Chapter VIII: Hemiptera, or Bugs—anoplura 532 (21)

No generalisation can yet be made as to the larvae of these divisions, neither can any characters be pointed out by which they can be distinguished from the larvae of the following families. In their habits they have nothing specially distinctive, and may be said to resemble the Anthomyiidae, vegetable matter being more used as food than animal; many of them mine in the leaves or stems of plants; in the genus _Dorycera_ the larva is aquatic, mining in the leaves of water-plants, and in Ephydridae several kinds of aquatic larvae are found, some of which are said to resemble the rat-tailed larvae of Syrphidae; certain of these larvae occur in prodigious quantities in lakes, and the Insects in some of their early stages serve the Mexicans as food, the eggs being called Ahuatle, the larvae Pusci, the pupae Koo-chah-bee. Some of the larvae of the Sciomyzidae are also aquatic: that of _Tetanocera ferruginea_ is said by Dufour to consist only of eight segments, and to be metapneustic; Brauer considers the Acalyptrate larvae to be, however, in general, amphipneustic, like those of Calyptratae. The Chloropidae are a very important family owing to their occasional excessive multiplication, and to their living on cereals and other grasses, various parts of which they attack, sometimes causing great losses to the agriculturist. The species of the genus _Chlorops_ are {505}famous for the curious habit of entering human habitations in great swarms: frequently many millions being found in a single apartment. Instances of this habit have been recorded both in France and England, Cambridge being perhaps the place where the phenomenon is most persistently exhibited. In the year 1831 an enormous swarm of _C. lineata_ was found in the Provost's Lodge at King's College and was recorded by Leonard Jenyns; in 1870 another swarm occurred in the same house if not in the same room.[428] Of late years such swarms have occurred in certain apartments in the Museums (which are not far from King's College), and always in the same apartments. No clue whatever can be obtained as to their origin; and the manner in which these flies are guided to a small area in numbers that must be seen to be believed, is most mysterious. These swarms always occur in the autumn, and it has been suggested that the individuals are seeking winter quarters.

Several members of the Acalyptratae have small wings or are wingless, as in some of our species of _Borborus_. The Diopsidae—none of which are European—have the sides of the head produced into long horns, at the extremity of which are placed the eyes and antennae; these curiosities (Fig. 240) are apparently common in both Hindostan and Africa. In the horned flies of the genus _Elaphomyia_, parts of the head are prolonged into horns of very diverse forms according to the species, but bearing on the whole a great resemblance to miniature stag-horns. A genus (_Giraffomyia_) with a long neck, and with partially segmented appendages, instead of horns on the head, has been recently discovered by Dr. Arthur Willey in New Britain. Equally remarkable are the species of _Celyphus_; they do not look like flies at all, owing to the scutellum being inflated and enlarged so as to cover all the posterior parts {506}of the body as in the Scutellerid Hemiptera: the wings are entirely concealed, and the abdomen is reduced to a plate, with its orifice beneath, not terminal; the surface of the body is highly polished and destitute of bristles. Whether this is a mimetic form, occurring in association with similar-looking Bugs is not known. The North American genus _Toxotrypana_ is furnished with a long ovipositor; and in this and in the shape of the body resembles the parasitic Hymenoptera. This genus was placed by Gerstaecker in Ortalidae, but is considered by later writers to be a member of the Trypetidae. This latter family is of considerable extent, and is remarkable amongst the Diptera for the way in which the wings of many of its members are ornamented by an elaborate system of spots or marks, varying according to the species.

FAM. 34. ANTHOMYIIDAE.—_Flies similar in appearance to the House-fly; the main vein posterior to the middle of the wing (4th longitudinal) continued straight to the margin, not turned upwards. Eyes of the male frequently large and contiguous, bristle of antenna either feathery or bare._ This very large family of flies is one of the most difficult and unattractive of the Order. Many of its members come close to the Acalyptrate Muscidae from which they are distinguished by the fact that a well-developed squama covers the halteres; others come quite as close to the Tachinidae, Muscidae and Sarcophagidae, but may readily be separated by the simple, not angulate, main vein of the wing. The larval habits are varied. Many attack vegetables, produce disintegration in them, thus facilitating decomposition. _Anthomyia brassicae_ is renowned amongst market gardeners on account of its destructive habits. _A. cana_, on the contrary, is beneficial by destroying the migratory Locust _Schistocerca peregrina_; and in North America, _A. angustifrons_ performs a similar office with _Caloptenus spretus_. One or two species have been found living in birds; in one case on the head of a species of _Spermophila_, in another case on a tumour of the wing of a Woodpecker. _Hylemyia strigosa_, a dung-frequenting species, has the peculiar habit of producing living larvae, one at a time; these larvae are so large that it would be supposed they are full grown, but this is not the case, they are really only in the first stage, an unusual amount of growth being accomplished in this stadium. _Spilogaster angelicae_, on the other hand, according to {507}Portschinsky, lays a small number of very large eggs, and the resulting larvae pass from the first to the third stage of development, omitting the second stage that is usual in Eumyiid Muscidae.[429]

