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Les diagrammes suivants iiiustrant la mAthode. 1 2 3 1 2 3 4 5 6 V* FLASHLIGHTS ON NATURE 4 / FLASHLIGHTS ON NATURE BY GRANT ALLEN AUTHOR OF " The Story of the Plants " " Evolution of the Idea of God,'' etc. ILLUSTRATED BY FREDERICK ENOCK NEW YORK DOUBLEDAY & MCCLURE CO 1898 COPYRIGHT, 1898, BY DOUBLEDAY AND MCCLURE CO. CONTENTS AND ILLUSTRATIONS THE COWS THAT ANTS MILK A BRANCH OF THE FAMILY TREE WOUN-OUT MOTHER . BUPDING MOTHER . WINGED FEMALK UNNATURAL LODGER A TRAGIC ENEMY AN ANT MILKING A ROSE APHI A COMIC ENEMY A PLANT THAT MELTS ICE LEAVES OF SOLDANELLA . BUD BEGINNING TO MELT ITS WAY UP BUD ENCLOSED IN A GLOBE OF AIR FLOWER REACHING SURFACE OF ICE FLOWER VISITED BY A BI.E A GROUP OF FLOWERS PROTRtJDING THROL'G A PAIR OF FLOWERS WHICH HAVE FAILED A BEAST OF PREY COCOON OF YOUNG SPIDERS YOUNG SPIDEKLINGS CASTING FIRST THREADS BABY SPIDER IN ITS FIRST SNARE . ROSALIND'S SPINNERETS .... FOOT, CLAWS, AND FACE OF SPIDER ROSALIND ON HER WAY TO BLOW-FLY ROSALINr TRUNDLING BLOW-FLY A SPIDER CHANGING ITS CLOTHES . ROSALIND AND HER SUITORS . V ICE PAGB I 3 5 9 II 12 14 i6 21 25 33 34 35 36 37 39 41 47 49 52 53 56 57 62 63 65 67 VI CONTENTS AND ILLUSTRATIONS A WOODLAND TKAOKDY THE BUTCHKR-BIKI) .... THE BUTCIIER-BIKD'.S Will, PART OK HIS LARDER HIS WIFE IMPALING A IIARVKS l-MOUSE BEETLES ANO FIELD-MOUSE " I WANT THAT FLY "... THE WIFE ON HER NEST . MARRIAGE AMONG THE CLOVERS FEMALE BEGONIA FLOWERS THE SEED-BAG . FLOWERS IN BUD MALE FLOWER, FRONT VIEW MALE FLOWER, BACK VIEW DUTCH CLOVER IN SIX ASPEC'I S STRAWBERRY CLOVER IN FIVE ASPECTS THOSE HORRID EARVvIGS PORTRAIT OF A GENTLEMAN PORTRAIT OF A LADY WITH WTNGS EXPANDED . BEGINNING TO CLOSE SEVEN FURTHER STAGES . THE TAIL HELPS THE USE OF IHE PINCERS THE TAIL SIRAIGHIENED AGAIN THE WING BENKATH THE WING-CASE THE WING-v ASK RAISED . SITTING ON HER EGGS HER BROOD OF CHICKS . CAMPODEA .... THE earwig's MOUTH rAGB 71 74 75 76 79 84 86 87 94 96 98 99 100 lOI 105-113 iiS-"9 121 124 125 128 129 30-136 137 138 139 140 141 142 '43 144 145 THE FIRST PAPER-MAKER 148 FAMILY PORTRAITS ISO THE CITY, TWO DAYS OLD 156 THE CITY, FIVE DAYS OLD 157 CONTENTS AND ILLUSTRATIONS Vll THE CITY, FIFTEEN DAYS OLD NEST OK TRKE WASP, TWO ASPECTS wasp's head in five ASPECTS QUEEN WASP WITH FOLDED WINOS PART OF TWO WINGS THE POISON-BAG ... DARTS MAGNIFIED THE wasp's BRUSH AND COMB TUCKS IN THE SEGMENTS ABIDING CITIES A WOOD ANTS' NKST, EXTERIOR A WOOD ants' NEST, INTERIOR "let's GO slave-hunting" . A slave-hunt .... PAYING OFF OLD SCORES . A LONG PULL AND A STRONG PULL THE GARDEN ANT . HEAD OF GARDEN ANT THE ant's BRUSH AND COMB . A FROZEN WORLD THE GREAT POND-SNAIL IN SUMMER THE GREAT POND-SNAIL IN WINIER THE CURLED POND-WEED PRODUCING SHOOTS THE SHO )TS BEFORE, DURING, AND AFTER FROST THE WHIRLIGIG BEETLE DANCING AND SLEEPING '.HE FROGBIT IN SUMMER AND WINTER ITS BUDS RISING IN SPRING .... BRITISH BLOODSUCKERS .... THE mosquito's EGG-RAFT, IN TWO ASPECTS . THE EGGS HATCHING AND YOUNG ESCAPING . THE MOSQUITO LARVA STANDING ON HIS HEAD THE larva's BREATHING-TUBE THE CHRYSALIS BREATHING .... THE MOSQUITO EMERGES .... AND MAKES A BOAT OF HER OLD SKIN . PAf'.B 164, 165 168-172 '74 •75 176 176 177 179 186 181 186 189 190 191 194 196, 197 "99 204 212 213 214 215-217 221, 223 225, 227 229 . 232 236, 237 . 238 239 241 242 244 246 Vlll CONTENTS AND ILLUSTRATIONS HEADS OF MOSyUITOES THK GADFLY .... HIS LANCKTS .... AND TIIKIR CUTTINi; KDGKS . A VERY INTELLIGENT PLANT THE BABY GORSE PLANT . AT ONE WEEK OLD . OUTGROWING ITS INFANT STAGE THE YOUNG SHRUB BEGINS TO ARM ITSELF THE GENISTA .... THE BROOM .... PROTECTING THE KUDS . THE GRKAT-COAT THE FLOWER, HALF OPKNtD . DISCHARGING POLLEN-SHOWERS THE POD, WITH BEANS . THE POD, AFTER DISCHARGING BEANS . A FOREIGN INVASION OF ENGLAND AN INVALID BARLEY PLANT . THE SOURCE OF THE MISCHIEF THE GRUB AT WORK SEVEN WELL-FAVOURED EARS SEVEN LEAN EARS . THE GRUB TURNING ROUND THE CLIMBING PUPA. THE PUPA COMES OUT AND THE FLY COMES OUT OF IT ANTENN/« FREE ! V INGS FREE ! . . . NOW FOR THE LEGS ! THE LAST PULL HANGING HERSELF UP TO DRY WILY ENEMY LAYING HER EGGS PAC.I 254 258 262 263 266 267 26S 269 270 271 276 277 280 281 284 288 289 290 292 293 29s 299 300 301 302 303 304 30s 306 311 FLASHLIGHTS ON NATURE THE COWS THAT ANTS MILK DON'T let my title startle