Chapter VIII: Hemiptera, or Bugs—anoplura 532 (19)

It forms no part of our task to deal with general subjects, but we may be pardoned for calling attention to the bearing the metamorphosis of the higher Diptera has on our ideas of heredity in Insects. The fly bears no resemblance whatever to the larva, and is only obtained by the organic destruction of the latter, which occurs before the perfection of the sexual organs takes place, and yet the fly reproduces itself only secondarily, but primarily gives rise to the totally different larva. It is supposed that the larval structures have been gradually acquired, and yet they are transmitted with the utmost faithfulness by the totally different fly. We can only conclude that that which is bequeathed in each species is the early state of a particular process of development from which the subsequent stages follow necessarily if the developing organism be placed in conditions having on it influences like to those that influenced the ancestors.

CLASSIFICATION.—The classification of Diptera is as yet very imperfect. Formerly they were divided into two great groups, Nemocera and Brachycera, according to the structure of the antennae, as previously mentioned. This division has been abandoned, and the term Brachycera is now applied to only a small part of the old section that bore the name. The primary division usually adopted at present is into Orthorrhapha and Cyclorrhapha. The characters of these two groups are based on the nature of the metamorphosis, and have been gradually elaborated by Brauer in various memoirs.[362] The Orthorrhapha includes the forms with obtected pupae, the Cyclorrhapha those with a nymph-compound, as previously described. This distinction is of great importance, but unfortunately it is difficult to apply to the fly itself; the only character that can be used in {455}connection with the imago is the existence of a suture over the insertion of the antennae in a portion, but not all, of the Cyclorrhapha.[363] The next set of divisions used by Brauer divides the Order into four sections, viz. 1. Orthorrhapha Nematocera, 2. O. Brachycera, 3. Cyclorrhapha Aschiza, 4. C. Schizophora. As these four groups are recognised more readily than the two major groups the student will do well at first to disregard the primary division and consider the Diptera as divisible into four great groups. To these four divisions we, however, add temporarily a fifth, viz. Pupipara. This is included by Brauer in Schizophora, but it appears to be really an unnatural complex, and had better be kept separate till it has been entirely reconsidered. These great sections may be thus summarised:—

Series 1. _Orthorrhapha Nemocera._—Antennae with more than 6 segments,
not terminated by an arista; with the segments of the flagellum more or
less similar to one another. Palpi slender and flexible, four- or
five-jointed.[364]

Series 2. _Orthorrhapha Brachycera._—Antennae variable, but never truly
Nemocerous nor like those of Cyclorrhapha; when an arista is present it
is usually placed terminally, not superiorly; when an arista is not
present the flagellum terminates as an appendage consisting of a variable
number of indistinctly separated segments; thus the flagellum is not
composed of similar joints; [rarely are the antennae as many as
seven-jointed]. Palpi only one- or two-jointed.[365] Around the insertion
of the antennae there is no definite arched suture enclosing a small
depressed space. The nervuration of the wings is usually more complex
than in any of the other divisions.

Series 3. _Cyclorrhapha Aschiza._—Antennae composed of not more than
three joints and an arista; the latter is not terminal. Front of head
without definite arched suture over the antennae, but frequently with a
minute area of different colour or texture there. This group consists of
the great family Syrphidae, and of four small families, viz. Conopidae,
Pipunculidae, Phoridae, and Platypezidae. The section is supposed to be
justified by its being Cyclorrhaphous in pupation, and by the members not
possessing a ptilinum (or having no trace of one when quite mature). The
Syrphidae are doubtless {456}a natural group, but the association with
them of the other families mentioned is a mere temporary device. The
greatest difficulty is experienced in deciding on a position for
Phoridae, as to which scarcely any two authorities are agreed.

Series 4. _Cyclorrhapha Schizophora_, or Eumyiid flies. The antennae
consist of three joints and an arista. In the Calyptratae the frontal
suture, or fold over the antennae, is well marked and extends downwards
along each side of the face, leaving a distinct lunule over the antennae.
In the Acalyptrate Muscids the form of the head and of the antennae vary
much and are less characteristic, but the wings differ from those of
Brachycera by their much less complex nervuration.

Series 5. _Pupipara._ These are flies of abnormal habits, and only found
in connection with living Vertebrates, of which they suck the blood (one
species, _Braula caeca_, lives on bees). Many are wingless, or have wings
reduced in size. The young are produced alive, full grown, but having
still to undergo a metamorphosis. This group consists of a small number
of flies of which some are amongst the most aberrant known. This is
specially the case with the Nycteribiidae. This Section will probably be
greatly modified, as it is far from being a natural assemblage.[366]

The Sub-Order _Aphaniptera_, or Fleas, considered a distinct Order by
many entomologists, may for the present be placed as a part of Diptera.

