Chapter VIII: Hemiptera, or Bugs—anoplura 532 (20)

FAM. 14. LEPTIDAE, including XYLOPHAGIDAE and COENOMYIIDAE.—_The Leptidae proper are flies of feeble build; antennae with three joints and a terminal bristle; in the Xylophagidae the antennae are longer, and the third joint is complex. The wings have five posterior cells, the middle tibiae are spined. Pulvilli and a pulvilliform empodium present._ The three families are considered distinct by most authors, but there has always been much difficulty about the Xylophagidae and Coenomyiidae, we therefore treat them as sub-families.

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The Xylophaginae are a small group of slender Insects, perhaps most like the short-bodied kinds of Asilidae; the third joint of the antenna is vaguely segmented, and there is no terminal bristle. _Rhachicerus_ is a most anomalous little fly with rather long stiff antennae of an almost nemocerous character, the segments of which give off a short thick prolongation on each side, reminding one of a two-edged saw. The three or four British species of Xylophaginae are forest Insects, the larvae of which live under bark, and are provided with a spear-like head with which they pierce other Insects. The Coenomyiinae consist of the one genus _Coenomyia_, with two or three European and North American species. They are remarkably thick-bodied, heavy flies, reminding one somewhat of an imperfect Stratiomyid destitute of ornamentation. The metamorphosis of _C. ferruginea_ has been described by Beling.[401] The larva is not aquatic, but lives in burrows or excavations in the earth where there are, or have recently been, rotten logs; it is probably predaceous. It is cylindric, with an extremely small head and eleven other segments, the stigma on the first thoracic segment distinct; the terminal segment is rather broad, and the structures surrounding the stigma are complex. The pupa has stigmata on each of abdominal segments 2 to 8. Notwithstanding that the fly is so different to _Xylophagus_, the larvae indicate the two forms as perhaps really allied. One of the Leptinae, _Atherix ibis_, has a singular mode of oviposition (Fig. 227), the females of the species deposit their eggs in common, and, dying as they do so, add their bodies to the common mass, which becomes an agglomeration, it may be of thousands of individuals, and of considerable size. The mass is attached to a branch of a bush or to a plant overhanging water, into which it {481}ultimately falls. These curious accumulations are occasionally found in England as well as on the Continent, but no reason for so peculiar a habit is at present forthcoming. Still more remarkable are the habits of some European Leptids of the genera _Vermileo_ (_Psammorycter_ of some authors) and _Lampromyia_, slender rather small flies of Asilid-like appearance, the larvae of which form pit-falls after the manner of the Ant-lion. According to Beling[402] the larva of _Leptis_ is very active, and is distinguished by having the stigmatic orifice surrounded by four quite equal, quadrangularly placed prominences; and at the other extremity of the body a blackish, naked, triangular plate; on the under side of each of seven of the abdominal segments there is a band of spines. The larva of _Atherix_ has seven pairs of abdominal feet. Altogether there are some two or three hundred known species of Leptidae; our British species scarcely reach a score. They are destitute of biting-powers and are harmless timid creatures. _Leptis scolopacea_, the most conspicuous of our native species, a soft-bodied fly of rather large size, the wings much marked with dark colour, and the thick, pointed body yellowish, marked with a row of large black spots down the middle, is a common Insect in meadows.

FAM. 15. TABANIDAE (_Breeze-flies_, _Cleggs_, or _Horse-flies_, also frequently called _Gad-flies_).—_Proboscis fleshy, distinct, enwrapping pointed horny processes, palpi distinct, terminal joint inflated, pendent in front of proboscis. Antennae projecting, four-jointed, second joint very short, third variable in form, fourth forming an indistinctly segmented continuation of the third, but not ending in a bristle. A perfect squama in front of the halter. Eyes large, very large in the males, but laterally extending, rather than globose._

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This large and important family of flies, of which Williston states that 1400 or 1500 species are named, is well known to travellers on account of the blood-sucking habits of its members; they have great powers of flight, and alight on man and animals, and draw blood by making an incision with the proboscis; only the females do this, the males wanting a pair of the lancets that enable the other sex to inflict their formidable wounds. They are comparatively large Insects, some of our English species of _Tabanus_ attaining an inch in length. The smaller, grey _Haematopota_, is known to every one who has walked in woods or meadows in the summer, as it alights quietly on the hands or neck and bites one without his having previously been made aware of its presence. The larger Tabani hum so much that one always knows when an individual is near. The species of _Chrysops_, in habits similar to _Haematopota_, are remarkable for their beautifully coloured golden-green eyes. In Brazil the Motuca fly, _Hadrus lepidotus_, Perty, makes so large and deep a cut that considerable bleeding may follow, and as it sometimes settles in numbers on the body, it is deservedly feared. The most remarkable forms of Tabanidae are the species of the widely distributed genus _Pangonia_ (Fig. 229). The proboscis in the females of some of the species is three or four times the length of the body, and as it is stiff and needle-like the creature can use it while hovering on the wing, and will pierce the human body even through clothing of considerable thickness. The males suck the juices of flowers. The Seroot fly, that renders some of the districts of Nubia uninhabitable for about three months of the year, appears, from the figure and description given by Sir Samuel Baker, to be a _Pangonia_. Tabanidae are a favourite food of the fossorial wasps of the family Bembecidae. These wasps are apparently aware of the blood-sucking habits of their favourites, and attend on travellers and pick up the flies as they are about to settle down to their phlebotomic operations. The larvae of the Tabanidae are some {483}of them aquatic, but others live in the earth or in decaying wood; they are of predaceous habits, attacking and sucking Insect-larvae, or worms. Their form is cylindric, attenuate at the two extremities; the slender small head is retractile, and armed with a pair of conspicuous, curved black hooks. The body is surrounded by several prominent rings. The breathing apparatus is apparently but little developed, and consists of a small tube at the extremity of the body, capable of being exserted or withdrawn; in this two closely approximated stigmata are placed. In a larva, probably of this family, found by the writer in the shingle of a shallow stream in the New Forest, the annuli are replaced by seven circles of prominent pseudopods, on the abdominal segments about eight in each circle, and each of these feet is surmounted by a crown of small hooks, so that there are fifty or sixty feet distributed equally over the middle part of the body without reference to upper or lower surface. The figures of the larva of _T. cordiger_, by Brauer, and of _Haematopota pluvialis_, by Perris, are something like this, but have no setae on the pseudopods. The metamorphoses of several Tabanidae are described and figured by Hart;[403] the pupa is remarkably like a Lepidopterous pupa. We have five genera and about a score of species of Tabanidae in Britain.