FAM. 35. TACHINIDAE.—_First posterior cell of wing nearly or quite closed. Squamae large, covering the halteres: antennal arista bare: upper surface of body usually bristly._ This is an enormous family of flies, the larvae of which live parasitically in other living Insects, Lepidopterous larvae being especially haunted. Many have been reared from the Insects in which they live, but beyond this little is known of the life-histories, and still less of the structure of the larvae of the Tachinidae, although these Insects are of the very first importance in the economy of Nature. The eggs are usually deposited by the parent-flies near or on the head of the victim; Riley supposed that the fly buzzes about the victim and deposits an egg with rapidity, but a circumstantial account given by Weeks[430] discloses a very different process: the fly he watched sat on a leaf quietly facing a caterpillar of _Datana_ engaged in feeding at a distance of rather less than a quarter of an inch. "Seizing a moment when the head of the larva was likely to remain stationary, the fly stealthily and rapidly bent her abdomen downward and extended from the last segment what proved to be an ovipositor. This passed forward beneath her body and between the legs until it projected beyond and nearly on a level with the head of the fly and came in contact with the eye of the larva upon which an egg was deposited," making an addition to five already there. _Ugimyia sericariae_ does great {508}harm in Japan by attacking the silkworm, and in the case of this fly the eggs are believed to be introduced into the victim by being laid on mulberry leaves and swallowed with the food; several observers agree as to the eggs being laid on the leaves, but the fact that they are swallowed by the silkworm is not so certain. Sasaki has given an extremely interesting account of the development of this larva.[431] According to him, the young larva, after hatching in the alimentary canal, bores through it, and enters a nerve-ganglion, feeding there for about a week, after which the necessity for air becoming greater, as usual with larvae, the maggot leaves the nervous system and enters the tracheal system, boring into a tube near a stigmatic orifice of the silkworm, where it forms a chamber for itself by biting portions of the tissues and fastening them together with saliva. In this it completes its growth, feeding on the interior of the silkworm with its anterior part, and breathing through the stigmatic orifice of its host; after this it makes its exit and buries itself deeply in the ground, where it pupates. The work of rupturing the puparium by the use of the ptilinum is fully described by Sasaki, and also the fact that the fly mounts to the surface of the earth by the aid of this same peculiar air-bladder, which is alternately contracted and distended. Five, or more, of the _Ugimyia_-maggots may be found in one caterpillar, but only one of them reaches maturity, and emerges from the body. The Tachinid flies appear to waste a large proportion of their eggs by injudicious oviposition; but they make up for this by the wide circle of their victims, for a single species has been known to infest Insects of two or three different Orders.

The species of _Miltogramma_—of which there are many in Europe and two in England—live at the expense of Fossorial {509}Hymenoptera by a curious sort of indirect parasitism. They are obscure little flies, somewhat resembling the common House-fly, but they are adepts on the wing and have the art of ovipositing with extreme rapidity; they follow a Hymenopteron as it is carrying the prey to the nest for its young. When the wasp alights on the ground at the entrance to the nest, the _Miltogramma_ swoops down and rapidly deposits one or more eggs on the prey the wasp designs as food for its own young. Afterwards the larvae of the fly eat up the food, and in consequence of the greater rapidity of their growth, the young of the Hymenopteron perishes. Some of them are said to deposit living larvae, not eggs. Fabre has drawn a very interesting picture of the relations that exist between a species of _Miltogramma_ and a Fossorial Wasp of the genus _Bembex_[432]. We may remind the reader that this Hymenopteron has not the art of stinging its victims so as to keep them alive, and that it accordingly feeds its young by returning to the nest at proper intervals with a fresh supply of food, instead of provisioning the nest once and for all and then closing it. This Hymenopteron has a habit of catching the largest and most active flies—especially Tabanidae—for the benefit of its young, and it would therefore be supposed that it would be safe from the parasitism of a small and feeble fly. On the contrary, the _Miltogramma_ adapts its tactics to the special case, and is in fact aided in doing so by the wasp itself. As if knowing that the wasp will return to the carefully-closed nest, the _Miltogramma_ waits near it, and quietly selects the favourable moment, when the wasp is turning round to enter the nest backwards, and deposits eggs on the prey. It appears from Fabre's account that the _Bembex_ is well aware of the presence of the fly, and would seem to entertain a great dread of it, as if conscious that it is a formidable enemy; nevertheless the wasp never attacks the little fly, but allows it sooner or later to accomplish its purpose, and will, it appears, even continue to feed the fly-larvae, though they are the certain destroyers of its own young, thus repeating the relations between cuckoo and sparrow. Most of us think the wasp stupid, and find its relations to the fly incredible or contemptible. Fabre takes a contrary view, and looks on it as a superior Uncle Toby. We sympathise with the charming French naturalist, without forming an opinion.

{510}Doubtless there are many other interesting features to be found in the life-histories of Tachinidae, for in numbers they are legion. It is probable that we may have 200 species in Britain, and in other parts of the world they are even more abundant, about 1000 species being known in North America.[433] The family Actiidae is at present somewhat doubtful. According to Karsch,[434] it is a sub-family of Tachinidae; but the fourth longitudinal vein, it appears, is straight.

FAM. 36. DEXIIDAE.—_These Insects are distinguished from Tachinidae by the bristle of the antennae being pubescent, and the legs usually longer._ The larvae, so far as known, are found in various Insects, especially in Coleoptera, and have also been found in snails. There are eleven British genera, and about a score of species.