It must be admitted that these sections are far from satisfactory. Brauer divides them into Tribes, based on the nature of the larvae, but these tribes are even more unsatisfactory than the sections, hosts of species being entirely unknown in the larval state, and many of those that are known having been very inadequately studied. We must admit that the classification of Diptera has at present advanced but little beyond the stage of arranging them in natural families capable of exact definition. We may, however, draw attention to the attempt that is being made by Osten Sacken to remodel the classification of the Nemocera and Brachycera by the combination of families into super-families.[367] He proposes to divide the Nemocera into two super-families: 1. Nemocera Vera, including all the families from Cecidomyiidae to Tipulidae; 2. Nemocera Anomala, consisting of the small families Bibionidae, Simuliidae, Blepharoceridae, Rhyphidae and Orphnephilidae.

For Orthorrhapha Brachycera he adopts the following {457}arrangement: 1. Super-family Eremochaeta, for Stratiomyidae, Tabanidae, Acanthomeridae and Leptidae; 2. Tromoptera, for Nemestrinidae, Acroceridae, Bombyliidae, Therevidae, and Scenopinidae; 3. Energopoda, for Asilidae, Dolichopidae, Empidae and Lonchopteridae, Phoridae being included with doubt; 4. Mydaidae remains isolated.

This classification is based on the relations of the eyes and bristles of the upper surface, and on the powers of locomotion, aërial or terrestrial. At present it is not sufficiently precise to be of use to any but the very advanced student.

BLOOD-SUCKING DIPTERA.—The habit of blood-sucking from Vertebrates is, among Insects, of course confined to those with suctorial mouth, and is exhibited by various Diptera. It is, however, indulged in by but a small number of species, and these do not belong to any special division of the Order. It is remarkable that as a rule the habit is confined to the female sex, and that a large proportion of the species have aquatic larvae. This subject has many points of interest, but does not appear to have yet received the attention it merits. We give below a brief summary of the facts as to blood-sucking Diptera.

Series I. Nemocera.—In this section the habit occurs in no less than five
families, viz.:

Blepharoceridae. _Curupira_; in the female only; larva aquatic.

Culicidae. _Culex_, Mosquitoes; in the female only; other genera, with
one or two exceptions, do not suck blood; larvae aquatic.

Chironomidae. _Ceratopogon_, Midge; in the female only; exceptional
even in the genus, though the habit is said to exist in one or two less
known, allied genera; larval habits not certain; often aquatic; in _C.
bipunctatus_ the larva lives under moist bark.

Psychodidae. _Phlebotomus_: in the female only (?); quite exceptional
in the family; larva aquatic or in liquid filth.

Simuliidae. _Simulium_, sand-flies; general in the family (?), which,
however, is a very small one; larva aquatic, food probably mixed
vegetable and animal microscopic organisms.

Series II. Brachycera. Tabanidae. Gad-flies: apparently general in the
females of this family; the habits of the exotic forms but little known;
in the larval state, scarcely at all known; some are aquatic.

{458}Series IV. Cyclorrhapha Schizophora: _Stomoxys_, _Haematobia_; both
sexes (?); larvae in dung. [The Tse-tse flies, _Glossina_, are placed in
this family, though their mode of parturition is that of the next
section].

Series V. Pupipara. The habit of blood-sucking is probably common to all
the group and to both sexes. The flies, with one exception, frequent
Vertebrates; in many cases living entirely on their bodies, and
apparently imbibing much blood; the larvae are nourished inside the
flies, not on the imbibed blood, but on a milky secretion from the
mother.

Sub-Order Aphaniptera. Fleas. The habit of blood-sucking is common to all
the members and to both sexes. The larvae live on dried animal matter.

FOSSIL DIPTERA.—A considerable variety of forms have been found in amber, and many in the tertiary beds; very few members of the Cyclorrhaphous Sections are, however, among them; the Tipulidae, on the other hand, are richly represented. In the Mesozoic epoch the Order is found as early as the Lias, the forms being exclusively Orthorrhaphous, both Nemocera and Brachycera being represented. All are referred to existing families. Nothing has been found tending to connect the Diptera with other Orders. No Palaeozoic Diptera are known.

