Diptera (Gr. twice, and wing), an order of insects, containing the fly, mosquito, etc, characterized by two wings, two knobbed threads (halteres, balancers or pois-ers) behind the wings, and a horny or fleshy proboscis. They undergo a complete transformation ; the larvae, usually called maggots,
Larva and Imago of the Bot Fly of the Ox (Hypodermia bovis).
have no feet, and have the breathing holes generally in the posterior part of the body; the pupae or nymphs are either incased in the dry skin of the larvae, or naked, showing the wings and legs free and unconfined. The head is large, globular, connected with the body by a very slender neck, and is capable of a considerable pivot-like motion; the greater part, especially in the males, is occupied by the brilliant compound eyes, the single ocelli, when they exist, being on the top of the head. Under the head is the proboscis or sucker, which in some kinds can be drawn up and concealed in the mouth; it consists of a long channel, ending in two fleshy lips, and enclosing on its upper side from two to six fine bristles, sharp as needles, and making the punctures so familiarly known in the case of mosquito bites; as this apparatus takes the place of the jaws of other insects, these wounds may properly be called bites. The saliva which flows into the wounds causes the well known swelling and itching. The sheath serves to maintain the lancets in position, and the latter having made their punctures form a groove along which the vegetable or animal fluids rise by the suctorial power of the insect and by capillary attraction.
In the flies which only lap their food the proboscis is large and fleshy. The antennae in the gnats are long and many-jointed, in the flies short and thick, at the base of the proboscis. The wings are generally horizontal and delicate, with many simple veins; the posterior wings are metamorphosed into the balancers or poisers. Some entomologists, as Latreille, think the poisers do not correspond to posterior wings, but are vesicular appendages connected with the posterior respiratory tracheae of the chest. Just behind the wing joints, and in front of the poisers, are two small convex scales, opening and shutting with the wings, and called winglets. The thorax is often the hardest part of the insect, composed principally of the mesothorax. The abdomen is not always united to the thorax by the whole of its posterior diameter, and in many females ends in a retractile jointed ovipositor. The legs, six in number, are usually long and slender, with five articulate tarsi and two claws at the end, besides two or three little cushion-like expansions, by means of which they are able to ascend the smoothest surfaces and to walk with the back downward with perfect security. According to Marcel de Serres, the dorsal vessel (the heart) in diptera is narrow and its pulsations are frequent.
Respiration in the adult is carried on by vesicular and tubular tracheae. The nervous system consists of an aggregate of cerebral ganglia, and in some of nine other ganglia, three in the thorax and six in the abdomen, connected by longitudinal simple commissures or cords; the larvae have usually one more pair of ganglia than the adults, and have the commissures often double. The proboscis being the transformed under lip, often geniculate, the perforating bristles may be regarded as maxillae, mandibles, and tongue. In those larvae which have a distinct head, as in the mosquito, the jaws are arranged for mastication, though some of the pieces are wanting; but in the acephalous maggots the mouth is suctorial. Communicating with the gullet is a thin-walled vesicle, the sucking stomach, in which the fluids swallowed are temporarily deposited; the stomach proper is long and narrow, and makes many convolutions in the abdomen. The end of the intestine is short, muscular, and pyriform. The uriniferous vessels are long, and generally four in number, opening into the lower extremity of the stomach; the ovaries consist usually of many short three- or four-chambered tubes, terminating in a short or a convoluted oviduct; the testicles are two, simple, and generally oval or pyriform, with long vasa deferentia ending in the ejaculatory duct in common with two simple accessory mucous glands, and with horny valves enveloping the projecting copu-latory organ.