A, the larva, × 3; B, head; C, end of body; D, one of the pseudopods. New Forest.]

FAM. 16. ACANTHOMERIDAE.—A very small family of two genera (_Acanthomera_ and _Rhaphiorhynchus_) confined to America, and including the largest Diptera, some being two inches long. The antenna is terminated by a compound of seven segments and a style; the proboscis is short, and the squama rudimentary. The general form reminds one of Tabanidae or Oestridae. A dried larva exists in the Vienna collection; it is amphipneustic, and very remarkable on account of the great size of the anterior stigma.

{484}FAM. 17. THEREVIDAE.—_Moderate-sized flies, with somewhat the appearance of short Asilidae. They have, however, only a feeble fleshy proboscis, and minute claws, with pulvilli but no empodium; the antennae project, are short, three-jointed, pointed._—The flies of this family are believed to be predaceous like the Robber-flies, but they appear to be very feebly organised for such a life. We have about ten species in Britain, and there are only some 200 known from all the world. But little is known as to the metamorphoses. Meigen found larvae of _T. nobilitata_ in rotten stumps, but other larvae have been recorded as devouring dead pupae or larvae of Lepidoptera. The larvae are said to be elongate, very slender, worm-like, and to have nineteen body-segments, the posterior pair of spiracles being placed on what looks like the seventeenth segment, but is really the eighth of the abdomen. The pupa is not enclosed in the larval skin; that of _Psilocephala_ is armed with setae and spinous processes, and was found in rotten wood by Frauenfeld.

FAM. 18. SCENOPINIDAE.—_Rather small flies, without bristles. Antennae three-jointed, the third joint rather long, without appendage. Proboscis not projecting. Empodium absent._ These unattractive flies form one of the smallest families, and are chiefly found on windows. _S. fenestralis_ looks like a tiny Stratiomyid, with a peculiar, dull, metallic surface. The larva of this species has been recorded as feeding on a variety of strange substances, but Osten Sacken is of opinion[404] that it is really predaceous, and frequents these substances in order to find the larvae that are developing in them. If so, _Scenopinus_ is useful in a small way by destroying "moth," etc. The larva is a little slender, cylindrical, hard, pale worm of nineteen segments, with a small brown head placed like a hook at one extremity of the body and with two short, divergent processes at the other extremity, almost exactly like the larva of _Thereva_. Full references to the literature about this Insect are given by Osten Sacken.

FAM. 19. NEMESTRINIDAE.—These Insects appear to be allied to the Bombyliidae. _They are of medium size, often pilose, and {485}sometimes with excessively long proboscis; antennae short, with a simple third joint, and a jointed, slender, terminal appendage; the tibiae have no spurs, the empodium is pulvillus-like. The wing-nervuration is perhaps the most complex found in Diptera, there being numerous cells at the tip, almost after the fashion of Neuroptera._ With this family we commence the aerial forms composing the Tromoptera of Osten Sacken. Nemestrinidae is a small family of about 100 species, but widely distributed. _Megistorhynchus longirostris_ is about two-thirds of an inch long, but has a proboscis at least four times as long as itself. In South Africa it may be seen endeavouring to extract, with this proboscis, the honey from the flower of a _Gladiolus_ that has a perianth just as long as its own rostrum; as it attempts to do this when it is hovering on the wing, and as the proboscis is, unlike that of the Bombylii, fixed, the Insect can only succeed by controlling its movements with perfect accuracy; hence it has great difficulty in attaining its purpose, especially when there is much wind, when it frequently strikes the earth instead of the flower. M. Westermann thinks[405] the life of the Insect and the appearance and duration of the flower of the _Gladiolus_ are very closely connected. The life-history of _Hirmoneura obscura_ has recently been studied in Austria by Handlirsch and Brauer.[406] The larva is parasitic on the larva of a Lamellicorn beetle (_Rhizotrogus solstitialis_); it is metapneustic, and the head is highly modified for predaceous purposes. The young larva apparently differs to a considerable extent from the matured form. The most curious fact is that the parent fly does not oviposit near the Lamellicorn-larva, but places her eggs in the burrows of some wood-boring Insect in logs; the larvae when hatched come to the surface of the log, hold themselves up on their hinder extremity and are carried away by the wind; in what manner they come into contact with the Lamellicorn larva, which feeds in turf, is unknown. The pupa is remarkable on account of the prominent, almost stalked stigmata, and of two pointed divergent processes at the extremity of the body. This life-history is of much interest, as it foreshadows to some extent the complex parasitic life-histories of Bombyliidae. The Nemestrinidae are not represented in the British fauna.

