Part 21

The =Common Flies= (Musca)

are coloured dark or shining green. The headless white maggots live in dung (=House Fly= = Musca domestica), in fresh or decaying meat (=Blue-bottle= = M. vomitoria), exceptionally (M. vomitoria) in wounds that are not kept clean, or in the vagina of several domestic animals. Remedy: Compare above (“Flesh Fly”).

The =Flower Flies= (Anthomyia).

These are found on flowers, and resemble many common flies in appearance and colour. The headless white maggots live in dung, also in decaying or sound parts of plants; a few species may sometimes develop in the one kind of material, sometimes in the other. Anthomyia meteorica swarms round the heads of domestic animals, and may even cause inflammation of the eyes and ears. The =Wheat Bulb Fly= (Anthomyia coarctata, about a quarter of an inch long, yellowish grey, with black hairs) lives as a larva during winter and spring in the hearts of rye and wheat plants, the leaves of which become yellow in consequence. During April and the beginning of May the larvæ quit these plants and become pupæ in the ground. The second generation can, in like manner, live in various kinds of summer grain. The =Lupine Fly= (A. funesta)—nearly one-fifth of an inch long, brownish grey (male) or whitish grey (female), with black legs—digs, when a larva, tunnels in the roots, stems, and seed-leaves of young lupine plants, causing the root and stem to turn black, and the seed-leaves to wither. Preventive Measure: Early sowing of the lupines. The =Mangold and Beet Fly= (A. betæ), a quarter of an inch long, yellowish grey, lays its eggs, five to eight in number, in the young leaves of mangold and beet. The maggots devour the green substance of the leaf between the two layers of epidermis, so that the leaves die. In June the maggots creep out of the leaves, and become pupæ in the soil. The flies quickly escape, and two or three generations follow one another in the year. As, however, the leaves are now larger, the later generations only effect a small amount of damage. Preventive Measure: Close sowing of the turnips, so that even if many are killed there will still be enough young plants. The =Cabbage Root-eating Fly= (A. radicum) and the =Radish Fly= (A. floralis) live as fleshy, wrinkled, dirty white maggots with black dots, in the underground parts of turnip, cabbage, horseradish, radishes, etc. They lead a similar life to the =Cabbage Fly= (A. brassicæ), the cylindrical, smooth, yellowish white maggot of which lives in the underground parts of cabbage, turnip, and rape. The roots attacked swell here and there (Fig. 116), and later on decay; the leaves of the infested plants first become of a dull leaden colour and then wither. Entire fields of cabbage, rape, or turnips, are often destroyed by cabbage fly maggots. The insect passes the winter in the pupa state; the flies appear early in the spring, and usually twice more later on. It is therefore most desirable to pull up and burn the infested plants as soon as possible. A proper rotation of crops should also be practised. [The =Onion Fly= (A. ceparum) maggot feeds within the bulbs of stored onions. The male fly is grey, the female yellow.]

FIG. 116.—A turnip infested by the Cabbage Fly: A, swellings; G, tunnels. ]

The =Cheese Fly= (Piophila casei),

one-fifth of an inch long, slender, with a metallic sheen, almost hairless, black, with dirty yellow legs and wings of glassy clearness. These small flies abound in front of the windows of places where cheese is stored; in summer and autumn the shining white maggots, which are cylindrical in form with tapering ends, and one-third of an inch long, live in large numbers in old cheese, gnawing it through and through, and making it dirty. Now and then they spring forwards by bending their bodies into a circle and suddenly straightening them again. They become pupæ on the walls or in straw, near the cheeses from which they have crept out. Remedies: Keeping the cheeses clean; mechanical exclusion (gauze screens outside the windows, enclosure in chests).