FAM. 37. SARCOPHAGIDAE.—_Distinguished from Muscidae and Tachinidae by little more than that the bristle of the antennae is feathery at the base but hair-like and very fine at the tip._—_Sarcophaga carnaria_ is one of the commonest British Insects; it is like the Blow-fly, though rather longer, conspicuously grey and black, with the thorax distinctly striped, and the pulvilli very conspicuous in the live fly. _Cynomyia mortuorum_ is a bright blue fly rather larger than the Blow-fly, of which it is a competitor; but in this country an unsuccessful one. The larvae of the two Insects are found together, and are said to be quite indistinguishable. _Cynomyia_ is said to lay only about half the number of eggs that the Blow-fly does, but it appears earlier in the year, and to this is attributed the fact that it is not altogether crowded out of existence by the more prolific _Calliphora_. The species of Sarcophagidae are usually viviparous, and one of them, _Sarcophila magnifica_ (_wohlfahrti_), has the habit of occasionally depositing its progeny in the nostrils of mammals, and even of human beings, causing horrible sufferings and occasionally death: it is said to be not uncommon in Europe but does not occur in Britain. The genus _Sarcophaga_ is numerous in species, and many of them are beneficial. Sir Sidney Saunders found in the Troad that Locusts were destroyed by the larvae of a _Sarcophaga_ living in their bodies; and {511}Künckel has recently observed that in Algeria several species of this genus attack Locusts and destroy large quantities by depositing living larvae in the Orthoptera. In North America the Army-worm is decimated by species of _Sarcophaga_.

Many of these Insects, when food is scarce, eat their own species with eagerness, and it seems probable that this habit is beneficial to the species. The parent-fly in such cases usually deposits more eggs than there is food for, thus ensuring that every portion of the food will be rapidly consumed, after which the partially-grown larvae complete their development by the aid of cannibalism. It is thus ensured that the food will raise up as many individuals as possible.

FAM. 38. MUSCIDAE.—_Bristle of antennae feathered._ This family contains many of the most abundant flies, including the House-fly, Blue-bottles or Blow-flies, Green-bottles, and other forms which, though very common, are perhaps not discriminated from one another by those who are not entomologists. The larvae live on carrion and decaying or excrementitious matters. The common House-fly, _Musca domestica_, runs through its life-history in a very short time. It lays about 150 very small eggs on dung or any kind of soft damp filth; the larvae hatch in a day or two and feed on the refuse; they may be full-grown in five or six days, and, then pupating, may in another week emerge as perfect flies. Hence it is no wonder that they increase to enormous numbers in favourable climates. They are thought to pass the winter chiefly in the pupal state. The House-fly is now very widely distributed over the world; it sometimes occurs in large numbers away from the dwellings of man. Of Blow-flies there are two common species in this country, _Calliphora erythrocephala_ and _C. vomitoria_. The Green-bottle flies, of which there are several species, belonging to the genus _Lucilia_, have the same habits as Blow-flies, though they do not commonly enter houses. The larvae are said to be indistinguishable from those of _Calliphora_.

The larvae of Eumyiid Muscidae are, when first hatched, metapneustic, but subsequently an anterior pair of stigmata appears, so that the larva becomes amphipneustic. They usually go through three stages, distinguished by the condition of the posterior stigmata. In the early instar these have a single heart-shaped fissure, in the second stage two fissures exist, {512}while in the third instar there is a greater diversity in the condition of the breathing apertures.

The various forms of Muscidae show considerable distinctions in the details of their natural history, and these in certain species vary according to the locality. This subject has been chiefly studied by Portschinsky, a Russian naturalist, and a very interesting summary of his results has been given by Osten Sacken,[435] to which the student interested in the subject will do well to refer.

A few years ago a great deal of damage was caused in the Netherlands by _Lucilia sericata_, a Green-bottle-fly, extremely similar to our common _L. caesar_, which deposited its eggs in great quantities on sheep amongst their wool. This epidemic was attributed to the importation of sheep from England; but, according to Karsch, there is reason to suppose that the fly was really introduced from Southern Europe or Asia Minor.[436]

The larvae of species of the genus _Lucilia_ sometimes attack man and animals in South America, but fortunately not in this country. The larva of _Lucilia_ (_Compsomyia_) _macellaria_ is called the screw-worm, and is the best known of the forms that infest man, the larvae living in the nasal fossae and frontal sinuses, and causing great suffering. The fly is common in North America, but is said never to attack man farther north than in Kansas. A little fly (_Stomoxys calcitrans_), very like the common house-fly though rather more distinctly spotted with grey and black, and with a fine, hard, exserted proboscis, frequently enters our houses and inflicts a bite or prick on us. It is commonly mistaken for an ill-natured house-fly that has taken to biting. It is frequently a source of irritation to cattle. A closely allied fly, _Haematobia serrata_, is very injurious to cattle in North America, but the same species causes no serious annoyance in England. We may mention that the various attacks of Dipterous larvae on man have received the general name "myiasis."

The Tse-tse fly (_Glossina morsitans_), another ally of _Stomoxys_, is not very dissimilar in size and shape to the blow-fly.[437] {513}It bites man and animals in South Africa, and if it have previously bitten an animal whose blood was charged with the Haematozoa that really constitute the disease called Nagana (fly-disease), it inoculates the healthy animal with the disease; fortunately only some species are susceptible, and man is not amongst them. It has recently been shown by Surgeon Bruce[438] that this fly multiplies by producing, one at a time, a full-grown larva, which immediately changes to a pupa, as do the members of the series Pupipara. There are already known other Muscid flies with peculiarities in their modes of reproduction, so that it is far from impossible that the various conditions between ordinary egg-laying and full-grown larva- or pupa-production may be found to exist. Although it has been supposed that the Tse-tse fly is a formidable obstacle to the occupation of Africa by civilised men, there is reason to suppose that this will not ultimately prove to be the case. It only produces disease when this pre-exists in animals in the neighbourhood; only certain species are liable to it; and there is some evidence to the effect that even these may in the course of a succession of generations become capable of resisting the disease inoculated by the fly. As long ago as 1878 Dr. Drysdale suggested[439] that this fly only produces disease by inoculating a blood-parasite, and all the evidence that has since been received tends to show that his idea is correct.