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FAM. 20. BOMBYLIIDAE.—_Body frequently fringed with down, or covered in large part with hair. Legs slender, claws small, without distinct empodium, usually with only minute pulvilli. Proboscis very long or moderate, antennae three-jointed, terminal joint not distinctly divided, sometimes large, sometimes hair-like._ This is a very large family, including 1500 species, and is of great importance to both naturalist and economist. Two well-marked types, formerly treated as distinct families, are included in it—(1) the Bombyliides with very long exserted rostrum, and humped thorax; and (2) Anthracides, with a short beak, and of more slender and graceful form. None of these flies are bloodsuckers, they frequent flowers only, and use their long rostrums in a harmless manner. The members of both of these groups usually have the wings ornamented with a pattern, which in _Anthrax_ is frequently very remarkable; in both, the clothing of the body is frequently variegated. Their powers of flight are very great, and the hovering _Bombylius_ of early spring is endowed with an unsurpassed capacity for movement, remaining perfectly still on the wing, and darting off with lightning rapidity; _Anthrax_ is also most rapid on the wing. In Britain we have but few species of Bombyliidae, but in warm and dry climates they are very numerous. The life-history of these Insects was till recently unknown, but that of _Argyromoeba_ (_Anthrax_) _trifasciata_ has been described by the French naturalist, Fabre, who ascertained that the species is parasitic on the Mason-bee, _Chalicodoma muraria_, that forms nests of solid masonry. He endeavoured to discover the egg, but failed; the parent-fly oviposits, it appears, by merely dropping a minute egg while flying over the surface of the mass of masonry by which the grubs of the _Chalicodoma_ are protected. From this egg there is hatched a minute delicate vermiform larva (Fig. 232, A). In order to obtain its food, it is necessary for this feeble creature to penetrate the masonry; apparently a hopeless task, the animal {487}being scarcely a twentieth of an inch long and very slender; it is, however, provided with a deflexed horny head, armed in front with some stiff bristles, while on the under surface of the body there are four pairs of elongate setae serving as organs of locomotion; thus endowed, the frail creature hunts about the surface of the masonry, seeking to find an entrance; frequently it is a long time before it is successful; but though it has never taken any food it is possessed of great powers of endurance. Usually, after being disclosed from the egg, it remains about fifteen days without stirring; and even after it commences its attempts to enter the nest it is still capable of a long life without taking any food. Possibly its organisation will not permit it to feed (supposing any food were obtainable by it) without its growing somewhat thereafter, and if so, its chance of obtaining entrance through the masonry would be diminished. Abstention, it would appear, is the best policy, whether inevitable or not; so the starving little larva continues its endeavours to find a chink of entrance to the food contained in the interior of the masonry. It has plenty of time for this, because it is better for it not to get into the cell of the bee until the grub is quite full grown, and is about to assume the pupal form, when it is quite incapable of self-defence. Finally, after greater or less delay, the persevering little larva succeeds in finding some tiny gap in the masonry through which it can force itself. M. Fabre says that the root of a plant is not more persistent in descending into the soil that is to support it than is this little _Anthrax_ in insinuating itself through some crack that may admit it to its food. Having once effected an entrance the organisation that has enabled it to do so is useless; this primary form of the larva has, in fact, as its sole object to enable the creature to penetrate to its food. Having penetrated, it undergoes a complete change of form, and appears as a creature specially fitted for feeding on the quiescent larva of the bee without destroying it. To accomplish this requires an extreme delicacy of organisation and instinct; to bite the prey would be to kill it, and if this were done, the _Anthrax_ would, Fabre supposes, ensure its own death, for it cannot feed on the dead and putrefying grub; accordingly, the part of its body that does duty as a mouth is merely a delicate sucker which it applies to the skin of the _Chalicodoma_-grub; and thus without inflicting any perceptible wound it sucks day {488}after day, changing its position frequently, until it has completely emptied the pupa of its contents, nothing being left but the skin. Although this is accomplished without any wound being inflicted, so effectual is the process that all the _Chalicodoma_ is gradually absorbed. The time requisite for completely emptying the victim is from twelve to fifteen days; at the end of this time the _Anthrax_-larva is full grown, and the question arises, how is it to escape from the cell of solid masonry in which it is imprisoned? It entered this cell as a tiny, slender worm through a minute orifice or crack, but it has now much increased in size, and exit for a creature of its organisation is not possible. For some months it remains a quiescent larva in the cell of the _Chalicodoma_, but in the spring of the succeeding year it undergoes another metamorphosis, and appears as a pupa provided with a formidable apparatus for breaking down the masonry by which it is imprisoned. The head is large and covered in front with six hard spines, to be used in striking and piercing the masonry, while the other extremity of the body bears some curious horns, the middle segments being armed with rigid hairs directed backwards, and thus facilitating movement in a forward direction and preventing slipping backwards. The pupa is strongly curved, and fixes itself by the aid of the posterior spines; then, unbending itself, it strikes with the armour of the other extremity against the opposing wall, which is thus destroyed piecemeal until a gallery of exit is formed; when this is completed the pupa-skin bursts and the perfect fly emerges, leaving the pupa-case still fixed in the gallery. Thus this species appears in four consecutive forms—in addition to the egg—each of which is highly specialised for the purposes of existence in that stage.

The habits of our British _Bombylius major_ have been partially observed by Dr. Chapman,[407] and exhibit a close analogy with those of _Anthrax trifasciata_. The bee-larva that served as food was in this case _Andrena labialis_, and the egg was deposited by the fly, when hovering, by jerking it against the bank in which the nest of the bee was placed.