you ; it was Linnaeus himself who first invented it. Everybody knows the common little "green-flies" or " plant-lice " that cluster thick on the shoots of roses ; and most people know that these trouble- some small insects (from the human point of view) are the true source of that shining sweet juice, rather slimy and clammy, that covers so many leaves in warm summer weather, and is com- monly called honey-dew. A good many people have heard, too, that ants use the tiny green crea- tures in place of cows, coaxing them with their feelers so as to make them yield up the sweet and nutritious juice which is the ants' substitute for butter at breakfast. But comparatively few are aware how strange and eventful is the brief life- history of these insignificant little beasts which we destroy by the thousand in our flower-gardens or conservatories with a sprinkle of tobacco -water. A Flashlights on Nature To the world at large, the aphides, as we call them, are mere nameless nuisances — pests that infest our choicest plants ; to the eye of the naturalist, they are a marvellous and deeply interesting group of animals, with one of the oddest pedi- grees, one of the qi eerest biographies, known to science. I propose, therefore, in this paper briefly to recount their story from the cradle to the grave ; or, rather, to be literally accurate, from the time when they first emerge from the egg to the moment when they are eaten alive (with some hundreds of their kind) by one or other of their watchful ene- mies. In this task I shall be aided not a little by the clever and vivid dramatic sketches of the Aphides at Home, which have been prepared for me by my able and watchful collaborator, Mr. Frederick Knock, an enthusiastic and observant naturalist, who thinks nothing of sitting up all night, if so he may catch a beetle's egg at the moment of hatching ; and who will keep his eye to the microscope for twelve hours at a stretch, relieved only by occasional light refreshment in the shape of a sandwich, if so he may intercept some rare chrysalis at its moment of bursting, or behold some special grub spin the silken cocoon wi hin whose case it is to develop into the perfect winged insect. Rose-aphides, or " green-flies," as most people call them, are, to the casual eye, a mere mass of living " blight " — a confused group of tiny trans- The Cows that Ants Milk 3 lucent insects, moored by their beaks or sucking- tubes to the shoots of the plant on which they have been born, and which they seldom quit unless forcibly ejected. For they are no Columbuses. The spray of rose-bush figured in sketch No. i shows a small part of one such numerous house- hold in quiet possession of its family tree and NO. I, — A BRANCH OF THE FAMILY TREE. engaged, as is its wont, in sucking for dear life at the juices of its own peculiar food-plant. You will observe that they are clustered closest at the growing-point. Each httle beast of this complex family is coloured protectively green, so as to be as inconspicuous as possible to the keen eyes of its numerous enemies ; and each sticks to its chosen twig with beak and sucker as long as there is any- Flashlights on Nature thing left to drink in it, only moving away on its six sprawling legs when its native spot has been drained dry of all nutriment. We often talk metaphorically of vegetating : the aphis vegetates. Indeed, aphides are as sluggish in their habits and manners as it is possible for a living and locomotive animal to be : they do not actually fasten for life to one point, like oysters or barnacles ; but they are born on a soft shoot of some particular plant ; they stick their sucking-tube into it as soon as they emerge ; they anchor them- selves on the spot for an indefinite period ; and they only move on to a new "claim" when sheer want of food or force majeure compels them. The winged members are an exception : they are founders of new colonies, and are now on iheir way to some undiscovered Tasmania. And, indeed, as we shall see, these stick-in-the- mud creatures "lave yet, in the lump, a most event- ful history — a history fraught with strange loves, with hairbreadth escapes, with remorseless foes, with almost incredible episodes. They have enemies enough to satisfy Mr. Rider Haggard or the British schoolboy. If you look at No. 2, you will