The larvae or maggots are without legs, generally whitish, and vary exceedingly in form and habits. The larvae of the mosquito are aquatic, breathing with the head downward through the tubular tail surrounded with feather-like appendages, and the pupae tumble about in water by means of two oval fins. These larvae, and those of most flies which have four or six bristles in the proboscis, have a distinct horny head, and cast their skins to become pupae, which are generally brownish; many have thorns and prickles on the body by which they work their way out of their coverings; a few cover themselves with silken webs and spin cocoons. The larvae of other flies, with a soft retractile head, living by suction, increase rapidly in size, and change their form without casting off their skins, which shorten and harden, forming a case within which the larva changes into a pupa, which comes forth a fly by forcing oft* one end of the case. Though this order contains the bloodthirsty mosquito, the disgusting flesh fly, and many insects depositing their eggs in the bodies of living animals, it is most useful, supplying food to insectivorous birds, and consuming decomposing animal and vegetable substances.
Their life in the perfect state is short, very few surviving the rigor of winter. - Among the genera with many-jointed antennae the following are the most interesting and best known: Culex (Linn.) contains the well known gnats and mosquitoes, whose larvae and pupae are so common in stagnant water, called wigglers and tumblers, and whose adult females pierce with their lancets and annoy by their nocturnal hum the human race from Lapland to the tropics; the best known species are the C. pipiens of Europe, and the G. Americanus of this country, which is probably distinct. The genus cecidomyia (Latr.) includes many species interesting to the agriculturist, as the Hessian fly (C. destructor, Say), the wheat fly (C. tritici, Kirby), and the willow-gall fly (C. salicis, Fitch), injurious in the larva state. The genus tipula (Linn.), especially T. oleracea (Linn.), commonly known in England by the name of Harry Long-legs, is noted for its depredations in the larva condition on the tender roots of meadow plants.
In the genus simulium (Latr.) are the black fly and the midges of the northern parts of America. The black fly (S. molestum, Harris) fills the air during the month of June in Canada and the northern states; it flies in the daytime, and is so savage that every bite draws blood, sometimes accompanied by considerable irritation; it is black, with transparent wings, and about 1/10 of an inch long. After continuing through June, it is followed by another species (S. no-civun, Harris), called "no-see-'em" by the Indians of Maine from their minuteness; they come forth toward evening, creep under any kind of garment, and produce a sharp, fiery pain without drawing blood; they are very troublesome in July and August. Among those with few joints in the antennae is the genus tabanus (Linn.) which contains the large horse flies, as T. bovinus (Linn.), dark brown, an inch long, common in Europe, where there are more than 40 other species. The most common American species is T. atratus (Fabr.), black with a whitish bloom on the back; the eyes are very large, shining black, with two jet-black bands across them; it is about an inch long, with an expanse of wings of two inches. The orange-belted horse fly (T. cinctus, Fabr.) is smaller and less common, black, with the first three rings of the body orange.
A smaller species is T. lineola (Fabr.), with a whitish line along the top of the hind body. In summer these flies are very troublesome to cattle and horses, being able to pierce through the thickest hide with their six-armed proboscis; a strong decoction of walnut leaves, applied as a wash, is said to keep them off. The golden-eyed forest flies (chrysops, Meig.) are known by their brilliant spotted eyes and their banded wings; smaller than horse flies, they resemble them in their habits, frequenting woods and thickets in July and August; some are wholly black, others striped with black and yellow. The bee fly (bombylius cequalis, Fabr.) flies with great swiftness through sunny paths in the woods, hovering over flowers and sucking their honey, like humming birds; it is about three eighths of an inch long, shaped like a humble-bee, and covered with yellowish hairs; the ex-panse of the wings is about an inch; they are divided longitudinally into two equal parts by the colors, the outer half being dark brown and the inner colorless.
Among the flies which prey on other insects, seizing them on the wing or on plants, is the genus midas (Latr.), of which the orange-banded species (M. filatus, Fabr.) is sometimes 1 1/4 in. long and 2 1/4 in. in expanse of wings; the general color is black; it frequents the woods in July and August, where it may be often seen flying or basking in the sun; the larva is a cylindrical maggot, growing to the length of 2 in.; the pupa measures 1 1/4 in. in length, is brown, with forked tail, eight thorns on the fore part of the body, and numerous sharp teeth on the edges of the abdominal rings; it pushes itself half out of its hole when the fly is about to come forth. The genera laphria (Fabr.) and asilus (Linn.) are also predaceous in the winged state; in the former the antennae are blunt at the end. in the latter slender-pointed; the former resemble large bumblebees in their thick and heavy bodies and legs. In the larva state these asil-ians live in the ground, where they do much mischief to the roots of plants.