It has recently been discovered that the larvae of various species of Bombyliidae are of great service by devouring the eggs of locusts. Riley found that the egg-cases of _Caloptenus {489}spretus_ are emptied of their contents by the larvae of _Systoechus oreas_ and _Triodites mus_. A similar observation has been made in the Troad by Mr. Calvert, who found that the Bombyliid, _Callostoma fascipennis_, destroys large quantities of the eggs of _Caloptenus italicus_. Still more recently M. Künckel d'Herculais has discovered that the destructive locust _Stauronotus maroccanus_ is kept in check in Algeria in a similar manner, as many as 80 per cent of the eggs of the locust being thus destroyed in certain localities. He observes that the larva of the fly, after being full fed in the autumn, passes the winter in a state of lethargy—he calls it "hypnody"—in the egg-case of the locust, and he further informs us that in the case of _Anthrax fenestralis_, which devours the eggs of the large _Ocnerodes_, the lethargy may be prolonged for a period of three years. After the pupa is formed it works a way out of the case by means of its armature, and then again becomes for some days immobile before the perfect fly appears. Lepidopterous larvae are also attacked by Bombyliid flies. A species of _Systropus_ has been recorded as destroying the larva of _Limacodes_. Several of the Bombyliids of the genus just mentioned are remarkable for the great resemblance they display to various Hymenoptera, some of them being very slender flies, like the thin bodied fossorial Hymenoptera. The difference between the pupa and imago in this case is very remarkable (Fig. 233).

FAM. 21. ACROCERIDAE or CYRTIDAE.—_Flies of the average size, of peculiar form, the small head consisting almost entirely of the eyes, and bent down under the humped thorax: wings small, halteres entirely concealed by the very large horizontal squamae; antennae very diverse._ The peculiar shape of these flies is an exaggeration of that we have already noticed in _Bombylius_. The mouth in Acroceridae is very variable; there may be a very long, slender proboscis (_Acrocera_), or the mouth-parts may be so atrophied that it is doubtful whether even an orifice exists (_Ogcodes_). There are but {490}few species known, and all of them are rare;[408] in Britain we have but two (_Ogcodes gibbosus_, _Acrocera globulus_). The genus _Pterodontia_, found in North America and Australia, an inflated bladder-like form with a minute head, is amongst the most extraordinary of all the forms of Diptera. The habits are very peculiar, the larvae, so far as known, all living as parasites within the bodies of spiders or in their egg-bags. It appears, however, that the flies do not oviposit in appropriate places, but place their eggs on stems of plants, and the young larvae have to find their way to the spiders. Brauer has described the larva of the European _Astomella lindeni_,[409] which lives in the body of a spider, _Cteniza ariana_; it is amphipneustic and maggot-like, the head being extremely small. The larva leaves the body of the spider for pupation; the pupa is much arched, and the head is destitute of the peculiar armature of the Bombyliidae, but has a serrate ridge on the thorax. Emerton found the larvae of an _Acrocera_ in the webs of a common North American spider, _Amaurobius sylvestris_, they having eaten, it was supposed, the makers of the cobwebs.

FAM. 22. LONCHOPTERIDAE.—_Small, slender flies, with pointed wings, short, porrect antennae, with a simple, circular third joint, bearing a bristle; empodium very small, pulvilli absent._—Only one genus of these little flies is known, but it is apparently widely distributed, and its members are common Insects. They have the appearance of Acalyptrate Muscidae, and the nervuration of the wing is somewhat similar, the nervures being simple and parallel, and the minute cross-nervures placed near the base. The systematic position is somewhat doubtful, and the metamorphoses are but incompletely known, very little having been added to what was discovered by Sir John Lubbock in 1862.[410] The larva lives on the earth under vegetable matter; it is very transparent, amphipneustic, with a peculiar head, and with fringes on the margins. This larva changes to a semi-pupa or apterous maggot-like form, within the larval skin; the true pupa was {491}not noticed by Lubbock, but Frauenfeld[411] has since observed it, though he only mentions that it possesses differentiated limbs and segments. The metamorphoses appear to be very peculiar. This fly requires a thorough study.

FAM. 23. MYDAIDAE.—_Large flies of elongate form; the hind femora long and toothed beneath; the antennae knobbed at the tip, projecting, rather long, the basal joint definite, but the divisions of the subsequent joints more or less indistinct. Empodium small. Wings frequently heavily pigmented; with a complex nervuration._ These fine flies are exotic; a few species occur in the Mediterranean region, even in the South of Europe; the chief genus, _Mydas_, is South American, but most of the other genera are Australian or African. But little is known as to the life-histories. The larvae are thought to live in wood, and to prey on Coleopterous larvae.

FAM. 24. ASILIDAE (_Robber-flies_).—_Mouth forming a short, projecting horny beak, the palpi usually only small; the feet generally largely developed; the claws large, frequently thick and blunt, the pulvilli generally elongate, the empodium a bristle; halteres free; no squama._ The Asilidae is one of the largest families of flies, and probably includes about 3000 described species: as will readily be believed, there is much variety of form; some are short and thick and extremely hairy, superficially resembling hairy bees, but the majority are more or less elongate, the abdomen being specially long, and having eight segments conspicuously displayed. The antennae are variable, but are three-jointed with a terminal appendage of diverse form and structure. They belong to the super-family Energopoda of Osten Sacken, but the association of Empidae and Dolichopidae with them does not seem to be very natural. In their perfect state these flies are most voracious, their prey being Insects, which they seize alive and impale with the rostrum. They are amongst the most formidable of foes and fear nothing, wasps or other stinging Insects being attacked and mastered by the stronger species without difficulty. They have been observed to capture even dragon-flies and tiger-beetles. As is the case with so many other Insects that prey on living Insects, the appetite in the Asilidae seems to be insatiable; a single individual has been observed to kill eight moths in twenty minutes. They have {492}been said to suck blood from Vertebrates, but this appears to be erroneous. The metamorphoses of a few species have been observed. Perris has called attention to the close alliance between the larvae of Tabanidae and of Asilidae,[412] and it seems at present impossible to draw a line of distinction between the two. So far as is known, the larvae of Asilidae are terrestrial and predaceous, attacking more particularly the larvae of Coleoptera, into which they sometimes bore; in _Laphria_ there are numerous pseudopods, somewhat of the kind shown in Fig. 230, but less perfect and without hairs; the head and breathing organs appear to be very different. According to Beling's descriptions of the larvae of _Asilus_, the head in this case is more like that of the figure, but there are no pseudopods. The flies of Asilidae and Tabanidae are so very distinct that these resemblances between their larvae are worthy of note.