see the first stage in the Seven Ages of a rose-aphis family. The cycle of their life begins in autumn, with the annual laying of the winter eggs ; these eggs are carefully deposited on the leaf-buds of some rose- bush, by a perfect wingless female, at the first approach of the cold weather. I say a perfect wingless female, because, as I shall explain here- The Cows that Ants Milk 5 after, most aphides (and especially all the summer crops or generations that appear with such miracu- lous rapidity on our roses and fruit-trees) are poor fatherless creatures ; waifs and strays, budded out vegetatively like the shoots of a plant. About this strange retrogressive mode of reproduction, however, I shall have more to tell you in due time by-and-by ; for the pre- sent, we will confine ourselves to the im- mediate history of the autumn brood, which is regularly produced in the legitimate fashion, as the result of an or- dinary insect marriage between perfectly de- veloped males and females. As October approaches, a special generation of such per- fect males and females is produced by the un- wedded summer green-flies ; and the females of this brood, specially told off for the purpose, lay the winter eggs, which are destined to carry on the life of the species across the colder months, when NO. 2.— WORN-OUT MOTHER- LAYING HER LAST EGG. r 6 Flashlights on Nature no fresh shoots for food and drink are to be found in the frozen fields or gardens. The eggs, so to speak, must be regarded as a kind of deferred brood, to bridge over the chilly time when living aphides cannot obtain a livelihood in the open. In No. 2 we see, above, a rose-twig with its leaf-buds, which are undeveloped leaves, inclosed in warm coverings, and similarly intended to bridge over the winter on behalf of the rose-bush. On this twig, then, we have the winter eggs of the aphis, mere dots represented in their natural size ; they are providently laid on the bud, which in early spring will grow out into a shoot, and thus supply food at once for the young green-flies as they hatch and develop. So beautifully does Nature in her wisdom take care that blight in due season shall never be wanting to our Marshal Niels and our Gloires de Dijon ! In the same sketch, too, we have, below, a pathetic illustration, greatly magnified, of the poor old worn-out mother, a martyr to maternity, laying her last egg in the crannies of the bud she has chosen. I say "a martyr to maternity" in solemn earnest. You will observe that she is a shrivelled and haggard specimen of over-bur- dened motherhood. The duties of her station have clearly been too much for her. The reason is that she literally uses herself up in the pro- duction of offspring ; which is not surprising, if you consider the relative size of egg and egg-layer. When this model mother began to lay, I can assure The Cows that Ants Milk 7 you she was fat and well-favoured, as attractive a young green-fly as you would be likely to come across in a day's march on the surface of a rose- twig. But once she sets to work, she l:iys big eggs with a will (big, that is to say, compared with her own size), till she has used up all her soft internal material ; and when she has finished, she dies — or, rather, she ceases to be ; for there is nothing left of her but a dried and shrivelled skin. During the winter, indeed — in cold climates at least — the race of aphides dies out altogether for the time being, or only protracts an artificial exist- ence in the heated air of green-houses and drawing- rooms. The species is represented at such dormant periods by the fertilised eggs alone, which lie snug among the folds or scales of the buds till March or April comes back again to wake them. Then, with the first genial weather, the eggs hatch out, and a joyous new brood of aphides emerges. And here comes in one of the greatest wonders ; for these summer broods do not consist, like their parents in autumn, of males and females, but of imperfect mothers — all mothers alike, all brother- less sisters, and all budding out young as fast as they can go, without the trouble and expense of a father. They put forth their progeny as a tree puts forth leaves, by mere division. The new broods thus produced are budded out tail first, as shown in No. 3, so that all the members of the family