FLIES
PART II
THE BLUE-BOTTLE (Calliphora erythrocephala), AND OTHERS
Who fills our butchers’ shops with large blue flies?
(Rejected Addresses.)
BUT there are other flies: first amongst which may be mentioned Fannia canicularis and F. scalaris. These belong to the family known as Anthomyidae, and are distinguished from the house-fly by being smaller in size, and by many other small details in the imago stage hardly to be appreciated except by trained dipterologists. For a short time at the beginning of the summer, during part of May and June, specimens of F. canicularis are more abundant than M. domestica, and, when seen on the window-panes of our living-rooms, are apt to be thought, by the uninformed, to be young specimens of the latter. But, as has been said, flies, when they are once flies, do not grow; all the growing they do is done in the larval stage.
FIG. 23.—Latrine-fly, Fannia scalaris, male (× 3). Antenna. Head of female, dorsal view. Natural size, resting position. (From Graham-Smith.)
As the days lengthen the common house-fly becomes vastly more common than F. canicularis, the ‘lesser house-fly,’ and the latter now tend to aggregate in those rooms of our houses not devoted to cooking, and may frequently be noticed flying in a jerky and disconcerting manner around the chandeliers or bedposts in unfrequented living- or bed-rooms. The relative proportion of these two genera in full summer varies in different localities. Roughly speaking, out of 100 flies collected in a house there is something between 90 and 99 per cent. of M. domestica, but the numbers not only vary with locality, but with temperature.
On the other hand, there is a curious disproportion between the number of sexes found ‘at home’ in the lesser house-fly. For every 100 F. canicularis taken indoors seventy to seventy-five are males, the numbers being evened by an equal preponderance of females who have remained out of doors.
FIG. 24.—Larva of F. canicularis. (From Gordon Hewitt’s Report to Local Government Board, 1912.) Magnified.
The larva of Fannia is a flattened-looking grub with distinct segments, decorated by numerous feathery processes. It lives amongst decaying vegetation and fruit, and also amongst fermenting animal matter and dejecta. Sometimes it is found in rotting grass. As we shall see later, it frequently passes into the human alimentary canal. F. scalaris, usually known as the ‘latrine-fly,’ is even commoner than its congener, and the external structural differences are minute. As its name indicates, it is found as a rule breeding in human dejecta, and is, therefore, as a typhoid carrier, much more dangerous than F. canicularis. Its larva is also more commonly found in the human intestine.
Then there are two species of large flies known as blue-bottles or blow-flies—Calliphora erythrocephala and C. vomitoria. The former of these is the more common. The sides of its face are golden yellow, set with black hair; whereas in C. vomitoria the sides of the face are black, but the hair is golden. Both are handsome, sturdy-looking diptera, with bluish-black thoraces, and abdomens of a dark metallic gun-metal sort of colour.
Blow-flies deposit their eggs on fresh or decaying flesh, and this is one of the great sources of trouble to the officers of the Army Service Corps. But they are not content with killed flesh. They will lay their eggs on any living flesh which is exposed, or in sores or tumours, and here their larvae will thrive. Dr. Graham-Smith tells us he once found the exposed muscles of the broken leg of a living rabbit seething with a mass of small blow-fly larvae, which were nourishing themselves upon the living tissues.
FIG. 25.—Blow-fly or blue-bottle, Calliphora erythrocephala, female (× 3). Antenna. Male head, dorsal view. Side view of head. Natural size, resting position. (From Graham-Smith.)
The eggs of the blow-fly hatch out in from ten to twenty hours in normal British temperatures; the larval life, in its three stages, lasts from seven to eight and a half days; the pupa state lasts a fortnight, so that the total development extends a day or two over three weeks. The maggots are unusually voracious; and Linnaeus used to say that the progeny of three blow-flies will dispose of a dead horse as quickly as three lions.
C. erythrocephala is essentially an outdoor fly and enters houses only in search of a nidus on which to deposit its eggs. C. vomitoria resembles its congener in size and habits, but it is not so abundant. Occasionally its eggs have been known to be deposited in the nostrils of animals and men.
But there are:—
All species of resplendent flies,
Some with green bodies and green eyes,
Pricking like pins’ heads from their holes
Like tiny incandescent coals.
(ANON.)
FIG. 26.—Green-bottle, Lucilia caesar, male (× 3). Antenna. Female head, dorsal view. Natural size, resting position. (From Graham-Smith.)
One of these, Lucilia caesar, is a marked nuisance to those responsible for victualling a camp. This green-bottle fly, like the Calliphora and the house-fly, belongs to the family Muscidae, and its larvae are said to be indistinguishable from those of blue-bottles. Some species of Lucilia deposit their eggs in great quantities amongst the wool of sheep when the sheep are ill-kept, and they do much damage. But as far as war is concerned the harm that Lucilia does is laying its eggs upon dead animals. It does this on all sorts of meat-stores; but in times of peace it especially infests stale fish, which the issuing larva very soon eat clean to the bone. When feeding upon a dead fish lying upon a beach they burrow down in the sand below their food. They descend some two to six inches, and for the most part remain deep in the sand during the daytime, coming up to feed at night. They also have a habit of migrating from one fish to another. This fly has also been known to lay its eggs in the neglected wounds of human beings.
FIG. 27.—Flesh-fly (Sarcophaga carnaria), female (× 3). Antenna. Natural size, resting position. (From Graham-Smith.)
Sarcophaga carnaria is another species which occasionally infests human sores, and which enters houses in search of filth or carrion on which to lay its eggs; it is viviparous and produces not eggs but live larvae. One female can give birth to 20,000 young; and Redi states that the larvae of these flesh-flies will in twenty-four hours devour so much food and grow so quickly that they increase their weight two-hundredfold.