FAM. 25. APIOCERIDAE.—_Moderate-sized flies marked with black and white, with an appearance like that of some Muscidae and Asilidae; with clear wings, the veins not deeply coloured; antennae short, with a short, simple appendage; no empodium._ But little is known as to the flies of this family, of which only two genera, consisting of about a dozen species, are found in North America, Chili, and Australia. Osten Sacken is inclined to treat them as an aberrant division of Asilidae. Brauer looks on them as primitive or synthetic forms of much interest, and has briefly described a larva which he considers may be that of _Apiocera_, but this is doubtful; it is a twenty-segmented form, and may be that of a _Thereva_.[413]

FAM. 26. EMPIDAE.—_Small or moderate-sized flies of obscure colours, grey, rusty, or black, with small head, somewhat globular in form, with three-jointed antennae, the terminal joint long and pointed; usually there is a long slender beak; the legs are elongate, frequently hairy; the tarsi bear long pulvilli and a small empodium._ The Empidae are an extensive family of flies, with predaceous habits, the rostrum being used by the female as an instrument for impaling and sucking other flies. They are occasionally very numerous in individuals, especially in wooded districts. There is great variety; there are nearly 200 species in Britain. The forms placed in the sub-family Hybotinae are curious slender little Insects, with very convex thorax and {493}large hind legs. In _Hemerodromia_ the front legs are raptorial, the femora being armed with spines on which the tibiae close so as to form a sort of trap. Many Empidae execute aërial dances, and some of the species of the genus _Hilara_ are notorious for carrying veils or nets in the form of silken webs more or less densely woven. This subject is comparatively new, the fact having been discovered by Baron Osten Sacken in 1877,[414] and it is not at all clear what purpose these peculiar constructions serve; it appears probable that they are carried by means of the hind legs, and only by the males. Mik thinks that in _H. sartor_ the veil acts as a sort of parachute, and is of use in carrying on the aërial performance, or enhancing its effect; while in the case of other species, _H. maura_ and _H. interstincta_, the object appears to be the capture or retention of prey, after the manner of spiders. The source of the silk is not known, and in fact all the details are insufficiently ascertained. The larvae of Empidae are described as cylindrical maggots, with very small head, and imperfect ventral feet; the stigmata are amphipneustic, the thoracic pair being, however, excessively small; beneath the posterior pair there is nearly always a tooth- or spine-like prominence present.

FAM. 27. DOLICHOPIDAE.—_Graceful flies of metallic colours, of moderate or small size, and long legs; usually with bristles on the thorax and legs, the halteres exposed, squamae being quite absent; antennae of two short stout joints (of which the second is really two, its division being more or less distinct), with a thread-like or hair-like appendage. Proboscis short, fleshy. Claws, pulvilli, and empodium small; wings with a simple system of nervures, those on the posterior part of the wing are but few, there is no anterior basal cross-vein between the discal and second basal cells, which therefore form but one cell._ This is also a very extensive family of flies, of which we have probably about 200 species in Britain. They are conspicuous on account of their golden, or golden-green colours, only a few being yellow or black. {494}The males are remarkable for the curious special characters they possess on the feet, antennae, face, or wings. These characters are not alike in any two species; they are believed to be of the nature of ornaments, and according to Professor Aldrich and others are used as such in courtship.[415] This family of flies approaches very closely to some of the Acalyptrate Muscidae in its characters. It is united by Brauer with Empidae to form the tribe Orthogenya. Although the species are so numerous and abundant in Europe, little is known as to their metamorphoses. Some of the larvae frequent trees, living under the bark or in the overflowing sap, and are believed to be carnivorous; they are amphipneustic; a cocoon is formed, and the pupa is remarkable on account of the existence of two long horns, bearing the spiracles, on the back of the thorax; the seven pairs of abdominal spiracles being excessively minute.[416]

SERIES 3. CYCLORRHAPHA ASCHIZA

FAM. 28. PHORIDAE.—_Small flies, with very convex thorax, small head, very small two-jointed antennae, bearing a long seta; femora more or less broad; wings with two dark, thick, approximate veins, meeting on the front margin near its middle, and besides these, three or four very fine veins, that run to the margins in a sub-parallel manner without forming any cells or forks._ This obscure family of flies is of small extent, but its members are extremely common in Europe and North America, where they often occur in numbers running on the windows of houses. It is one of the most isolated groups of Diptera, and great difference of opinion prevails as to its classification. The wing-nervuration is peculiar (but varies somewhat in the species), the total absence of any cross-veins even on the basal part of the wing being remarkable. There are bristles on the head and thorax, but they are not arranged in a regular manner. The larvae live in a great variety of animal and vegetable decaying matter, {495}and attack living Insects, and even snails, though probably only when these are in a sickly or diseased condition. The metamorphoses of several species have been described.[417] The larvae are rather slender, but sub-conical in form, with eleven segments and a very small head, amphipneustic, the body behind terminated by some pointed processes. The pupa is remarkable; it is contained in a case formed by the contracted and hardened skin of the larva; though it differs much in form from the larva the segmentation is distinct, and from the fourth segment there project two slender processes. These are breathing organs, attached to the prothorax of the imprisoned pupa; in what manner they effect a passage through the hardened larval skin is by no means clear. Perris supposes that holes for them pre-exist in the larval skin, and that the newly-formed pupa by restless movements succeeds in bringing the processes into such a position that they can pass through the holes. The dehiscence of the puparium seems to occur in a somewhat irregular manner, as in _Microdon_; it is never Cyclorrhaphous, and according to Perris is occasionally Orthorrhaphous; probably there is no ptilinum.