stand with their heads in the same direction, the mother moving on as her offspring increases ; 8 Flashlights on Nature and since each new aphis instantly begins to fix its proboscis into the soft leaf-tissue, and in turn to bud out other broods of its own, you need not wonder that your favourite roses are so quickly covered with a close ^ayer of blight in genial weather. To say the truth, the rate of increase in aphides is so incredibly rapid, that one dare hardly mention it without seeming to exaggerate. A single in- dustrious little green-fly, which devotes itself with a quiet mind to eating and reproduction, may easily within its own lifetime become the ancestor of some billions of great-grandchildren. It is not difficult to see why this should be so. The original parent buds out little ones from its own substance at a prodigious rate ; and each of ^hese juniors, reach- ing maturity at a bound, begins at once to bud out others in turn, so that as long as food and fine weather remain the population increases in an almost unthinkable ratio. Of course, it is the ex- treme abundance of food and the ease of living that result in this extraordinary rate of fertility ; the race has no Malthus to keep it in check — each aphis need only plunge its beak into the rose-shoots or leaves and suck ; it can get enough food without the slightest trouble to maintain itself and a nume- rous progeny. It does not move about recklessly, or use up material in any excessive intellectual effort ; all it eats goes at once to the production of mere and more aphides in rapid succession. Many things, however, conspire to show that The Cows that Ants Milr ^ins to fix id in turn 1 need not so quickly in genial in aphides ly mention single in- itself with may easily tor of some lot difficult ;inal parent stance at a iors, reach- to bud out id and fine ises in an is the ex- e of living )f fertility; heck — each rose-shoots )od without nd a nume- recklessly, intellectual production ession. show that aphides did not always lead so slothful a life : they are creatures with a past, the unworthy des-^endants of higher insects, which have de- generated to this level through the excessive abundance of their food, and through their adop- tion of what is prac- tically a parasitic habit. When life is too easy, men and insects in- variably degenerate : struggle is good for us. One of these little indi- cations of a higher past Mr. Enock has given us in the upper part of sketch No. 3. For some members of the brood go through regular stages of grub and chrysalis, like any other flies ; or, if you wish to be accurately scientific, pass througn the usual forms of larva and pupa, before they reach the full adult con- dition. This, of course, shows them to be the descendants of higher insects which underwent the common metamorphosis of their kind. But most of the budded-out, fatherless broods in summer are NO. 3. — BUDDING MOTHER — PRODUCING A FATHERLESS BROOD lO Flashlights on Nature : ! s h ;? produced ready-made, without the necessity for passing through larval or infantile stages. Or rather, they never grow up : they merely moult ; and they produce more young while they are still larvae. They are born fully formed, and proceed forthwith to moor themselves, to feed, and to bud out fresh generations, without sensible interval. In No. 3 we have various stages in the development of the spring brood. Above we see the pupa, or chrysalis, produced from a grub (not very grub-like in shape), which has sprung from an egg ; and on the right, below, we see the shrivelled larval skin from which it has just freed itself. This particular aphis was thus born as a six-legged larva from an autumn egg ; it passes through the intermediate form of a pupa, or chrysalis ; and it will finally develop into a winged "viviparous" female, such as you see in No. 4 below, putting out its young alive as fast as ever its wee body can bud them. You may observe, however, that in the case of aphides there is no great difference of form between the three successive stages. Larva, pupa, and fly are almost identical. In No. 4, again, we have a portrait from life of such a winged female, the mother of a numerous fatherless progeny ; for both winged and wingless forms are produced through the summer. She is round and well-fed, as