SERIES 1. ORTHORRHAPHA NEMOCERA

FAM. 1. CECIDOMYIIDAE.—_An extensive family of very minute and fragile flies, the wings of which have very few nervures; the antennae are rather long, and are furnished with whorls of hair._ In the case of some species the antennae are beautiful objects; in _Xylodiplosis_ some of the hairs have no free extremities, but form loops (Fig. 220). In the males of certain species the joints appear to be double, each one consisting of a neck and a body. Although comparatively little is known as to the flies themselves, yet these Insects are of importance on account of their preparatory stages. The larvae have very diverse habits; the majority live in plants and form galls, or produce deformations of the leaves, flowers, stems, buds, or roots in a great variety of ways; others live under bark or in animal matter; some are predaceous, killing Aphidae or Acari, and even other Cecidomyiids.

{459}

The North American _Diplosis resinicola_ lives in the resin exuded as the results of the attacks of a caterpillar. The larva burrows in the semi-liquid resin, and, according to Osten Sacken,[368] is probably amphipneustic. Cecidomyiid larvae are short maggots, narrowed at the two ends, with a very small head, and between this and the first thoracic segment (this bears a stigma), a small supplementary segment; the total number of segments is thirteen, besides the head; there are eight pairs of stigmata on the posterior part of the body. Brauer defines the Cecidomyiid larva thus, "peripneustic, with nine pairs of stigmata, the first on the second segment behind the head; two to nine on fifth to twelfth segments; body as a whole fourteen-segmented without a fully-formed head." The most remarkable peculiarity of Cecidomyiid larvae is that those of many species possess a peculiar organ—called breast-bone, sternal spatula, or anchor-process—projecting from the back of the lower face of the prothoracic segment. The use of so peculiar a structure has been much discussed. According to Giard,[369] in addition to the part {460}that protrudes externally, as shown in Fig. 219, A, there is a longer portion concealed, forming a sort of handle, having muscles attached to it. Some of these larvae have the power of executing leaps, and he states that such larvae are provided on the terminal segment with a pair of corneous papillae; bending itself almost into a circle, the larva hooks together the breast-bone and the papillae, and when this connection is broken the spring occurs. This faculty is only possessed by a few species, and it is probable that in other cases the spatula is used as a means for changing the position or as a perforator. Some of the larvae possess false feet on certain of the segments. Williston says they probably do not moult. In the pupal instar (Fig. 219, B), the Cecidomyiid greatly resembles a minute Lepidopterous pupa. The Hessian fly, _Cecidomyia destructor_, is frequently extremely injurious to crops of cereals, and in some parts of the world commits serious depredation. The larva is lodged at the point where a leaf enwraps the stem; it produces a weakness of the stem, which consequently bends. This Insect and _C. tritici_ (the larva of which attacks the flowers of wheat) pupate in a very curious manner: they form little compact cases like flax-seeds; these have been supposed to be a form of pupa similar to what occurs in the Blow-fly; but there are important distinctions. The larva, when about to undergo its change, exudes a substance from its skin, and this makes the flax-seed; the larval skin itself does not form part of this curious kind of cocoon, for it may be found, as well as the pupa, in the interior of the "flax-seed." Other Cecidomyiids form cocoons of a more ordinary kind; one species, described by Perris as living on _Pinus maritima_, has the very remarkable faculty of surrounding itself, by some means, with a cocoon of resin. Walsh describes the cocoon-forming process of certain Cecidomyiids as one of exudation and inflation; Williston as somewhat of the nature of crystallisation. Some Cecidomyiids are said to possess, in common with certain other Diptera, the unusual number of five Malpighian tubes; and Giard says that in the larva there is only a pair of these tubes, and that their extremities are united so as to form a single tube, which is twisted into an elegant double loop.

Thirty years or more ago the Russian naturalist, Wagner, made the very remarkable discovery that the larva of a Cecidomyiid produces young; and it has since been found by Meinert and {461}others that this kind of paedogenesis occurs in several species of the genera _Miastor_ and _Oligarces_. The details are briefly as follows:—A female fly lays a few, very large, eggs, out of each of which comes a larva, that does not go on to the perfect state, but produces in its interior young larvae that, after consuming the interior of the body of the parent larva, escape by making a hole in the skin, and thereafter subsist externally in a natural manner. This larval reproduction may be continued for several generations, through autumn, winter, and spring till the following summer, when a generation of the larvae goes on to pupation and the mature, sexually perfect fly appears. Much discussion has taken place as to the mode of origination of the larvae; Carus and others thought they were produced from the rudimental, or immature ovaries of the parent larva. Meinert, who has made a special study of the subject,[370] finds, however, that this is not the case; in the reproducing larva of the autumn there is no ovary at all; in the reproducing larvae of the spring-time rudimentary ovaries or testes, as the case may be, exist; the young are not, however, produced from these, but from germs in close connection with the fat-body. In the larvae that go on to metamorphosis the ovaries continue their natural development. It would thus appear that the fat-body has, like the leaf of a _Begonia_, under certain circumstances, the power, usually limited to the ovaries, of producing complete and perfect individuals.