The Insect recently described by Meinert as _Aenigmatias blattoides_,[418] is so anomalous, and so little is known about it, that it cannot at present be classified. It is completely apterous; the arrangement of the body-segments is unlike that of Diptera, but the antennae and mouth-parts are said to be like those of Phoridae. The Insect was found near Copenhagen under a stone in the runs of _Formica fusca_. Meinert thinks it possible that the discovery of the male may prove _Aenigmatias_ to be really allied to Phoridae, and Mik suggests that it may be the same as _Platyphora lubbocki_, Verrall, known to be parasitic on ants. Dahl recently described a wingless Dipteron, found living as a parasite on land-snails in the Bismarck archipelago, under the name of _Puliciphora lucifera_, {496}and Wandolleck has recently made for this and some allies the new family Stethopathidae. It seems doubtful whether these forms are more than wingless Phoridae.

FAM. 29. PLATYPEZIDAE.—_Small flies, with porrect three-jointed antennae, first two joints short, third longer, with a terminal seta; no bristles on the back; hind legs of male, or of both sexes, with peculiar, broad, flat tarsi; the middle tibiae bear spurs; there is no empodium._ Platypezidae is a small family of flies, the classification of which has always been a matter of considerable difficulty, and is still uncertain. The larvae are broad and flat, fringed at the margin with twenty-six spines; they live between the lamellae of Agaric fungi. At pupation the form alters but little; the imago emerges by a horizontal cleft occurring at the margins of segments two and four.[419] We have four genera (_Opetia_, _Platycnema_, _Platypeza_, _Callomyia_), and nearly a score of species of Platypezidae in our British list, but very little seems to be known about them. There is much difference in the eyes of the sexes, in some at any rate of the species, they being large and contiguous in the male, but widely separated in the female.

FAM. 30. PIPUNCULIDAE.[420]—_Small flies, with very short antennae bearing a long seta that is not terminal; head almost globular, formed, except at the back, almost entirely by the large conjoined eyes; the head is only slightly smaller in the female, but in the male the eyes are more approximate at the top._ This is another of the small families of flies, that seems distinct from any other, though possessing no very important characters. In many of the flies that have very large eyes, the head is either flattened (_i.e._ compressed from before backwards, as in Tabanidae, Asilidae), or forced beneath the humped thorax (as in Acroceridae), but neither of these conditions exists in _Pipunculus_; in them the head extends far forwards, so that the area of the {497}eye compared with the size of the body is perhaps greater than in any other Diptera. The general form is somewhat that of _Anthrax_, but the venation on the hind part of the wing is much less complex. There is a remarkable difference between the facets on the front and the back of these great eyes. We have three genera and about a dozen species of Pipunculidae in Britain but apparently they are far from common Insects. What is known about the life-history is almost confined to an imperfect observation by Boheman, who found the larva of _P. fuscipes_ living after the manner of a Hymenopterous parasite in the body of a small Homopterous Insect.[421] The pupa seems to be of the type of that of Syrphidae.

FAM. 31. CONOPIDAE.—_Elegant flies of moderate size, of varied colours, with abdomen slender at the base, at the tip strongly incurved and thicker; antennae inserted close together on a prominence, three-jointed, first joint sometimes very short. The upper surface of the body without bristles or with but few. There is a slender, elongate proboscis, which is retractile and usually invisible._ This rather small family of flies includes some of the most remarkable forms of Diptera; it includes two divisions, the Conopinae with long antennae terminated by a very minute pointed process, and Myopinae with shorter antennae bearing a hair that is not placed at the end of the third joint. The former are the more wasp-like and elegant; the Myopinae being much more like ordinary flies, though they frequently have curious, inflated heads, with a white face. The mode of life of the larva of _Conops_ is peculiar, it being parasitic in the interior of _Bombus_, or other Hymenoptera. They have been found to attack _Bombus_, _Chalicodoma_, _Osmia_, _Vespa_, _Pompilus_, and other Aculeates. Williston says that Orthoptera are also attacked. _Conops_ has been seen to follow Bumble-bees and alight on them, and Williston says this act is accompanied by oviposition, the larva that is hatched boring its way into the body of the bee. Others have supposed that the flies enter the bees' nests and place their eggs in the larvae or pupae; but this is uncertain, for _Conops_ has never been reared from a bee-larva or pupa, though it has frequently been procured from the imago: cases indeed having been recorded in which _Conops_ has emerged from the body {498}of a _Bombus_ several months after the latter had been killed and placed in an entomologist's collection. The larva is broad, and when full grown apparently occupies nearly all the space of the interior of the abdomen of the bee; it has very peculiar terminal stigmata. The pupa is formed in the larval skin, which is greatly shortened and indurated for the purpose; this instar bears, in addition to the posterior stigmata, a pair of slightly projecting, anterior stigmata. We have several species of Conopidae in Britain; those belonging to the division Conopinae are all rare Insects, but the Myopinae are not so scarce; these latter are believed to be of similar habits with the Conopinae, though remarkably little is known about them. This is another of the numerous families, the relations of which are still a subject for elucidation. Brauer places the Conopidae in his section Schizophora away from Syrphidae, but we do not comprehend on what grounds; an inspection of the head shows that there is no frontal lunule as there is in Eumyiidae; both _Myopa_ and _Conops_ agreeing fairly well with _Syrphus_ as to this. We therefore place the family in its old position near _Syrphus_ till the relations with Acalypterate Muscidae shall be better established.

