the highest degree utopian; and yet there are thousands of living creatures which actually accomplish this feat. These creatures, however varied in form and structure, all fly according to one and the same principle; and this is a significant fact, as it tends to show that the air must be attacked in a particular way to ensure flight. It behoves us then at the outset to scrutinize very carefully the general configuration of flying animals, and in particular the size, shape and movements of their flying organs. ”

“ But in many cases this is not enough, namely, in all cases in which the degree of intelligence is not sufficiently high, or where the flight movement must follow so rapidly that it would be too late if it had to be regulated by the will, as, for instance, the shutting of the lids when the eye is threatened, or the flight of the fly or the butterfly when an enemy approaches. ”

“ The rapidity of travel of the insect wing is in some cases enormous. The wasp, for instance, is said to ply its wings at the rate of 110, and the common house-fly at the rate of 330 beats per second. Quick as are the vibrations of natural wings, the speed of certain parts of the wing is amazingly increased. Wings as a rule are long and narrow. As a consequence, a comparatively slow and very limited movement at the root confers great range and immense speed at the tip, the speed of each portion of the wing increasing as the root of the wing is receded from. ”

“ We shall never be able to imitate the flight of the soaring birds. We cannot hope to make a sensitive apparatus that will work quick enough to take advantage of the [24] rising currents of air, and he who seeks to fly has this problem to deal with. A successful flying machine, moving at a high velocity, is likely at any time to encounter downward currents of air, which will greatly interfere with its action. ”

“ It seems probable that most migratory journeys are performed at little more than the normal, unforced rate of flight, as this would best conserve the strength of the birds. Migrating birds passing lightships and lighthouses or crossing the face of the moon have been observed to fly without hurry or evidence of straining to attain high speed. The speed or rate of migration would therefore depend chiefly on the duration of flights and tail wind velocity. ”

“ Still, considering mere possibilities, it is not impossible that the twentieth century may be destined to make known natural forces which will enable us to fly from continent to continent with a speed far exceeding that of the bird. ”

“ THE COMMON FLY.—So many birds have been cited in support of the various flying theories that the house fly, as an example has been disregarded. We are prone to overlook the small insect, but it is, nevertheless, a sample which is just as potent to show the efficiency of wing surface as the condor or the vulture.
The fly has greater mobility than any other flying creature. By the combined action of its legs and wings it can spring eighteen inches in the tenth of a second; and when in flight can change its course instantaneously. ”

“ During the past few years reliable data on the speed of birds have accumulated slowly. It has been found that the common flying speed of ducks and geese is between 40 and 50 miles an hour, and that it is much less among smaller birds. Herons, hawks, horned larks, ravens, and shrikes, timed with the speedometer of an automobile, have been found to fly 22 to 28 miles an hour, while some of the flycatchers are such slow fliers that they attain only 1 to 17 miles an hour. Even such fast-flying birds as the mourning dove rarely exceed 35 miles an hour. ”

“ Thus, in flight, the air passes through the wing as it is raised, while in the downstroke the feathers are forced together to form a homogeneous surface.
Birds which fly much have the outer primaries of great length, giving the wing a pointed shape, as in swifts, while in species which fly but little, or frequent thickets, the outer primaries are very short, giving the wing a rounded appearance. ”

“ For, surely, there is a difficulty in explaining how the example of one vast body of birds, soaring forth on the morning flight, should not affect every individual of the still vaster body of which they form a part—the whole occupying, it must be remembered, a small and densely packed area—and why the impulse of the flying birds to fly should, apparently, become uncontrollable in each individual of them at the same instant of time. ”

“ Early experimenters in aviation observed that birds flapped their wings and flew. Accordingly they believed that man to fly must have wings and flap them likewise. Not for hundreds of years did they observe that most birds flapped their wings only to get headway, or altitude, thereafter soaring to great heights and distances merely by adjusting the angle of their wings to the various currents of air they encountered. ”

“ The size of the wing curves and air waves bear a fixed relation to each other, and both are dependent on the rapidity with which the wing is made to vibrate. This is proved by the fact that insects, in order to fly, require, as a rule, to drive their small wings with immense velocity. ”

“ These arguments are based on the belief that Nature never makes a mistake; that she made the bird to fly, and therefore the bird must be the most perfect model for the successful flying machine. But the truth is, the bird was not made primarily to fly, any more than man was made to walk. Flying is an incident in the life of a bird, just as walking is an incident in the life of a man. Flying is simply a bird’s way of getting about from place to place, on business or on pleasure, as the case may be. ”