becomes a matron. Observe in particular the curious pair of tubes on the last few rings of her back ; these are the organs for secreting nectar or honey-dew^ a point about which The Cows that Ants Milk II ty for 5. Or moult ; re still iroceed to bud al. In )pment Lipa, or ub-like and on 'al skin rticular rom an mediate I finally le, such young i them, case of :)etween and fly life of imerous vingless She is Dbserve the last ;ans for t which I shall have a good deal more to say presently. A winged female like this may fly away to another rose-bush to become the foundress of a distant colony. The same illustration also shows, in a greatly enlarged form, her beak or sucking appa- ratus, which con- sists of four sharp lance - like siphons, enclosed in a pro- tective sheath or proboscis, and ad- mirably adapted both for piercing the rose-twig and for draining the juices of your choicest crimson ramblers. The aphis sticks in the point as if it were a needle, and then sucks away vigorously at the rose-tree's life-blood. You can watch her so any day with a common small mag- nifier, and see how, like the lady at Mr. Stiggins' tea meeting, she "swells wisibly" in the process. Indeed, aphides are always beautiful objects for the microscope or pocket lens, with their pale, trans- parent green bodies, their bright black eyes, their NO. 4. — WINGED FEMALE— THE FOUNDRKSS OF A COLONY. 12 Flashlights on Natt^re km ft ! jointed liairy legs, their delicate feelers, and their marvellous honey-tubes ; and it will not be my fault if you still continue to regard them as nothing more than the " nasty blight" that destroys your roses. Do not for a moment suppose, however, that you and your gardener, with his spray and his tobacco-water, are the only en.mies the rose- aphis possesses. The name of her foes is legion. She is devoured alive, from with- out and from within, by a ceaseless horde of aggres- sive belligerents. The most destructive of these enemies are no doubt the lady-birds, which, both in their larval and their winged forms, live almost entirely on various kinds of green-fly. This prac- tical fact in natural history is well known to hop- growers, for the dreaded " fly " on hops is an aphis ; its abundance or otherwise governs the hop markt', and Kentish farmers are keenly aware that a certain particular lady-bird eats the "fly" by millions, on which account they protect and foster the lady-bird, NO 5.— UNNATURAL LODGER EATS HIS HOSTESS OUT OF HER SKIN. The Cows that Ants Mh.k 13 I their y fault I more ►ses. lomeiit , that rdener, ,ul his he only ;-aphis ame of She is m with- in, by a aggres- The )f these ubt the both d their almost IS kinds s prac- history ) hop- dreaded aphis ; markt', certain ons, on dy-bird, llius leaving tlie two insects, tlie parasite and the carnivore, to light it out in their own way Ix'tween them. But No. 5 introduces us to a still more insidious though less dangerous foe : an internal parasite which lays its eggs inside the body of the bud- producing female. There the grub hatches out, and proceeds to eat up its unwilling hosiers, alive, /rom ivithin. l.i the sketch, we have an illustration, below, of an aphis which has thus been compelled to take in a stranger to board and lodge in her stomach ; while the top figure shows how the lodger, after eating his hostess out, eats himself out into the open air through her empty skin. If you look out closely for such haunted green-flies, in- habited by a parasite — most often an ichneumon fiy — you will find them in abundance on the twigs of rose-bushes. They have a peculiar swollen, quiescent look, and a brownish colour. No. 6 shows us another such fierce enemy at work. This formidable insect tiger is the larva of the wasp-fly ; he is a savage carnivore, v.ho moors himself by his tail end, stretches out to his full length, and swoops down upon his unsuspecting prey from above ; and being blessed with a good appetite, he can get rid of no fewer than 120 aphides in an hour. As he probably eats all day, with little intermission for rest and digestion, this gives a grand total of about 1500 or 1600 victims at a sitting. However, the remaining aphides go on budding away as fast as ever to make up the 14 Flasiii.ights on Nature dehciency, so the loss to the race is by no means irreparable. ** II ny