The =Green-eyed Flies= (Chlorops)

include a number of small flies, under one-sixth of an inch long, with spherical head, rounded greenish eyes, strongly arched thorax, and short egg-shaped abdomen, pointed in the male and blunt in the female. The headless larvæ live in the haulms of grasses and species of grain; the life history of a few forms only is adequately known. A few are harmful, especially as there are two or three generations annually. The late summer generation often appears in large numbers, indeed in actual swarms. Since no species lives exclusively on corn, it is impossible to keep them down for a long period of time. I describe only two species:—

FIG. 117.—The Ribbon-footed Corn Fly (Chlorops tæniopus). ]

The =Ribbon-footed Corn Fly= or =Yellow Haulm Fly= (Chlorops tæniopus), nearly one-sixth of an inch long, shining yellow; the antennæ are black, and there are three longitudinal stripes on the dorsal side of the thorax and four transverse bands on the abdomen of the same colour; the latter region is scarcely longer than the thorax. The insect (Fig. 117) is on the wing in cornfields about the middle of May. It lays its eggs separately on the upper leaves of various species of wheat, rye, and barley, choosing the upper side of the blade, not far from the sheath. Only those plants are selected for the purpose in which the ears are still hidden deep down between the leaf-sheaths. Wheat plants are picked out whenever possible. The maggot when hatched works its way between leaf-sheath and haulm, digging into the latter. It is yellowish white, clear and translucent, and about a quarter of an inch long. While still young it penetrates the haulm, and then attacks the developing ear or the upper part of the haulm which immediately adjoins this, and travels gradually up to the first node of the haulm or nearly so, always continuing to slowly suck. Thus a furrow, from 2½ to 3½ inches long (Fig. 118, C and D), is formed along the surface of the upper part of the haulm, and often also along the lower part of the ear. The part of the haulm attacked swells transversely, and the part below often remains short, so that the ear cannot emerge from the leaf-sheath; but, in any case, only small worthless grains are developed. The furrow is always much deeper below than above, and its margins thicken in consequence of the swelling of the tissues of the haulm. At the end of June or in July, the larva becomes a pupa at the lower end of the furrow. The yellowish-brown pupa (Fig. 118, B), one-fifth of an inch long, remains as such in the furrow for three weeks; the fly emerges in August. Very considerable damage may be done by the first generation, of which the habits have just been described. During 1869 in Silesia, from two-thirds to five-sixths of the ears in many fields remained hidden in the leaf-sheaths, and consequently gave no increase. The first generation of the ribbon-footed corn fly can also develop in the way described in the haulms of several grasses, e.g. in species of Poa and Holcus.

The flies, emerging in late summer, lay their eggs, here, too, separately, on the leaves of grass or corn. Wherever possible, they seek out for the purpose the winter wheat plants then present in the fields, but also content themselves with rye, or even with wild or meadow grasses; they have to be satisfied with grasses if, at the time of egg-laying, the winter corn is not yet up. The maggot, when hatched, works its way to the inner side of the leaf-sheath, and thence to the apex of the still very small haulm; there it remains during the winter. The damage becomes apparent the following spring. The growth in length of the haulm in question is extremely small, while growth in thickness increases to an abnormal extent. Almost all the leaves completely surround the haulm, which swells to an enormous extent (Fig. 119), together with the enclosing leaf-sheaths, which are much broader than usual. The unattacked plants are naturally much larger than the sickly ones, and deprive these of air and light, so that they die down, being overshadowed, not only by the sound haulms, but also by their own secondary shoots. The resulting damage may be tolerably great, especially at the edges of the field. It may happen that both summer and winter generations of the ribbon-footed corn fly are harmful in the same district; but it frequently happens that only one or the other is complained of in a particular spot. It is only natural that the flies, which swarm around in May, and again in August, September, or October, should not always find suitable corn plants upon which to deposit their eggs. In such cases grasses are used. Remedies: Sowing the summer corn as early as possible, that it may be developed to a stage which is unsuitable for the purpose of egg-laying, before the flies appear. The winter seed, however, must be sown as late as possible, so that the second generation of flies may find no corn plants fit to lay their eggs upon. Bearded wheat, especially the strongest varieties, should be sown in preference to awnless wheat. Careful tillage and suitable manuring, so that strong plants of rapid growth may be produced.