Although the facts we have mentioned above would lead to the supposition that Muscidae are unmitigated nuisances, yet it is probable that such an idea is the reverse of the truth, and that on the whole their operations are beneficial. It would be difficult to overestimate their value as scavengers. And in addition to this they destroy injurious creatures. Thus in Algeria _Idia fasciata_, a fly like the House-fly, destroys the {514}dreaded migratory Locust _Schistocerca peregrina_ in great quantities, by the larvae eating the eggs of the Locust. The female of this fly, in order to reach the desired food, penetrates from one to three inches below the surface of the ground.

FAM. 39. OESTRIDAE (_Bot-flies_).—_Rather large or very large flies, with extremely short antennae, bearing a segmented arista, the front of the head prominent, the posterior part of the wings frequently rough, and with but few veins: the mouth usually atrophied, the trophi being represented only by tubercles; larvae living in Vertebrates, usually Mammals, though it is possible that a few occur in Birds and even in Reptiles._ This is a family of small extent, less than 100 species being known from all the world, yet it is of much interest on account of the habits of its members, which, though of large size, live entirely at the expense of living Vertebrates, to the viscera or other structures of which they have definite relations, varying according to the species. Some (_Gastrophilus_, etc.) live in the alimentary canal; others (_Hypoderma_, etc.) are encysted in or under the skin; while others (_Oestrus_, etc.) occupy the respiratory passages. As many of them attack the animals used by man, and some of them do not spare man himself, they have attracted much attention, and there is an extensive literature connected with them; nevertheless the life-histories are still very incompletely known. Indeed, the group is from all points of view a most difficult one, it being almost impossible to define the family owing to the great differences that exist in important points. Some think the family will ultimately be dismembered; and Girschner has recently proposed to treat it as a division of Tachinidae. The chief authority is Brauer, in whose writings the student will find nearly all that is known about Oestridae.[440] Some of them exist in considerable numbers (it is believed that they are now not so common as formerly), and yet the flies are but rarely met with, their habits being in many respects peculiar. Some of them, for purposes of repose, frequent the summits of mountains, or towers, or lofty trees. Some have great powers of humming; none of them are known to bite their victims, indeed the atrophied mouth of most of the Oestridae forbids such a proceeding.

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Some deposit their eggs on the hairs of the beasts from which the larvae are to draw their nutriment, but others place their larvae, already hatched, in the entrances of the nasal passages. They do not feed on the blood or tissues of their victims, but on the secretions, and these are generally altered or increased by the irritation induced by the presence of the unwelcome guests. It would appear, on the whole, that their presence is less injurious than would be expected, and as they always quit the bodies of their hosts for the purposes of pupation, a natural end is put to their attacks. We have ten species in Britain, the animals attacked being the ox, the horse, the ass, the sheep, and the red deer; others occasionally occur in connexion with animals in menageries. The eggs of _Gastrophilus equi_ are placed by the fly, when on the wing, on the hair of horses near the front parts of the body, frequently near the knee, and, after hatching, the young larvae pass into the stomach of the horse either by being licked off, or by their own locomotion; in the stomach they become hooked to the walls, and after being full grown pass out with the excreta: the Bots—as these larvae are called—are sometimes very numerous in the stomach, for a fly will lay as many as four or five hundred eggs on a single horse: in the case of weakly animals, perforation of the stomach has been known to occur in consequence of the habit of the Bot of burying itself to a greater or less extent in the walls of the stomach. _Hypoderma bovis_ and _H. lineata_ attack the ox, and the larvae cause tumours in the skin along the middle part of the back. It was formerly {516}inferred from this that the fly places its eggs in this situation, and as the cattle are known to dread and flee from the fly, it was supposed to be on account of the pain inflicted when the egg was thrust through the skin. Recent observations have shown that these views are erroneous, but much still remains to be ascertained. The details of oviposition are not yet fully known, but it appears that the eggs are laid on the lower parts of the body, especially near the heels, and that they hatch very speedily.[441] As the imago of _Hypoderma_ appears for only a very short period in the summer, the time of the oviposition is certain. The newly-disclosed larva is considerably different from the more advanced instar found in the skin of the back; moreover, a long period of many months intervenes between the hatching of the larva and its appearance in the part mentioned. Brauer has shown that when the grub is first found in that situation it is entirely subcutaneous. Hence it would be inferred that the newly-hatched larva penetrated the skin probably near the spot it was deposited on, and passed a period in subcutaneous wandering, on the whole going upwards till it arrived at the uppermost part: that after moulting, and in consequence of greater need for air, it then pierced the skin, and brought its breathing organs into contact with the external air; that the irritation caused by the admission of air induced a purulent secretion, and caused the larva to be enclosed in a capsule. Dr. Cooper Curtice has however found, in the oesophagus of cattle, larvae that he considers to be quite the same as those known to be the young of _Hypoderma_; and if this prove to be correct, his inference that the young larvae are licked up by the cattle and taken into the mouth becomes probable. The larva, according to this view, subsequently pierces the oesophagus and becomes subcutaneous by passing through the intervening tissues. The later history of the grub is briefly, that when full grown it somewhat enlarges the external orifice of its cyst, and by contractions and expansions of the body, passes to the surface, falls to the ground, buries itself and becomes a pupa. If Dr. Curtice be correct, there should, of course, be as many, if not more, larvae found in the oesophagus as in the back of the animal; but, so far as is known, this is not the case, and we shall not be surprised if the normal course of development be found different from what Dr. Curtice supposes it to be. His {517}observations relate to _Hypoderma lineata_. Our common British species is usually supposed to be _H. bovis_; but from recent observations it seems probable that most of the "Ox-warbles" of this country are really due to the larvae of _H. lineata_.

