CHAPTER III

SOME OTHER FLIES AND THEIR DIVERSE HABITS

Just as the common "house-fly" and the "lesser house-fly" are often in error regarded as the same species with an insignificantly small difference of size, so the identity of each in turn may be confused with several other species which are not uncommon, but they are all normally outdoor flies.

The chief of these is the excessively common stable-fly, _Stomoxys calcitrans_, whose generic and specific designations are well given, for they mean "sharp-mouth," "kicking," the latter word denoting the action of the tormented horse; it has a long, thin, stiff, skin-piercing, shining black trunk, furnished with two lancets. It is an eager blood sucker. In size and colour it rather resembles the house-fly, but anyone who is keen sighted will recognise it at once by its bayonet-like trunk, held projecting prominently in front of its head. It is much addicted to basking outdoors on sunny walls, but on the approach of darkness or of inclement weather it will occasionally seek shelter indoors. Its wing pattern rather resembles that of the common house-fly, as has been previously explained.

Round about dairy farms _Hæmatobia stimulans_, a fly slightly smaller than the stable-fly, with a striped thorax and a blood-sucking trunk, will often leave the cattle to assail humanity. A still smaller, somewhat hairy, muscid type of fly, _Lyperosia irritans_, is also a common aggressor of oxen throughout the summer.

_Musca corvina_, the raven-fly, is smaller than the house-fly; it has very distinct dark markings; the abdomen of the female is chequered, but that of the male has a black central stripe on a yellowish abdomen. It frequents gardens, parks, and meadows. It is much less prolific than the house-fly, with which it shares the sweat-fly pestering habit.

_Cyrtoneura simplex_ is a little smaller and more common than the species last mentioned; its larvæ are bred in the dung of cows and other animals which it very severely pesters. However, many species of dung-bred flies do not in the least participate in the cattle-pestering habit.

The _Anthomyidæ_ are a family of about 250 small and medium sized garden frequenting and country flies, mainly of flower and honey seeking habits. Nevertheless, some are dung-frequenting; none are blood-sucking, but several are cattle-pestering sweat-flies, which, even more pertinaciously than the house-fly, will circle round one's head and repeatedly buzz against one's face. Of these, the small _Hydrotœa irritans_ and _Hy. dentipes_ are amongst the worst offenders. A few of the _Anthomyidæ_ are vegetarian garden pests; the larvæ of the cabbage-fly, the root-fly, the onion-fly and the celery-fly are, in some seasons, very destructive. The so-called "turnip-fly" is a small striped beetle of the same genus, _Phillotreta_, as the unstriped "flea-beetle" of the hop-fields. The larvæ of the majority of the species of the family of _Anthomyidæ_ are, more or less, feeders on decadent vegetable matter, but some, like those of the genus _Fannia_, are preferentially feeders on dung. The female of the latrine fly, _Fannia scalaris_, so closely resembles the lesser house-fly that only the expert with a magnifying glass, after a careful examination, can tell which is which; the male differs from the male of the lesser house-fly by being without the yellowish patches on the abdomen.

There is a larger and less common muscid fly, with an ashy-grey body, but with reddish legs, named by entomologists _Muscina stabulans_, which not only in body colour, but also in the pestering habit, resembles the house-fly; its Latin specific name is rather objectionable as too suggestive of the common "stable-fly," which name belongs to _Stomoxys calcitrans_ above-mentioned; its larvæ have been found in cow-dung, but they can also flourish on vegetarian fare.

The common blue-bottle is now named _Calliphora erythrocephala_ (red-head), and it can be recognised by its reddish face and black hairs for a beard, whilst the less common blue-bottle, named _Calliphora vomitoria_, may be said to have a reddish beard upon a black face; the latter has the blue colour more evenly distributed over the abdomen, whereon the former has dark markings.

_Polietes lardaria_ is a fly sometimes mistaken for the blue-bottle; its specific name is rather too suggestive of resemblance in habit. It may be recognised by its having four black stripes on the thorax, by its large white squamæ, and its tesselated glaucous abdomen; its wing pattern classifies it as belonging to the _Anthomyidæ_, whilst the true blue-bottles belong to the _Muscidæ_, and the grey blow-flies to a section (_Sarcophagina_) of the _Tachinidæ_.

