Diptera

“ Osten Sacken states that among Diptera the aerial forms (Bombylidæ, etc.) with their large eyes or holoptic heads, which carry with them the power of hovering or poising, have weak legs, principally fit for alighting. On the other hand, the pedestrian or walking Diptera (Asilidæ, etc.) “use the legs not for alighting only, but for running, and all kinds of other work, seizing their prey, carrying 99it, climbing, digging, etc.; their legs are provided not only with spines and bristles, but with still other appendages, which may be useful, or only ornamental, as secondary sexual characters.” ”

“ No exploration of the gallery—no anxiety for the distressed larva; though the grub, whose delicate skin has just exchanged the gentle moisture of a cave for burning sunshine, is writhing on its heap of chewed Diptera, the mother takes no notice of it. For her it is no more than any one of the objects strewn on the sand,—a little pebble, a clod, a scrap of dried mud,—nothing more. It is undeserving of attention. This tender, faithful mother, who wears herself out in efforts to reach her nursling’s cradle, cares nothing just now but for her entrance door—the door she is used to. ”

“ Diptera as an order are probably more widely distributed over the earth’s surface than are the representatives of any similar division of the animal kingdom. Flies seem capable of adapting themselves to extremes of cold equally as well as to those of heat, and species belonging to the order are almost invariably included in the collections brought back by members of Arctic expeditions. ”

“ F. Brauer (1863) divided the Diptera into two sub-orders [8] ; of the first of these a Crane-fly or 'Daddy-long-legs' may be taken as typical, of the second an ordinary House-fly or Bluebottle. All the larvae of the Diptera are legless, those of the Crane-fly group have well-developed hard heads, with biting mandibles, but in the House-fly section the larva is of the degraded vermiculiform type known as the maggot, not only legless, but without a definite head, the front end of the creature usually tapering to the mouth, where there are a pair of strong hooks, used for tearing up the food. ”

“ To neither category belong the beetles, whose wing-covers are peculiar organs of flight, and not for direct use, and the Diptera, which possess but a single pair of wings. In the beetles the hind wings, in the Diptera the fore wings, serve especially as organs of flight. It may be observed that the Diptera are the best fliers, and that those insects which use both pairs of wings as a single pair fly better than those insects whose two pairs of wings work independently of each other. ”

“ It may confidently be asserted that, of insects which directly or indirectly affect the welfare of man, Diptera form the vast majority, and it is a moot point whether the good effected by many species in the rapid clearing away of animal and vegetable impurities, and in keeping other insect enemies in check, counterbalances the evil and annoyance wrought by a large section of the Order. ”

“ The stages of metamorphosis in the Diptera are no more suddenly acquired than in the bee or butterfly. In all these insects the rudiments of the wings, legs, and even of the ovipositor of the adult exist in the young larva. ”

“ A true food-reservoir is present in most Diptera (Fig. 308) as well as in the larvæ of the Muscidæ, but according to Dufour it is wanting in some Asilidæ and in Diptera pupipara, and according to Brauer in the Œstridæ. The food-reservoir in Diptera is always situated on the left side of the digestive canal; there is usually a long neck or canal, while the reservoir is either oval or more usually bilobed, and often each lobe is itself curiously lobed.
In Lepidoptera (Figs. 309, 310) the so-called “sucking stomach” is, as Graber has proved, simply a reservoir for the temporary reception of food ”

“ Diptera are divided into some sixty families, the exact classification of which has not yet been finally settled. The majority of authors, however, follow Brauer in dividing the order into two sections, Orthorrhapha and Cyclorrhapha, according to the manner in which the pupa-case splits to admit of the escape of the perfect insect. ”

“ With the exception of a few species from the Solenhofen lithographic Oolite, fossil Diptera belong to the Tertiary Period, during which the members of this order attained a high degree of development. In amber, as proved by the deposits on the shores of the Baltic, the proverbial “fly” is more numerous than any other creatures, and with very few exceptions representatives of all the existing families have been found. ”