The soldier flies (stratiomydoe) have two spines on the hinder part of the thorax; the proboscis contains only four bristles, and ends with fleshy lips adapted for sucking vegetable juices; they are fond of wet places, and their larvae live in stagnant pools, some thrusting their breathing tube out of the water; they undergo transformation within the hardened larval skin. The genus stratiomys (Geoff.) has a broad oval body, of a dark color, with yellow markings on each side, and the antennae somewhat spindle-shaped. The genus sargus (Fabr.) is said to have no spines on the thorax, a slender body, of a brilliant grass-green, about half an inch long, with a bristle on the end of the antennae. These insects delight in sunny weather, being dull and inactive in cloudy days; the larvae are found in dung and rich mould. The syrphidoe have also a fleshy proboscis, and live on the honey of flowers; they resemble bees, wasps, and hornets in shape and color, and sometimes lay their eggs in the nests of these insects; others drop their ova among plant lice, which the young eagerly feed upon.
The larvae of the genus helophilus (Meig.) were named by Reaumur rat-tailed maggots, from the great length of their tubular tails, which serve as respiratory organs; the experiments of Reaumur show that while the insect lies concealed in mud, its respiratory tube may reach five inches to the surface of the water; it seems to be composed of two portions, which slide one into the other like the joints of a telescope. Some of the larvae of this family live in rotten wood. The family conopidoe resemble slender-bodied wasps; the antennae are long and three-jointed; the proboscis is long, slender, and geniculate. The genus conops (Linn.) is generally black, and about half an inch long; more than 20 species are described, usually found on flowers in June and July, but not in large numbers; they deposit their eggs in the larvae and the perfect insects of the bumblebee, in whose bodies their young undergo metamorphosis. The common stable fly belongs to the genus stomoxys (Fabr.); the flesh fly to sarcophaga (Meig.); the house fly and the meat fly to musca (Linn.); the flower flies to anthomyia (Meig.); the cheese fly to piophila (Fallen.); the dung fly to scatophaga (Meig.); the fruit and gall flies to ortalis (Fallen.) and tephritis (Latr.). (See Fly.) The gadflies or bot flies, comprising the genera oestrus (Linn.) and gas-terophilus (Leach), affect respectively the ox and the horse. (See Gadfly.) Various winged and wingless ticks infest the horse, sheep, and birds, belonging to the order of diptera, but forming with the spider flies the order homa-loptera of Leach and the English entomologists; they include the genera hippobosca (Linn.), melophagus (Latr.), and ornithomyia (Latr.). (See Tick.) The pulicidoe, or fleas, are wingless diptera, with hard, compressed bodies, a sucker-like mouth, and hind legs formed for leaping; they live principally upon the bodies of other animals. (See Epizoa.) - At the end of this order may be mentioned the genus nycte-ribia (Latr.), the spider fly, a wingless insect resembling a spider; the small head seems a mere tubercle on the anterior and dorsal portion of the thorax; the eyes are like minute grains; the thorax is semicircular; the antennae are extremely short, inserted close together, and immediately in front of the eyes.
These flies nestle in the hair of bats, among which they move with great rapidity; according to Col. Montagu, when they suck the blood of bats they are obliged to place themselves on their backs on account of the dorsal position of the head. This last division of the diptera is not produced from eggs deposited in the usual manner, but the larva is hatched and developed within the body of the mother, and is not born till it arrives at the state of pupa; hence these genera have been called pupipara by Latreille. The pupa when born is nearly as large as the parent, enclosed in a cocoon, the altered skin of the larva at first soft and white, but soon growing hard and brown; it is notched at one end, where the mature insect escapes. The genera of diptera make up for their small size by their countless swarms.