FAM. 32. SYRPHIDAE (_Hover-flies_).—_Of moderate or rather large size, frequently spotted or banded with yellow, with a thick fleshy proboscis capable of being withdrawn into a cleft on the under side of the head; antennae not placed in definite cavities, three-jointed (usually very short), and leaving a seta that is not terminal in position, and may be feathered. Squama variable, never entirely covering the halteres; the chief (third to fifth) longitudinal veins of the wings connected near their termination by cross-veins and usually thus forming a sort of short margin parallel with the hind edge of the wing; a more or less imperfect false nervure running between the third and fourth longitudinal nervures; no empodium and generally no distinct system of bristles on the back of the body._ The Syrphidae (Fig. 212) form one of the largest and best known of all the families of flies; they abound in our gardens where, in sunny weather, some species may be nearly always seen hovering over flowers, or beneath trees in places where the rays of the sun penetrate amidst the shade. There are two or three thousand species known, so that of course much variety exists; some are densely covered with hair (certain _Volucella_ and others), many are of elegant form, and some bear a {499}considerable resemblance to Hymenoptera of various groups. The peculiar veining of the wings permits of their easy identification, the line of two nervules, approximately parallel with the margin of the distal part of the wing (Fig. 212, D), and followed by a deep bay, being eminently characteristic, though there are some exceptions; there are a few forms in which the antennae are exceptional in having a terminal pointed process. The proboscis, besides the membranous and fleshy lips, consists of a series of pointed slender lancets, the use of which it is difficult to comprehend, as the Insects are not known to pierce either animals or vegetables, their food being chiefly pollen; honey is also doubtless taken by some species, but the lancet-like organs appear equally ill-adapted for dealing with it. The larvae are singularly diversified; first, there are the eaters of Aphidae, or green-fly; some of these may be generally found on our rose-bushes or on thistles, when they are much covered with Aphids; they are soft, maggot-like creatures with a great capacity for changing their shape and with much power of movement, especially of the anterior part of the body, which is stretched out and moved about to obtain and spear their prey: some of them are very transparent, so that the movements of the internal organs and their vivid colours can readily be seen: like so many other carnivorous Insects, their voracity appears to be insatiable. The larvae of many of the ordinary Hover-flies are of this kind. _Eristalis_ and its allies are totally different, they live in water saturated with filth, or with decaying vegetable matter (the writer has found many hundreds of the larvae of _Myiatropa florea_ in a pool of water standing in a hollow beech-tree). These rat-tailed maggots are of great interest, but as they have been described in almost every work on entomology, and as Professor Miall[422] has recently given an excellent account of their peculiarities, we need not now discuss them. Some of the flies of the genus _Eristalis_ are very like honey-bees, and appear in old times to have been confounded with them; indeed, Osten Sacken thinks this resemblance gave rise to the "Bugonia myth," a fable of very ancient origin to the effect that Honey-bees could be procured from filth, or even putrefying carcases, by the aid of certain proceedings that savoured slightly of witchcraft, and may therefore have increased the belief of the operator in the {500}possibility of a favourable result. It was certainly not bees that were produced from the carcases, but Osten Sacken suggests that _Eristalis_-flies may have been bred therein.

In the genus _Volucella_ we meet with a third kind of Syrphid larva. These larvae are pallid, broad and fleshy, surrounded by numerous angular, somewhat spinose, outgrowths of the body; and have behind a pair of combined stigmata, in the neighbourhood of which the outgrowths are somewhat larger; these larvae live in the nests of Bees and Wasps, in which they are abundant. Some of the _Volucella_, like many other Syrphidae, bear a considerable resemblance to Bees or Wasps, and this has given rise to a modern fable about them that appears to have no more legitimate basis of fact than the ancient Bees-born-of-carcases myth. It was formerly assumed that the _Volucella_-larvae lived on the larvae of the Bees, and that the parent flies were providentially endowed with a bee-like appearance that they might obtain entrance into the Bees' nests without being detected, and then carry out their nefarious intention of laying eggs that would hatch into larvae and subsequently destroy the larvae of the Bees. Some hard-hearted critic remarked that it was easy to understand that providence should display so great a solicitude for the welfare of the _Volucella_, but that it was difficult to comprehend how it could be, at the same time, so totally indifferent to the welfare of the Bees. More recently the tale has been revived and cited as an instance of the value of deceptive resemblance resulting from the action of natural selection, without reference to providence. There are, however, no facts to support any theory on the subject. Very little indeed is actually known as to the habits of _Volucella_ in either the larval or imaginal instars; but the little that is known tends to the view that the presence of the _Volucella_ in the nests is advantageous to both Fly and Bee. Nicolas has seen _Volucella zonaria_ enter the nest of a Wasp; it settled at a little distance and walked in without any fuss being made. Erné has watched the _Volucella_-larvae in the nests, and he thinks that they eat the waste or dejections of the larvae. The writer kept under observation _Volucella_-larvae and portions of the cells of _Bombus_, containing some larvae and pupae of the Bees and some honey, but the fly-larvae did not during some weeks touch any of the Bees or honey, and ultimately died, presumably of starvation. Subsequently, he experimented with _Volucella_-larvae and a portion {501}of the comb of wasps containing pupae, and again found that the flies did not attack the Hymenoptera; but on breaking a pupa of the Wasp in two, the fly-larvae attacked it immediately and eagerly; so that the evidence goes to show that the _Volucella_-larvae act as scavengers in the nests of the Hymenoptera. Künckel d'Herculais has published an elaborate work on the European _Volucella_; it is remarkable for the beauty of the plates illustrating the structure, anatomy and development, but throws little direct light on the natural history of the Insects. _V. bombylans_, one of the most abundant of our British species, appears in two forms, each of which has a considerable resemblance to a _Bombus_, and it has been supposed that each of the two forms is specially connected with the Bee it resembles, but there is no evidence to support this idea; indeed, there is some little evidence to the contrary. The genus _Merodon_ has larvae somewhat similar to those of _Volucella_, but they live in bulbs of _Narcissus_; _M. equestris_ has been the cause of much loss to the growers of Dutch bulbs; this Fly is interesting on account of its great variation in colour; it has been described as a whole series of distinct species.