FIG. 118.—The Ribbon-footed Corn Fly (Chlorops tæniopus); larva (A) and pupa (B) magnified. To the left a wheat haulm and ear (C) with the furrow (q) dug out by the larva; the pupa (p) is seen at the bottom of the furrow. To the right a wheat haulm with furrow (D) and the larva (r) lying in it. ]

FIG. 119.—A wheat plant distorted by the winter generation of the Ribbon-footed Corn Fly. ]

The =Frit Fly= (Chlorops, or Oscinis frit)

(Fig. 120, C) is about one-tenth of an inch long, shining black, with a metallic sheen. Legs short, feet yellow. Maggot (Fig. 120, A) yellowish white, about one-eighth of an inch long, cylindrical, and tapering in front. Usually three generations. 1. The maggots of the first generation are found during May, in the lower part of the haulm of summer corn (especially oats and barley); the plants attacked either die off entirely, or some haulms develop further, remaining small, however, and yielding only a few light grains. The base of the haulm thickens abnormally, but the growth in length is always small; the leaves, too, grow badly, first becoming yellowish at the tip, and then entirely yellow or reddish. The symptoms of disease are exhibited to a less or greater extent, according as few or many (even up to ten) maggots inhabit the base of a plant. The shining brown pupæ (Fig. 120, B) are found in the lower part of the haulm, or between the leaf-sheath and the haulm (Fig. 120, D). The adult insect is on the wing at the end of May and in June. The first generation often appear on wild or meadow grasses, and are chiefly seen on summer corn when this is sown late or develops slowly. 2. The maggots of the second generation are found in average cases during July, on the as yet scarcely ripe grains of late summer corn, principally those of oats and barley, often occurring also in the haulms of grasses. They keep between the awns, and suck the juices of the soft developing grains, which are rendered incapable of growth, and in any case remain light. The maggots of the second generation develop more quickly than those of the first or third; they are mature in three weeks. The pupa rest is very short, and the flies appear in August, September, or October. They lay their eggs on the leaves of winter corn or winter grasses, and from these eggs are developed (3) the maggots of the third generation, which are to be found, during September and October, in the heart of winter corn and grasses, injuring these plants in exactly the same way that the maggots of the first generation injure the summer corn. The insect passes the winter as a pupa in winter corn plants or grasses. It is but very rarely that all three generations infest the corn of any particular region; as a rule, only the first, second, or third generations do this, or the first and third; in such cases the other generations live on grasses. Remedies: Extermination of the insect is impossible, since it can always go from corn to grass plants. Oats and barley are almost always attacked in spring, if in the immediate neighbourhood there is winter rye inhabited by the maggots, for the flies, when they emerge the next spring, seek out the summer corn. This may, however, be made impossible, or at least difficult, if a field of peas, clover, lupines, rape, or some other crop not of gramineous nature, is interposed between fields of winter corn and those of oats, barley, or similar late sown crops of summer corn. Sowing the summer corn (especially oats and barley) as early as possible.

FIG. 120.—The Frit Fly (Oscinis frit, L.): A, larva; B, pupa; C, fly; D, a diseased corn plant, as appearing in spring,—the larvæ and pupæ are seen of the natural size in the lower part of the plant. ]

Family: =Syrphidæ= (Hover or Hawk Flies).

Chiefly includes brightly coloured flies, marked with yellow or red and black bands or patches (Fig. 67), and flying rapidly with a buzzing noise. They can remain suspended at the same point in the air by moving their wings up and down with great rapidity. A few of them resemble the humblebee in their thick covering of hair; others, with yellow and black abdomen, look like wasps (Syrphus). The proboscis is adapted for sucking, but not for piercing; these flies suck their food from flowers. They are fond of hovering in the air in sunny places. The legless larvæ vary, according to species, in their habits, and consequently in their structure. Some (those of the =Drone Flies=, Eristalis) live in stagnant water; others (e.g. those of Eumerus lunulatus) live in onions, which they hollow out; while some, again, develop in rotten wood, etc. The maggots of the =Aphis-eating Flies= (Syrphus), however, feed on insects, chiefly aphides, which they suck out completely. They are elongated, tapering in front, thickened behind, move like leeches, and vary much in colour (green, yellow, brown, chequered), according to the species. As they grow quickly, and consequently more than one generation is found each year, and as they are very voracious, we must look upon them as powerful allies for the extermination of aphides.