a pas d'homme m^cessaire," Napoleon used to say ; and the principle is even more true as applied to the green-flies. If a few millions die, their place is soon filled again. Look once more at No. 6, and you will see that while the tiger-like enemy is engaged in hoisting and devouring one unfortunate aphis, its neighbour below, heedless of the tragedy, is quietly engaged in blowing off honey-dew. This blowing-off of honey-dew leads me on direct to the very heart of my subject ; for it is as manuf.icturers of honey- dew and as cows to the ants that aphides base their chief claim to at- tention. If they did not produce this Turkish delight of the insect world, nobody would have troubled to study them so closely. Let us go on to see, then, what is the origin and meaning of this curious and almost unique secretion. If you examine the leaves of a lime-tree or a rose-bush in warm summer weather you will find NO. 6. — TRACIC ENEMY WHO DEVOURS 120 PER HOUR. The Cows that Ants Milk IS means sai're," } even a few Dre at /ill see [er-like ;ecl in ouring aphis, below, •aj^edy, ^ed in y-dew. ■off of me on y heart r it is as honey- j to the ;s base I to at- did not Turkish d have [o on to of this ee or a ^ill find them covered all over witli a soft sticky substance, sweet to the taste, and spread in a thin layer upon the surface of the foliage. This sweet stuff is honey- dew, and it is manufactured solely by various kinds of aphides, without whose trade-mark none other is genuine. Why do they make it ? Not, you may be sure, out of pure unseltish moral desire to benefit the ants and other beasts that like it. In the animal world, nothing for nothing is the principle of con- duct. The true secret of the origin of honey-dew appears to be this. Aphides live entirely off a light diet of vegetable juices ; now, these juices are rich in compounds of hydrogen and carbon, especially sugar (or rather, to be strictly scientific, glucose), but are relatively deficient in nitrogenous materials, which last are needed as producers of movement by all animals, however sluggish. In order, therefore, to procure enough nitrogenous matter for its simple needs, your aphis is obliged to eat its way through a quite superfluous amount of sweets, or of sugar- forming substances. It is almost as though we ourselves had to swallow daily a barrel of treacle so as to reach at the bottom an ounce of beefsteak. To get rid of this surplus of sugar (or rather, un- digested glucose) almost all aphides (for they are a large family, with many separate kinds) have acquired a pair of peculiar organs, known as honey- tubes, on the backs of their bodies. Sometimes, when distended with superfluous food, they simply blow out the honey-dew secreted by these tubes on to the leaves below them. i6 Flashlights on Nature fi ^ti The aphis in No. 6 is represented at the moment when it is thus ridding itself of its excessive sweet- ness. But honey-dew is sticky, and apt to get in the way ; it may clog one's legs, or interfere with one's proboscis : so the aphides prefer as a rule to retain it prudently till some friendly animal, with a taste for sweets, steps in to relieve them of the unpleasant tension. The animal which especially performs this kind office for the rose -aphis is the NO. 7. — AN ANT MILKING A ROSE- APHIS OF ITS HONEY-DEW, garden ant ; and No. 7 represents such an ant in the very act of tapping and caressing an aphis with its feelers, in order to make her yield up on demand her store of honey. The process is ordinarily described as "milking." You must understand, of course, that neither aphis nor ant is actuated by purely philanthropic considerations ; this is a case of mutual accommo- The Cows that Ants Milk 17 dation. The aphis wants to ,»«W*,<« /jmf'' ' t^' m NO. 8. — COMIC ENEMY WHO POSES AS OLD-CLOTHES MAN. descendants of a single viviparous aphis would cover the earth with a ten feet thick layer of teeming green-flies. However, Nature has remedies in store for them. Storms of rain and hail kill myriads of aphides ; sudden changes of weather wilt them and nip them up ; innumerable enemies make an honest livelihood out of them. Another of these ubiqui- tous foes is graphically represented in No, 8 — the w 22 Flashlights on Nature i- * grub of the lace-wing fly, a sort of insect old-clothes man,