“ Drag occurs when the artificial fly travels at a rate different from that of the natural fly in the same position—either faster or slower or with a tendency to move across or contrary to the current. It is caused by conflicting currents which exert dissimilar forces upon fly and line. ”

“ One day, however, the man lost his cast on the branches of a tree; this the native discovered and recovered, and, for a consideration, handed to my friend. "All's fair in love—and [Pg 191] fishing," so my friend sent the fly to his rod-and-tackle maker to be copied. The fly was unlike any fly my friend had ever seen, but he used it with marked success, and during the rest of his stay he used no other.
At Llanerfyl, a little village beyond Cann Office, I pulled up to inspect a long printed notice I observed on the church door there. ”

“ That birds which fly with flapping wings derive their support from the air, is undoubtedly true, and that the lift produced is due, not to the form, or shape, or area of the wing, is also beyond question. The records show that every conceivable type of outlined structure is used by nature; the material and texture of the wings themselves differ to such a degree that there is absolutely no similarity; some have concaved under surfaces, and others have not; some fly with rapidly beating wings, and others with slow and measured movements ”

“ This fact accounts for our seldom seeing some kinds of these flies abroad except females; and these are never seen to indulge in dances, flirtations, and games of chasing and buffeting each other, after the manner of so many kinds of flies. They habitually fly low; nevertheless they travel very great distances, for, though short, their flights are incessant when searching for their special kind of food.
The most disinclined to roam of all common flies is the stable-fly. None other is a more eager seeker of sunshine, but when basking on a sunny wall it seems unwary and sluggish ”

“ In the case of smaller birds or insects, such as the dragon-fly cited, it is an open question to what extent the problem is modified by the exigencies of active flight, and so the evidence, as confirming or otherwise the present theory, is at the best inconclusive. ”

“ Though it would not be true to say that hitherto writers on fly-dressing have shown any lack of power of observation, still it is unfortunately true that their energy seems, strangely enough, to have stopped short at observing the natural fly, and has not been sufficient to carry them on to making even passable imitations, except of Ephemeridæ. With the exception of this family of flies, no one could possibly recognise the artificial through knowing the natural fly which it is supposed to represent. ”

“ Thus, when the fly is so cast that it falls upon still or slow water while the line is allowed to rest upon swift water, the artificial fly will at once drag rapidly across or over the still place in an utterly unnatural manner. The natural fly would rest quietly upon such a place, or, if there were a slight current, float slowly downstream. ”

“ Of the FLY. After the Chrysalis has remained its due Time, the Fly bursts the Shell wherein it was contained, and comes out formed perfectly in every Part, except the Wings, which then appear too small to cover its Body. In this naked Condition it crawls up to some convenient Place, where its Wings may hang down without any Hindrance: And when thus disposed, the Wings begin to expand themselves so much, that in the Space of half an Hour, the Wings (of Butterflies) are stretched commonly to their full Size; nay, even those of the largest Moths seldom require above an Hour’s Time. ”

“ Even the numbers of these species which fly about indicates that they must be little decimated, and, in point of fact, we never find the wings of Heliconiidæ lying on the ground in the forests of South America, while those of the Nymphalidæ and other butterflies are by no means uncommonly seen as the remains of birds' meals. ”

“ But the house-fly, the kind that seems to be annoying you, my boy, isn’t so very old, certainly not much before the middle of the Age of Reptiles.”
“I wish their teeth or feet or something hadn’t developed properly,” the boy replied savagely, swatting at one that persisted in trying to settle on his nose. “Something ought to happen to make them die out.”
“Not much chance, I’m afraid,” the scientist responded wearily, “the fly isn’t particularly likely to die out soon. He squats on a baking rock in the equator and he perches on an ice-floe in the Arctic Circle. ”

“ It's all Nothing. We come, we go; and when we're done, we're done; Spiders and flies—we're mostly one or t'other— We come, we go; and when we're done, we're done." "By God, you sing that song as if you knew it!" Said I, by way of cheering him; "what ails ye?" "I think I must have come down here to think," Says he to that, and pulls his little beard; "Your fly will serve as well as anybody, And what's his hour? He flies, and flies, and flies, And in his fly's mind has a brave appearance; And then your spider gets him in her net, And eats him out, and hangs him up to dry. ”