“ Why does the spoiler kill the prey instead of paralysing it? Is it want of skill with the sting? Is it a difficulty arising from the organisation of the Diptera or from the manœuvres of the chase? I must own, at once, that I have failed to put a Dipteron, without killing it, into that state of complete immobility into which it is so easy to plunge a Buprestis, a Weevil, or a Scarabæus, by injecting a little drop of ammonia, on the point of a needle, into the thoracic ganglia. It is difficult to render your subject motionless ”

“ All these Diptera, great and small, placed in paper twists where air circulates, dry up and grow brittle in two or three days, [235] while all kept from evaporation in glass tubes, where the air is stagnant, grow mouldy and decay. So they are dead—really dead—when carried to the larva. If some few preserve a little life, a few days, a few hours ends all. Not being clever enough to use its sting, or for some other reason, the assassin kills its victims outright.
Knowing this complete death of the prey at the moment when it is seized, who would not admire the logic of the Bembecid’s manœuvres? ”

“ I shall be very glad of the opportunity of examining the Hymenopterous Parasites of Diptera. I begin to think that Lucca will yield me more among these my oldfavourites, than of Diptera. I believe my last letter to you was written too far back, for me to have mentioned the capture of a species of Iteaphila (a Northern genus, I think, it was considered,) at no great elevation. I was driving, with a friend in one of the country vehicles, home from the Baths, out in the wildest, rocky, part of the valley of the Serchio, I was attracted by the conspicuous white flowers of a Cerastium. ”

“ This opinion, however, is manifestly erroneous; the pupæ of the nemocerous Diptera are on precisely the same footing as those of the Lepidoptera, and it would be almost as reasonable to call one of these active, because it wriggles out of its cocoon in the earth before the emergence of the moth. The perfect mosquito emerges from a rent in the thoracic shield of the pupa, drawing each pair of legs out separately, and placing them in front of it on the water; the wings and abdomen are then extracted and in a few moments it flies away. ”

“ They might be thought to be adapted for fighting, but as in one species they are of a beautiful pink colour, edged with black, with a pale central stripe, and as these insects have altogether a very elegant appearance, it is perhaps more probable that they serve as ornaments. That the males of some Diptera fight together is certain ”

“ Passing over several orders of insects which do not seem to have any marine representatives, we come to the Diptera or two-winged insects, of which the familiar house-fly is a type, and here we have to deal with those troublesome creatures that literally swarm in the neighbourhood of the matter washed up to the highest level of the tide during the whole of the summer months. But although these insects are so very numerous, we do not find among them a particularly large number of species, their abundance being due more to the extreme prolificacy of those that occur. ”

“ I well remember to have seen a figure of Dicera and to have been stuck with its singularity, but I did not recognise it among Darwins insects of these U have a few more Diptera etc. for you which I had set before I received your letter. Darwin still has multitudes of them, and if I can procure them from Waterhouse before I leave I will bring them in pill boxes as you advise ............ Almost all I have seen of Darwins Diptera are as minute as those that you have. Chalcidites are also generally remarkable for their identity with the British forms. ”

“ Compared with the beetles, Diptera or flies take a very prominent position as promoters of cross-fertilization. One great advantage which they have over the former class is their power of free and rapid motion. While the beetles are almost without exception compelled to adopt a slow mode of locomotion, the movements of the flies are among the most rapid known in the insect world. The number of native species of Diptera is very large ”

“ That Diptera of the type of the common house-fly are often in large measure responsible for the spread of such diseases as cholera and enteric fever is undeniable, and as regards blood-sucking forms, in addition to those to which reference has already been made, it is sufficient to mention the vast army of pests constituted by the midges, sand-flies, horse-flies, &c., from the attacks of which domestic animals suffer equally with man, in addition to being frequently infested with the larvae of the bot and warble flies (Gastrophilus, Oestrus and Hypoderma) . ”