The most remarkable of the numerous forms of Syrphid larvae are those of the genus _Microdon_ (Fig. 239), which live in ants' nests. They have no resemblance to Insect-larvae, and when first discovered were not only supposed to be little Molluscs, but were actually described as such under the generic names of _Parmula_ and _Scutelligera_. There is no appearance of segmentation of the body; the upper surface is covered by a sort of network formed by curved setae, which help to retain a coating of dirt; there is no trace externally of any head, but on the under surface there is a minute fold in which such mouth-organs as may be present are probably concealed; the sides of the body project so as to form a complex fringing arrangement; the terminal stigmata are very distinct, the lateral processes connected with them (the "Knospen" of Dr. Meijere), are, however, very irregular and placed at some distance from the stigmatic scar. Pupation occurs by the induration of the external covering and the growth from it, or rather through it, of two short horns in front. Inside this skin there is formed a soft pupa, of the kind usual in Cyclorrhaphous flies; the dehiscence of the external covering is, however, of unusual nature, three little pieces being {502}separated from the anterior part of the upper surface, while the lower face remains intact. The account of the pupation given by Elditt[423] is not complete: the two horns that project are, it would appear, not portions of the larval skin, but belong to the head of the pupa, and according to Elditt are used to effect the dehiscence of the case for the escape of the fly; there does not appear to be any head-vesicle. Nothing is known as to the details of the life of these anomalous larvae. M. Poujade has described two species found in France in the nests of the ant _Lasius niger_.[424] The larva we figure was found by Colonel Yerbury in nests of an _Atta_ in Portugal, and an almost identical larva was recently found by Mr. Budgett in Paraguay. The flies themselves are scarce, _Microdon mutabilis_ (formerly called _M. apiformis_) being one of the rarest of British flies. They have the antennae longer than is usual in Syrphidae, and the cross-veins at the outside of the wing are irregularly placed, so that the contour is very irregular: the resemblance to bees is very marked, and in some of the South American forms the hind legs are flattened and hairy like those of bees. The oviposition of _Microdon_ has been observed by Verhoeff;[425] he noticed that the fly was frequently driven away by the ants—in this case, _Formica sanguinea_—but returned undiscouraged to its task.

A brief résumé of the diverse modes of life of Syrphid larvae has been given by Perris,[426] and he also gives some information as to the curious horns of the pupae, but this latter point much {503}wants elucidation. Whether the Syrphidae, or some of them, possess a ptilinum that helps them to emerge from the pupa is more than doubtful, though its existence has been affirmed by several authors of good repute.[427]

SERIES 4. CYCLORRHAPHA SCHIZOPHORA

FAM. 33. MUSCIDAE ACALYPTRATAE.—This group of flies has been the least studied of all the Diptera; it is generally treated as composed of twenty or thirty different families distinguished by very slight characters. It is, however, generally admitted by systematists that these assemblages have not the value of the families of the other divisions of Diptera, and some even go so far as to say that they are altogether only equivalent to a single family. We do not therefore think it necessary to define each one _seriatim_; we shall merely mention their names, and allude to certain points of interest connected with them. Taken collectively they may be defined as very _small flies, with three-jointed antennae (frequently looking as if only two-jointed), bearing a bristle that is not terminally placed; frequently either destitute of squamae or having these imperfectly developed so as not to cover the halteres; and possessing a comparatively simple system of nervuration, the chief nervures being nearly straight, so that consequently few cells are formed_. These characters will distinguish the group {504}from all the other Diptera except from forms of Aschiza, and from certain Anthomyiidae, with both of which the Acalyptratae are really intimately connected. Considerable difference of opinion prevails as to the number of these divisions, but the families usually recognised are:—

1. Doryceridae.
2. Tetanoceridae.
3. Sciomyzidae.
4. Diopsidae.
5. Celyphidae.
6. Sepsidae incl. Piophilidae.
7. Chloropidae (= Oscinidae).
8. Ulidiidae.
9. Platystomidae.
10. Ephydridae.
11. Helomyzidae.
12. Dryomyzidae.
13. Borboridae.
14. Phycodromidae.
15. Thyreophoridae.
16. Scatophagidae. (= Scatomyzidae).
17. Geomyzidae incl. Opomyzidae.
18. Drosophilidae; incl. Asteidae.
19. Psilidae.
20. Tanypezidae (= Micropezidae).
21. Trypetidae.
22. Sapromyzidae incl. Lonchaeidae.
23. Rhopalomeridae.
24. Ortalidae.
25. Agromyzidae incl. Phytomyzidae.
26. Milichiidae.
27. Octhiphilidae.
28. Heteroneuridae.
29. Cordyluridae.

Brauer associates Conopidae with Acalyptrate Muscids, and calls the Group Holometopa; applying the term Schizometopa to the Calyptrate Muscidae.