The history of _Oestrus ovis_, which attacks the sheep, is also incompletely known, but appears to be much simpler. This fly is viviparous, and deposits its young larvae at the entrance of the nasal passages of the sheep, thereby causing extreme annoyance to the animal. The larvae penetrate to the frontal sinuses to complete their growth. The duration of their lives is unknown, for it is commonly the case that larvae of various sizes are found together. _Cephenomyia rufibarbis_ has recently been found in Scotland. It attacks the Red deer, and its life-history is similar to that of _Oestrus ovis_, though the larvae apparently prefer to attain their full growth in the pharynx of the deer.

In reference to the Oestridae that attack man, we may merely mention that the larva of the _Hypoderma_ of the ox is occasionally found in Europe infesting human beings, but only as an extremely rare and exceptional event; and that only those engaged in attending on cattle are attacked; from which it is inferred that the flies are deceived by an odour emanating from the garments. In America numerous cases are known of Oestrid larvae being taken from the body of man, but information about them is very scanty. It appears, however, that there are at least four species, one of which, _Dermatobia noxialis_, is known as a fly as well as a larva. Whether any of these are peculiar to man is uncertain.[442] There are several larvae of Muscidae that have similar habits to the Oestridae; hence the statements that exist as to larvae being found in birds and reptiles cannot be considered to apply to members of the latter family until the larvae have been studied by an expert.

The family Ctenostylidae has been established by Bigot for a South American Insect, of which only a single individual exists in collections. It is doubtful whether it can be referred to Oestridae.[443]

SERIES V. PUPIPARA

The four families included in this Series are, with the exception of the Hippoboscidae, very little known. Most of {518}them live by sucking blood from Mammals and Birds, and sometimes they are wingless parasites. The single member of the family Braulidae lives on bees. The term Pupipara is erroneous, and it would be better to revert to Réaumur's prior appellation Nymphipara. Müggenburg has suggested that the division is not a natural one, the points of resemblance that exist between its members being probably the results of convergence. Recent discoveries as to the modes of bringing forth of Muscidae give additional force to this suggestion. A satisfactory definition of the group in its present extent seems impossible.

FAM. 40. HIPPOBOSCIDAE.—_Wings very variable, sometimes present and large, then with waved surface and thick nervures confined to the anterior and basal part; sometimes mere strips, sometimes entirely absent._ Certain members of this family are well known, the Forest-fly, or Horse-fly, and the Sheep-tick belonging to it. The proboscis is of peculiar formation, and not like that of other flies. Seen externally it consists of two elongate, closely adapted, hard flaps; these are capable of diverging laterally to allow an inner tube to be exserted from the head. The details and morphology of the structure have recently been discussed by Müggenburg.[444] _Melophagus ovinus_, commonly called the Sheep-tick, is formed for creeping about on the skin of the sheep beneath the wool, and may consequently be procured with ease at the period of sheep-shearing: it has no resemblance to a fly, and it is difficult to persuade the uninitiated that it is such. _Hippobosca equina_ (called in this country the Forest-fly, perhaps because it is better known in the New Forest than elsewhere), looks like a fly, but will be readily recognised by the two little cavities on the head, one close to each eye, in which the antennae are concealed, only the fine bristle projecting. Very little seems to be known as to the Natural History of this fly. _Lipoptena cervi_ lives on the Red deer; the perfect Insect has apparently a long life, and both sexes may be found in a wingless state on the deer all through the winter. When first disclosed in the summer they are however provided with wings, but when they have found a suitable host they bite off, or cast, the wings. The female, it appears, does this more promptly than the male, so that it is difficult to get winged individuals of the former sex.[445]

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Most of the known Hippoboscidae live on birds, and are apparently specially fond of the Swallow tribe. They are all winged, though in some species the wings are very small. The bird-infesting Hippoboscidae have been very little studied, and will probably form a distinct family; the antennae of _Stenopteryx hirundinis_ are quite different from those of _Hippobosca_. The development is remarkable, and has been studied by Leuckart[446] and by Pratt[447] in the case of _Melophagus ovinus_. The ovaries are peculiarly formed, and produce one large egg at a time; this passes into the dilated oviduct, and there goes through its full growth and a certain amount of development; it is then extruded, and undergoing little or no change of form becomes externally hardened by the excretion of chitin, passing thus into the condition of the Eumyiid pupa. Dufour thought that there is no larval stage in this Insect, but it is quite clear from later researches that he was wrong, and that a larval stage of a peculiar kind, but in some respects resembling that of the Eumyiid Muscidae, occurs. The larva has no true head, but the anterior part of the body is invaginated, and the most anterior part again protrudes in the invagination, so that two little passages appear on section (Fig. 246); the upper one leads to the stomach, which is of very large size. The tracheal system is peculiar; it is metapneustic, there being neither anterior nor lateral spiracles. Pratt says that there is at first a single pair of terminal spiracles, and subsequently three pairs, hence he considers that the terminal part of the body corresponds to three segments. This is however probably a mistaken view; it appears more probable that the so-called three pairs of stigmata really correspond with the complex {520}condition of the stigmata in the later instars of certain other Dipterous larvae. The _Melophagus_-larva is nourished by secretion from certain glands of the mother-fly; this is swallowed and the stomach is greatly distended by this milky fluid. Probably it was this condition that induced Dufour to suppose the larva to be only an embryo.