Family: =Stomoxydæ= (Stable Flies).

In many points the stable flies resemble ordinary flies, but their mouths are adapted for piercing. Their painful bites make them known to every one as pests to human beings and cattle. Here belongs the common =Stable Fly= (Stomoxys calcitrans), a form often confounded with the house fly, but distinguished from it by a sharp proboscis projecting at right angles, besides which the abdomen is more of a yellowish grey. The maggots usually live in dung. Two generations yearly: the first flies about in March; the second, and much more numerous one, in August and September. Remedies: Cp. p. 165.

Family: =Œstridæ= (Bot Flies).

Medium-sized or large flies (Fig. 121), with thick hemispherical heads, and mouth-parts not strongly developed. The antennæ can be drawn back into deep pits. The hot flies make a buzzing sound during flight. The headless, twelve-ringed maggots live in the bodies of various mammals. Their skin is provided with numerous wart-like projections, or circlets of spines. When very young the maggots are elongated and cylindrical, and then possess a mouth-hook, which disappears during the later moults. As soon as the maggots are fully developed they leave the body of the animal they inhabit, and let themselves fall to the ground, where they become pupæ within the shrivelled larval skin.

The following genera are distinguished: =Warble Flies= (Hypoderma), and =Bot Flies= (Œstrus and Gastrus, or Gastrophilus). To the first-named genus belongs the

=Ox Warble-fly=, or =Ox Bot Fly= (Hypoderma bovis),

two-fifths of an inch long, black. Hair: whitish yellow on the head; reddish yellow on the fore part of the thorax, black on the hinder part; grey on the fore part of the abdomen, black in the middle, and reddish yellow behind. Legs black. Wings brownish, not quite transparent.

On the wing during summer (June to September). As soon as the cattle hear the flies buzzing around (especially on hot days) they become very restless, run about as if mad, and even plunge down steep places. Young cattle are selected for egg-laying; the elongated white eggs are fixed separately to hairs. The maggot, elongated when first hatched, perforates the skin, and gets into the subcutaneous connective tissue, where it does not, as a rule, keep to any one place, but wanders here and there, sometimes penetrating the flesh, or even entering the spinal canal. It always, however, wanders back again later on into the subcutaneous connective tissue, where it gives rise, during the winter or the following spring, to one of the well-known tumours, or “warbles.” After fixing on a definite spot, it moults, becoming broader, and of a yellowish white colour. The maggot first causes an increased flow of blood to the part, and then inflammation. An excavation filled with matter is thus developed, and there is gradually formed a connective tissue sac communicating with the exterior by a minute tube. In spring, or early summer, the warble, which is visible externally, has reached the size of a pigeon’s egg; the maggot meanwhile becomes first greyish yellow, then brown patches appear, and lastly it assumes a dark brown colour, is an inch long or rather more, and somewhat swollen. It is now ready to pass into the resting stage, crawls out, and lets itself fall to the ground, where, within the larval skin, it becomes a black pupa four-fifths of an inch long, from which, about four weeks later, the fly creeps out. Damage done: If the warbles occur only in small numbers on an animal, its health is not much affected, though this must undoubtedly be the case if there are many, say fifty, or even up to a hundred, in the same animal. In such cases the yield of milk will be considerably diminished. Holes, too, are present in the skin, which, though they may close again, if the animal remains alive, always leave a thin place. The outer surface of meat from animals infested with warbles is dirty yellow, flaccid, or even soft and jelly-like (“licked beef”); it must be scraped off. Enemies: Starlings settle, in spring, on the backs of infested cattle, and seize the parasites with their beaks. Starlings, rooks, and wagtails destroy the maggots ready to become pupæ, as they lie on the ground. Remedies: Washing the back, shoulders, and loins with vinegar extract of walnut leaves during the summer, to keep away the bot flies. In spring: squeezing out the maggots from the warbles, having previously opened them, when necessary, with a penknife. If the warble is “ripe,” i.e. if it has opened so far that the black hinder end of the maggot can be seen, the opening may be stopped with fat or cart-grease, by which the larva will be killed where it lies.

The =Sheep Bot Fly= (Œstrus ovis),