There are some other outdoor flies which are not very dissimilar to the common blue-bottle, but they are more soberly coloured, ranging from bluish black to speckled and tinted greys; some of these have a pattern on the shiny upper surface of the abdomen which is conspicuously and beautifully chequered. Closely akin to these latter is the large grey blow-fly, or flesh-fly, _Sarcophaga carnaria_; it is much referred to in entomological books as of marvellous fecundity. The female deposits not eggs in a few hundreds, but already hatched maggots to the number of many thousands. Amongst half-a-dozen rarer kinds of smaller grey blow-flies the females differ in their striped markings, but their respective males seem quite indistinguishable apart.

Notwithstanding the prodigious fecundity of the grey blow-fly, the credit of being a practically useful scavenger of carrion must be given only to the blue-bottle, which is of a more robust habit, and which so promptly monopolises available matter that _Sarcophaga carnaria_ and her congeners are sometimes, perforce, compelled to give their larvæ a mere vegetarian diet.

The yellow cow-dung fly, _Scatophaga stercoraria_, is inoffensive, and one of the commonest flies observable in the course of a country-side ramble. It and its congeners are distinct in habits and appearance from any of the other flies above-mentioned. In this species the male is larger than the rather more smooth and dull-coloured female. Its body is furry but slender; it has small eyes and head parts. In repose it holds its wings parallel close above the abdomen, more like the "breeze-flies," or true "gad-flies," than the ordinary muscid flies. Although its proboscis does not seem as formidable as that of more insectivorous flies, yet it may sometimes be observed pouncing upon some small fly, which it holds with its powerful legs. This fly does not appear to be very predaceously inclined; perhaps it is only "acting a part," like some other creatures, including the amorous male of the common frog, which, failing to secure a more natural and complacent "partner in the dance," will in springtime seize upon and very persistently cling to an astonished carp.

Amongst many flies with bodies favoured with a brilliant metallic sheen, several species of green-bottle flies (_Luciliæ_) are notorious. Of these latter _L. Cæsar_ is the most common, but _L. Sericata_ is by far the worst in England, not uncommonly laying eggs upon sheep; many are of a brilliant golden green, but some vary towards a coppery green; all have red eyes and silvery faces. In summer-time these flies seize every opportunity of depositing their eggs upon any sores or skin wounds of animals; their larvæ normally feed on carrion and dung. The green-bottle, like the blue-bottle flies, are fond of both sweets and filth, but they do not pester wholesome animals as do the sweat-flies.

Next to the _Muscidæ_ the most often observed and easily recognisable as a distinct family of flies are the _Syrphidæ_, which include the "hover-flies," the drone-flies (often mistaken for the male of the hive-bee), and a number of other very common flies of a generally similar full-bodied shape, in most of which colour stripes and bands more or less suggest a comparison with wasps. The numerous species native to Great Britain are widely distributed, and, excepting the rare and very hairy _Merodon narcissi_, of which the larvæ feed on liliaceous bulbs, none is injurious and some are beneficial. Nearly all the flies of this family frequent flowers. The habit of many to hover for hours about a favoured spot, as if for mere pleasure, is remarkable; but it is not generally recognised that some of these hover-flies (of the genus _Syrphus_) are hawking for winged aphides and other small insects, which they quickly suck dry and drop whilst still on the wing. Many of the flower-frequenting _Syrphidæ_ are great devourers of pollen; all have strongly developed suctorial mouth parts.

The larvæ of the various syrphid flies differ greatly in appearance and habit; some are terrestrial; some aquatic; some semi-aquatic; some feed on decadent vegetation; some on sewage and filth, and some are insectivorous. Most useful to the horticulturist are those of the genus _Syrphus_, which feed on green-fly and other aphides. The most curious in shape are the "rat-tail" maggots of the common drone-fly, _Eristalis tenax_ (also others of allied genera), which can extend their long tubular tails and breathe atmospheric air through the same whilst lying under water. The larvæ of the genus _Volucella_ are found dwelling in the nests of bumble-bees and wasps; it is rather uncertain how far they are commensal, or parasitic, or devourers of dead matter. Some of the syrphid flies are single-brooded, but some at least are double or treble-brooded in the year; records are wanting about many, and which, if any other than the common drone-fly, are multi-brooded. Anyhow, none appears to breed in Great Britain as rapidly as do the house-fly, the blue-bottle, and other muscid flies.

The larvæ of _Conops flavipes_ are parasitic in the body of the adult bumble-bee, and they pupate therein.