Some of the Hippoboscidae that live on birds take to the wing with great readiness, and it is probable that these bird-parasites will prove more numerous than is at present suspected.

We may here notice an animal recently described by Dr. Adensamer and called _Ascodipteron_.[448] He treats it as the female imago of a Pupiparous Dipteron. It was found buried in the skin of the wing of a bat of the genus _Phyllorhina_, in the Dutch East Indies, only one individual being known. It is entirely unsegmented, and externally without head. If Dr. Adensamer should prove to be correct in his surmise the creature can scarcely be inferior in interest to the Strepsiptera.

FAM. 41. BRAULIDAE.—This consists only of a minute Insect that lives on bees. The antennae are somewhat like those of the sheep-tick, though they are not so completely concealed in the cavities in which they are inserted. According to Müggenburg[449] a ptilinum exists, and he is also of opinion that although the parts of the mouth differ very much from those of Hippoboscidae they are essentially similar. Lucas says that _Braula_ specially affects the thorax of the bee: Müggenburg, that it is fond of the queen-bee because of the exposed membranes between the body-segments that exist in that sex. Whether this Insect is truly Pupiparous is unknown, though Boise states that a pupa is deposited in the cell of the bee by the side of the young larva of {521}the bee, and appears as the perfect Insect in about twenty-one days. Müggenburg suggests that _Braula_ may be oviparous, as he has never found a larva in the abdomen. Packard says that on the day the larva hatches from the egg it sheds its skin and turns to an oval puparium of a dark brown colour. The Insect is frequently though inappropriately called bee-louse; notwithstanding its name it is not quite blind, though the eyes are very imperfect.

FAM. 42. STREBLIDAE.— _Winged; possessing halteres; the head small, narrow and free._ These very rare Diptera are altogether problematic. According to Kolenati the larvae live in bats' excrement and the perfect Insects on the bats.[450] If the former statement be correct the Insects can scarcely prove to be Pupipara. The wing-nervuration is, in the figures of the Russian author, quite different from that of Hippoboscidae. The Streblidae have been associated by some entomologists with Nycteribiidae, and by Williston with Hippoboscidae.

FAMILY 43. NYCTERIBIIDAE.—The species of this family are found on bats; they are apparently rare, and we have been able to examine only one species. The form is very peculiar, the {522}Insects looking as if the upper were the under surface. They are wingless, with a narrow head, which reposes on the back of the thorax. The prothorax appears to be seated on the dorsum of the mesothorax. According to Müggenburg there is no trace of a ptilinum. A brief note on the metamorphosis[451] by Baron Osten Sacken indicates that the mature larva differs from that of _Melophagus_ in the arrangement of the stigmata; they appear to be dorsal instead of terminal. There are apparently no characters of sufficient importance to justify the association of these Insects with the other divisions of Pupipara; the sole ground for this connection being the supposed nature of the life-history of the larva.

SUB-ORDER APHANIPTERA or SIPHONAPTERA (_Fleas_)

FAM. PULICIDAE.—_Wingless, with the body laterally compressed, so that the transverse diameter is small, the vertical one great. The head indistinctly separated from the body, small, with short thick antennae placed in depressions somewhat behind and above the unfaceted eyes. These are always minute, and sometimes wanting._

{523}

We all know that the Flea is so flat, or compressed sideways, that it does not mind the most severe squeeze. This condition is almost peculiar to it; a great flattening of the body is common in Insects—as is seen in another annoying Insect, the bed-bug—but the compression, in the flea, is in the reverse direction. In other respects the external anatomy of the flea shows several peculiarities, the morphological import of which has not yet been elucidated. The head is of very peculiar shape, small, with the antennae placed in an unusual position; the clypeus is said to be entirely absent, the front legs are articulated in such a manner that they have a large additional basal piece—called by some anatomists the ischium—and in consequence appear to be placed far forwards, looking as if they were attached to the head; the meso- and meta-thorax have certain flaps that have been considered to be homologues of wings; and the maxillary palpi are attached to the head in such a way that they appear to play the part of the antennae of other Insects (Fig. 250), and were actually considered to be the antennae by Linnaeus, as well as others; the mouth-parts themselves are differently constructed from those of any other Insects.[452] The maxillae and labium are considered to be not only present, but well developed, the former possessing palpi moderately well developed, while the labial palps are very large and of highly peculiar form, being imperfectly transversely jointed and acting as sheaths; the mandibles are present in the form of a pair of elongate, slender organs, with serrated edges; and there is an unpaired, elongate pricking-organ, thought by some to be a hypopharynx, and by others a labrum.