“ The wings, which are variously veined, though appearing naked to the unaided eye, are often thickly covered with very minute hairs or hooks. As an order the Diptera are decidedly injurious to man, whether we consider the annoyances to ourselves or our animals of the Mosquito, Buffalo-gnat, Gad-fly, Breeze-fly, Zimb or Stomoxys, or the injury to our crops of the Hessian-fly, Wheat-midge, Cabbage-maggot, Onion-maggot, etc. ”

“ The order of the Diptera is a large one, and we might go on indefinitely describing interesting things about flies m general. Such a course, however, would soon fill a larger book than this; hence, since we are already in the last chapter, a more practical plan will be to select for special consideration a few species that have become closely as- sociated with the welfare of man or of his domesticated animais. Such species include the mosquitoes, the bouse fly, the blowfly, the stable fly, the tsetse fly, the flesh files, and related forms. ”

“ The meat-fly.—Ed.
[9] It is probable that one day the order Aptera will be superseded. The absence of wings is not really a character of great value. De Blainville, Mollard, Pouchet, Van Beneden, and Gervais, have made several attempts in that direction. The fleas have been placed among the Diptera, and the lice among Hemiptera in the "Traité de Zoologie Médicale" of these two last authors. ”

“ But, returning from this digression, we find in the Diptera the habit of obtrusion and intrusion, of coming in actual contact with our food and our persons, combined with another propensity--that of feeding upon carrion, excrement, blood, pus, and morbid matter of all kinds. This is a combination far more serious than is generally imagined. If the fly--which may at any moment settle upon our lips, our eyes, or upon an abraded part of our skin--were cleanly in its habits, we need feel little annoyance at its visits. ”

“ These Diptera, which are worthy of so much attention, and deserve so much study with regard to the part they play in the general economy of Nature, are an object of fear and repulsion when one considers their relations to us and other animals. ”

“ The house-fly and the bluebottle fly also belong to the order of the Diptera. They are not very pleasant insects, but while they are grubs they are really most useful, for they feed upon [386] all sorts of decaying substances. And another insect, called the flesh-fly, is even more useful still, for it is the parent of from sixteen to twenty thousand grubs: so that if even a single fly finds the carcass of a small animal and leaves her eggs upon it, the little ones that soon hatch out will devour it in a very short time. ”

“ Fig. 346.—Portion of a urinary tube of Calliphora vomitoria: tr, trachea; l, lumen; k, nucleus.—After Gegenbaur.
While usually the urinary vessels form simple tubes, in many species of Lepidoptera and Diptera they are branched, thus resembling those of spiders and scorpions. Moreover, in many Lepidoptera and Diptera (Fig. 308) , the tubes are not simple, but are lobulated, and in some Hemiptera (Pentatoma, Notonecta, and Tettigonia) are twisted or lace-like. In rare cases there are two kinds of urinary tubes ”

“ Amongst the numerous families into which the true flies (Diptera) are divided, none are more harmful to human enterprise than that of the Oestridae, or bot-flies, inasmuch as every single species and every single member of this family passes its larval stage within the tissues of some vertebrate host, and frequently in those of domesticated cattle; sometimes even in man himself. ”

“ The antennae of Diptera, which are also extremely important in classification, are thread-like in the more primitive families, such as the Tipulidae (daddy-long-legs) , where they consist of a considerable number of joints, all of which except the first two, and sometimes also the last two, are similar in shape; in the more specialized families, such as the Tabanidae (horse-flies) , Syrphidae (hover-flies) or Muscidae (house-flies, blue-bottles and their allies) , the number of antennal joints is greatly reduced by coalescence, so that the antennae appear to consist of only three joints. ”

“ In pit-like depressions of the antennæ arise nerve-rods (without a chitinous case) which stand in direct relation with a ganglion-cell lying under it. These pits are either simple, viz. with only an ‘olfactory rod’ (Tabanus, Fig. 283, and other Diptera, Vanessa) , or compound (Muscidæ, and most other Diptera, and Philonthus) . It is important that these pits are partly open (in the above-named groups of insects) , and partly closed and covered with a thin membrane, under whose concavity the olfactory rods end (Orthoptera, Melolontha, and other lamellicorns) . 3. ”