The small family of the _Stratiomyidæ_ contains a few fairly common species called soldier-flies; these are interesting as linking _Orthorrhapha_ with _Cyclorrhapha_; their larvæ are some aquatic (the star-tailed maggots), others terrestrial, and some have hard shell-like skins; but they are not so curiously like a creeping marine limpet as are those belonging to the genus _Microdon_ (of the _Syrphidæ_), which are rare and wonderful dwellers in ants' nests.

There is a curiously shaped race of parasitic flies which cling to the host like a louse, called _Hippoboscidæ_; these have more than the usual provision of claws to their feet, both in the number (normally two) and size of the claws. The forest or spider-fly attaches itself to some part of the body out of reach of the horse's tongue. The ked, tick, or sheep louse-fly has a similar mode of life, and, after selecting its host, it becomes wingless. These flies, strange to say, nurse and nourish their larvæ within the oviduct, and, when one might think that they were laying their eggs, they are depositing pupæ or larvæ just ready to pupate. There are some species of the family of the louse-flies which infest birds.

The true gad-flies of the family of _Tabanida_ were, and sometimes still are called "blinden breeze-flies," and sometimes dun-flies; by a very easy mistake the countryman's word "blinden" (blind) has got changed by authors in books to "blinding," which is nonsense, and misses a wonderful instance of old-folk knowledge; the females are amongst the most inveterate blood-sucking flies, but the males are mere idle loiterers in summer sunshine on flowers; the eggs are laid on herbage in moist situations; the maggots and pupæ of many of these species are said "to be found in the soil," and some, if not all the larvæ, are predaceous, attacking worms and underground larvæ of various insects. They are more or less midsummer flies and are single-brooded. There are several largeish species (of the genera _Tabanus_ and _Therioplectes_) found in Great Britain, and they are diversely distributed, being respectively woodland, moorland, lowland, and highland inhabitants. The great ox-gad-fly is as large as a bumble-bee, though more long than broad in body, but the term gad-fly is often wrongly given to the worble-fly, which is really more bee-like, being furry and rounder in body. The genus _Hæmatopota_ comprises three smaller sized extra vicious blood suckers, _H. pluvialis_, rather common, _H. italica_, very local, and _H. crassicornis_, darker in colour and with spotted and dark tinted wings. Several of the large gad-flies have dull-tinted wings. They have large, shallow, brightly shining and curiously banded compound eyes, but no "ocelli"; they all seem to be at least semi-blind, and the females are rather sluggish, except between the hours of 11 a.m. and 5 p.m. in bright midsummer sunshine. The females hunt entirely by scent and are easily captured when attacking human beings; they alight on their victims with a stealthy silent approach. They appear unable to discriminate between clothing and bare skin as suitable spots for feeding. Amongst a band of mountaineering pedestrians, on a sunny day, it was observable that there would be a dozen or more "blinden breeze-flies" settling on the back of one, whilst the rest of the party were only favoured now and then by one or two apiece. It was apparently the smell of the "home-spun" coat which attracted; the colour of the garment did not seem to be the cause of the selection. Sunshine loving flies prefer white and pale colours. If a dog could speak, he would explain the smell of some "finished" cloth, but, for the sake of the fastidious, the secret is not here disclosed.

Very closely allied to the true breeze-flies in habit of life are the species of the genus _Chrysops_, of which two only are often met with in England, namely _Ch. cœcutiens_ and _Ch. relicta_; these flies are very keen blood suckers; they are smaller, slightly more slender and brighter coloured than the commoner _Tabanidæ_; it is characteristic of the genus _Chrysops_ that the antennæ are quite twice the length of the remarkably short horns of the majority of common full-bodied flies; all the species possess beautiful golden glittering eyes (whence the name _Chrysops_), and their wings are spotted and tinted.

One of the most horribly disgusting but serious facts connected with flies is observable most conspicuously amongst the wondrous family of the _Œstrida_. These pass the larval stage of life, not on, but inside the bodies of living animals; and the perfect insect, strange to say, is absolutely destitute of a mouth opening. Much misrepresentation has been prevalent, based entirely upon surmise, connecting "myiasis" in mankind, which is various but very rare, with the common infliction of horses and horned cattle with _Œstrid_ maggots. Myiasis is the medical term given to all the various forms of animal infliction by internal parasitic maggots, and this subject is reserved for discussion in the next chapter.

The characteristics and natures of the very numerous tribes and families of other kinds of flies will be found summarised in the Appendix of this booklet.