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The antennae are of unusual form, consisting of two basal joints, and, loosely connected therewith, a terminal mass of diverse form and more or less distinctly, though irregularly, segmented. The full number of ten stigmata exists, Wagner giving three thoracic, with seven abdominal, placed on segments 2-8 of the abdomen; but Packard thinks the supposed metathoracic stigma is really the first abdominal. Fleas undergo a very complete metamorphosis; the larvae are wormlike, resembling those of Mycetophilid Diptera (Fig. 252). The egg of the cat's flea is deposited among the fur of the animal, but (unlike the eggs of other parasites) apparently is not fastened to the hair, for the eggs fall freely to the ground from infested animals; the young larva when hatched bears on the head a curious structure for breaking the egg-shell. It has the mouth-parts of a mandibulate Insect and is peripneustic, having ten pairs of stigmata. It subsequently becomes of less elongate form. Flea-larvae are able to nourish themselves on almost any kind of refuse animal matter, Laboulbène having reared them on the sweepings of apartments; they may perhaps sometimes feed on blood; at any rate the contents of the alimentary canal appear red through the transparent integuments. When full grown the larva makes a cocoon, and frequently covers it with pieces of dust. The perfect flea appears in a week or two thereafter; the pupa has the members free. The food of the larvae of fleas has been much discussed and a variety of statements made on the subject. It has been stated that the mother-flea after being gorged with blood carries some of it to the young, but Künckel has shown that there is very little foundation for this tale. Enormous numbers of fleas are sometimes found in uninhabited apartments to which animals have previously had access, and these fleas will attack in numbers and with great eagerness any unfortunate person who may enter {525}the apartment. The cat-flea can pass through its growth and metamorphosis with excessive rapidity, the entire development of a generation in favourable conditions extending but little beyond a fortnight.[453]

About a hundred kinds of fleas are known, all of which live on mammals or birds. _Hystrichopsylla talpae_ (Fig. 250) is one of the largest, it occurs on the Mole. It was found by Ritsema in the nests of _Bombus subterraneus_ (and was described under the name of _Pulex obtusiceps_). As these nests are known to be harried by Voles, and as this flea has also been found on Field-mice, it is probable that the parasites are carried to the nests by the Voles. The species that chiefly infests man is _Pulex irritans_, an Insect that is nearly cosmopolitan, though arid desert regions are apparently unsuitable to it. _Pulex avium_ occurs on a great variety of birds. _P. serraticeps_ infests the dog and the cat, as well as a variety of other Mammals. It is a common opinion that each species of Mammal has its own peculiar flea, but this is far from correct. Fleas pass readily from one species of animal to another; the writer formerly possessed a cat that was a most determined and successful hunter of rabbits, and she frequently returned from her excursions swarming with fleas that she had become infested with when in the rabbits' burrows; her ears were on some occasions very sore from the flea-bites. Some of the fleas of other animals undoubtedly bite man. There appears, however, to be much difference in the liability of different individuals of our own species to the bites of fleas. _Sarcopsylla penetrans_ differs in habits from other fleas, as the female buries the anterior parts of her body in the flesh of man or other Vertebrates, and the abdomen then becomes enormously enlarged and distended and undergoes a series of changes that are of much interest.[454] While in this position the Insect discharges a number of eggs. This species multiplies sufficiently to become a serious pest in certain regions, the body of one man having been known to be affording hospitality to 300 of these fleas. _Sarcopsylla penetrans_ is known as the Sand-flea, or chigger, and by numerous other names. Originally a native of tropical America it has been carried to other parts of the world. Another _Sarcopsylla_, _S. gallinacea_, attaches itself to the eyelids {526}of the domestic fowl in Ceylon, and an allied form, _Rhynchopsylla pulex_, fastens itself to the eyelids and other parts of the body of birds and bats in South America. In Turkestan _Vermipsylla alakurt_ attacks cattle—ox, horse, camel, sheep—fastening itself to the body of the animal after the fashion of a tick. Retaining this position all through the winter, it becomes distended somewhat after the manner of the Sand-flea, though it never forms a spherical body. The parts of the mouth in this Insect (Fig. 251) are unusually long, correlative with the thickness of the skins of the animals on which it lives. Grassi considers that the dog's flea, _Pulex serraticeps_, acts as the intermediate host of Taenia.

Great difference of opinion has for long prevailed as to whether fleas should be treated as a Sub-Order of Diptera or as a separate Order of Insects. Wagner and Künckel, who have recently discussed the question, think they may pass as aberrant Diptera, while Packard,[455] the last writer on the subject, prefers to consider them a separate Order more closely allied to Diptera than to any other Insects. Although widely known as Aphaniptera, several writers call them Siphonaptera, because Latreille proposed that name for them some years before Kirby called them Aphaniptera. Meinert considers them a separate Order and calls it Suctoria, a most unfortunate name.

ORDER VIII. THYSANOPTERA.

_Small Insects, with a palpigerous mouth placed on the under side of the
head and apposed to the sternum so as to be concealed. With four slender
wings, fringed with long hairs on one or both margins, or with rudiments
of wings, or entirely apterous. Tarsi of one or two joints, terminated by
a vesicular structure. The young resemble the adult in general form, but
there is a pupal stadium in which the Insect is quiescent and takes no
food._

The tiny Insects called Thrips are extremely abundant and may often be found in profusion in flowers. Their size is only from 1/50 to ⅓ of an inch in length; those of the latter magnitude are in fact giant species, and so far as we know at present are found only in Australia (Fig. 253). As regards the extent {527}of the Order it would appear that Thysanoptera are insignificant, as less than 150 species are known. Thrips have been, however, very much neglected by entomologists, so it will not be a matter for surprise if there should prove to be several thousand species. These Insects present several points of interest; their mouth-organs are unique in structure; besides this, they exhibit so many points of dissimilarity from other Insects that it is impossible to treat them as subdivisions of any other Order. They have, however, been considered by some to be aberrant Pseudoneuroptera (cf. Vol. V.), while others have associated them with Hemiptera. Both Brauer and Packard have treated Thysanoptera as a separate Order, and there can be no doubt that this is correct. Thysanoptera have recently been monographed by Uzel in a work that is, unfortunately for most of us, in the Bohemian language.[456]