Finally, there is a group of flies whose larvae penetrate under the skin of human beings and give rise to definite subcutaneous troubles. But, fortunately, these are, with few exceptions, confined to the warmer regions of the earth, and there is very little risk of their causing real trouble in Northern or Central Europe.
FIG. 28.—Side view of blow-fly (Calliphora erythrocephala) (× 5). A, Cheek (jowl); B, squama; C, halter. (From Graham-Smith.)
The troubles or diseases caused by the presence of fly larvae in the body are grouped in medical language under the term ‘myiasis,’ which Graham-Smith defines as follows:—
‘The term myiasis signifies the presence of dipterous larvae in the living body (whether of man or animals), as well as the disorders (whether accompanied or not by the destruction of tissue) caused thereby. Though not strictly coming within this definition, the sucking of blood by larvae through punctures of the skin, which they themselves produce, may be included for the sake of convenience in classification.
Myiasis in man may be produced by dipterous larvae:—
(a) Sucking blood through punctures in the skin (Auchmeromyia luteola).
(b) Deposited in natural cavities of the body (Chrysomyia, Lucilia, Sarcophaga, Calliphora, Oestrus).
(c) Deposited in neglected wounds (Chrysomyia, Lucilia, Sarcophaga, Calliphora).
(d) Living in subcutaneous tissue (Cordylobia, Dermatobia, Bengalia (?), Hypoderma).
(e) Passing through the alimentary canal (Fannia, Musca, Eristalis, Syrphus, Gastrophilus).
In the above list, only the more common genera producing myiasis are mentioned. In England, Type (e) is fairly common, and Types (b) and (c) are occasionally observed.’
We may now consider in detail, but very shortly, the categories set forth by Dr. Graham-Smith:—
(a) The very peculiar blood-sucking maggot known as the Congo-floor-maggot—the larva of Auchmeromyia luteola—fortunately does not spread beyond tropical and sub-tropical Africa. It chiefly affects the natives who sleep on mats.
(b) The flies which deposit their ova and larvae in the cavities of the body are again mostly foreign. The worst of all is the screw-worm (Chrysomyia macellaria) of the Southern States, Central and South America. Although it extends to Canada it is not troublesome north of Texas.
Occasionally, blow-flies in Great Britain deposit their ova in the human nose or ear. They very rapidly hatch and cause great inflammation and necrosis until they can be discharged or removed. They have even been found in the anterior chamber of the eye; and I have some microscopic sections showing the presence of these larvae in that chamber, whither they had probably proceeded from the nasal sinuses. But on the whole, cases of this sort are comparatively rare, and cause but little trouble.
(c) The real difficulty, and one which late last summer proved a serious trouble to our army in the field, are the cases in which maggots were found in neglected wounds. Here, however, we may take some comfort in the fact that the trouble is fortunately much greater in the tropical and sub-tropical regions than in more temperate climates, and diminishes as the cold weather draws on. Still, during the hot weeks of last August there were cases of wounded soldiers left lying on the fields for two or three days who were found to be suffering in this way. One almost hesitates to offer suggestions to our heroes in such cruel conditions; but whenever and wherever it can be done wounds should as far as possible be kept covered.
Not only are neglected wounds affected, but tumours and ulcers are often attacked. But, as I have said, the danger is much greater in warmer climates. We know that Herod Agrippa ‘was eaten of worms, and gave up the ghost’: a fact which recalls the translation given by an undergraduate in difficulties with the Acts of the Apostles in the ‘Little-Go’ who rendered ‘καì γενóμενος σκωληκóβρωτος ἐξέψυξεν’ ‘He became a Skolekobrote, and died in the enjoyment of that office.’
(d) Flies burrowing in the subcutaneous tissues are again very much commoner in tropical climates than in Northern Europe, and the cases quoted in our country are comparatively rare.
(e) The presence of larvae in the alimentary canal of man is by no means uncommon. Both the larvae of Musca and Fannia are not infrequently found; and over a thousand of the latter have been passed by a highly infected individual at one time. They probably make their way into the body with over-ripe fruit. In some cases they give rise to no symptoms, but in others violent pains are felt and a certain dizziness, and the digestive functions are interfered with. The presence of these larvae in the urinary passages is even more difficult to explain, but they undoubtedly are at times found in these channels.
A few years ago an elaborate investigation was carried on by Mr. W. Nicol, for the Local Government Board, on the part played by flies in the dispersal of the eggs of parasitic worms. He showed quite definitely that the ova of certain human parasites are taken into the fly and pass through its body undigested. Should these be deposited on the food of man, there is great risk of his becoming infected. As I have said before, flies take only liquid food, and it is only when the ova of the parasites are very small that they can pass into their alimentary canals. Some eggs are too large for the fly to swallow. Eggs of parasitic worms have also been shown to be carried on the legs and proboscides of flies, and these are deposited on the spot where the fly next cleans itself. Probably, however, in the end little harm is really done by flies in disseminating parasitic worms, but it is a possibility which must not be altogether disregarded.
The remedial measures for the control of flies are fully dealt with in Graham-Smith’s admirable book, ‘Flies in Relation to Disease,’ from which I have ventured to borrow many figures; and again by Dr. Gordon Hewitt, in his work on ‘House-flies,’ which has had such a wonderful success in stimulating our North-American cousins to decrease the numbers of one of the gravest enemies to mankind.
It has been shown over and over again that we can control the mosquito: the building of the Panama Canal alone proves this. We could equally control the ‘Infinite Torment of Flies.’ The Canadians and Americans are doing their best; but are we? The knowledgeable world has at least discovered the reason why Beelzebub was called the ‘Lord of flies.’