The antennae are never very long, and are 6 to 9-jointed. The head varies much, being sometimes elongate and tubular, but sometimes short; it has, however, always the peculiarity that the antennae are placed quite on its front part, and that the mouth appears to be absent, owing to its parts being thrust against the under side of the thorax and concealed. Their most remarkable peculiarity is that some of them are asymmetrical: Uzel looks on the peculiar structure, the "Mundstachel," _m_, _m_ {528}(Fig. 254) found on the left side of the body, as probably an enormous development of the epipharynx. Previous to the appearance of Uzel's work, Garman had, however, correctly described the structure of the mouth;[457] he puts a different interpretation on the parts; he points out that the mandibles (_j_), so-called by Uzel, are attached to the maxillae, and he considers that they are really jointed, and that they are lobes thereof; while the Mundstachel or piercer is, he considers, the left mandible; the corresponding structure of the other side being nearly entirely absent. He points out that the labrum and endocranium are also asymmetrical. We think Garman's view a reasonable one, and may remark that dissimilarity of the mandibles of the two sides is usual in Insects, and that the mandibles may be hollow for sucking, as is shown by the larvae of Hemerobiides. There are usually three ocelli, but they are absent in the entirely apterous forms.

The wings appear to spring from the dorsal surface of the body, not from the sides; the anterior pair is always quite separated from the posterior; the wings are always slender, sometimes very slender; in other respects they exhibit considerable variety; sometimes the front pair are different in colour and consistence from the other pair. The abdomen has ten segments, the last of which is often tubular in form. The peculiar vesicular structures by which the feet are terminated are, during movement, alternately distended and emptied, and have two hooks or claws on the sides. The stigmata are extremely peculiar, there being four pairs, the first being the mesothoracic, 2nd {529}metathoracic, 3rd on the second abdominal segment, 4th on the eighth abdominal segment.[458] There are four Malpighian tubes, and two or three pairs of salivary glands. The dorsal vessel is said to be a short sack placed in the 7th and 8th abdominal segments. The abdominal ganglia of the ventral chain are concentrated in a single mass, placed in, or close to, the thorax; the thorax has two other approximated ganglia, as well as an anterior one that appears to be the infra-oesophageal.

The metamorphosis is also peculiar; the larva does not differ greatly in appearance from the adult, and has similar mouth-organs and food-habits. The wings are developed outside the body at the sides, and appear first, according to Heeger, after the third moult. The nymph-condition is like that of a pupa inasmuch as no nourishment is taken, and the parts of the body are enclosed in a skin: in some species there is power of movement to a slight degree, but other species are quite motionless. In some cases the body is entirely bright red, though subsequently there is no trace of this colour. Jordan distinguishes two nymphal periods, the first of which he calls the pronymphal; in it the Insect appears to be in a condition intermediate between that of the larva and that of the true nymph; the old cuticle being retained, though the hypodermis is detached from it and forms a fresh cuticle beneath it. This condition, as Jordan remarks, seems parallel to that of the male Coccid, and approaches closely to complete metamorphosis; indeed the only characters by which the two can be distinguished appear to be (1) that the young has not a special form; (2) that the wings are developed outside the body.

Thrips take their food, it is believed, in the same manner as Aphidae, by suction; but the details of the process are not by any means certain, and examination of the stomach is said to have resulted in finding pollen therein. Walsh thought that Thysanoptera pierce and suck Aphidae. An elaborate inquiry by Osborn[459] failed to elicit satisfactory confirmation of Walsh's idea, though Riley and Pergande support it to some extent; Osborn concludes that the ordinary food is not drawn directly from sap, but consists of exudation or pollen, the tissues {530}of the plant being pierced only when a supply of food from the usual sources falls short. Members of this family have been reputed as being very injurious to cultivated plants, especially to cereals, and it is said that as a result the harvests in Europe have been seriously diminished. Several species may take part in the attacks. These appear to be directed chiefly against the inflorescence. Lindeman thought that _Limothrips denticornis_ (= _Thrips secalina_), and _Anthothrips aculeata_ (= _Phloeothrips frumentarius_), were the most destructive species in an attack of Thrips on corn that he investigated in Russia. Uzel suggests that injuries due to other causes are sometimes ascribed to Thrips.[460] In hot-houses these Insects are well known, and sometimes occasion considerable damage to foliage. The German horticulturalists call them black-fly, in distinction from Aphidae or green-fly. Some Thysanoptera live under bark, and even in fungi, and in Australia they form galls on the leaves of trees. This observation is due to Mr Froggatt, and is confirmed by specimens he sent to the writer. Vesicular bodies in the leaves of _Acacia saligna_ were traversed on one side by a longitudinal slit, and on a section being made, nothing but Thrips, in various stages of growth, was found inside them. A second kind of gall, forming masses of considerable size on the twigs of _Callistemon_, is said by Mr Froggatt to be also due to Thrips, as is a third kind on _Bursaria spinosa_. It is curious that Thrips' galls have not been observed in other parts of the world.

Thysanoptera are devoured by small bugs of the genus _Triphleps_, as well as by beetles; a small Acarid attacks them by fixing itself to the body of the Thrips. Nematode worms and their eggs were found by Uzel in the body-cavity. He found no less than 200 Nematodes in one Thrips, and noticed that they had entirely destroyed the ovaries. Woodpeckers, according to him, tear off the bark of trees and eat the Thysanoptera that are concealed thereunder, though one would have surmised that these minute Insects are too small to be game for such birds. They have, it appears, no special protection, except that one species (a larva of _Phloeothrips_ sp.) is said to emit a protective fluid.