Owing to the minute size and excessive fragility of the Gall-midge flies it is extremely difficult to form a collection of them; and as the larvae are also very difficult of preservation, nearly every species must have its life-history worked out as a special study before the name of the species can be ascertained. Notwithstanding the arduous nature of the subject it is, however, a favourite one with entomologists. The number of described and named forms cannot be very far short of 1000, and each year sees some 20 or 30 species added to the list. The number of undescribed forms is doubtless very large. The literature of the subject is extensive and of the most scattered and fragmentary character.

The Cecidomyiidae have but little relation to other Nemocera, and are sometimes called Oligoneura, on account of the reduced number of wing-nervures. Their larvae are of a peculiar type {462}that does not agree with the larvae of the allied families having well-marked heads (and therefore called Eucephala), nor with the acephalous maggots of Eumyiidae.

FAM. 2. MYCETOPHILIDAE.—_These small flies are much less delicate creatures than the Cecidomyiidae, and have more nervures in the wings; they possess ocelli, and frequently have the coxae elongated, and in some cases the legs adorned with complex arrangements of spines: their antennae have not whorls of hair._ Although very much neglected there are probably between 700 and 1000 species known; owing to many of their larvae living in fungoid matter the flies are called Fungus-gnats. We have more than 100 species in Britain. _Epidapus_ is remarkable, inasmuch as the female is entirely destitute of wings and halteres, while the male has the halteres developed but the wings of very reduced size. _E. scabiei_ is an excessively minute fly, smaller than a common flea, and its larva is said to be very injurious to stored potatoes. The larvae of Mycetophilidae are usually very elongate, worm-like maggots, but have a distinct, small head; they are peripneustic, having, according to Osten Sacken, nine pairs of spiracles, one pair prothoracic, the others on the first eight abdominal segments. They are usually worm-like, and sometimes seem to consist of twenty segments. Some of them have the faculty of constructing a true cocoon by some sort of spinning process, and a few make earthen cases for the purpose of pupation. The pupae themselves are free, the larval skin having been shed. The Mycetophilidae are by no means completely fungivorous, for many live in decaying vegetable, some even in animal, matter.

The habits of many of the larvae are very peculiar, owing to their spinning or exuding a mucus, that reminds one of snail-slime; they are frequently gregarious, and some of them have likewise, as we shall subsequently mention, migratory habits. Perris has described the very curious manner in which _Sciophila {463}unimaculata_ forms its slimy tracks;[371] it stretches its head to one side, fixes the tip of a drop of the viscous matter from its mouth to the surface of the substance over which it is to progress, bends its head under itself so as to affix the matter to the lower face of its own body; then stretches its head to the other side and repeats the operation, thus forming a track on which it glides, or perhaps, as the mucus completely envelops its body, we should rather call it a tunnel through which the maggot slips along. According to the description of Hudson[372] the so-called New Zealand Glow-worm is the larva of _Boletophila luminosa_; it forms webs in dark ravines, along which it glides, giving a considerable amount of light from the peculiarly formed terminal segment of the body. This larva is figured as consisting of about twenty segments. The pupa is provided with a very long, curiously-branched dorsal structure: the fly issuing from the pupa is strongly luminous, though no use can be discovered for the property either in it or in the larva. The larva of the Australian _Ceroplatus mastersi_ is also luminous. Another very exceptional larva is that of _Epicypta scatophora_; it is of short, thick form, like Cecidomyiid larvae, and has a very remarkable structure of the dorsal parts of the body; by means of this its excrement, which is of a peculiar nature, is spread out and forms a case for enveloping and sheltering the larva. Ultimately the larval case is converted into a cocoon for pupation. This larva is so different from that of other Mycetophilidae, that Perris was at first unable to believe that the fly he reared really came from this unusually formed larva. The larva of _Mycetobia pallipes_ (Fig. 221) offers a still more remarkable phenomenon, inasmuch as it is amphipneustic instead of peripneustic (that is to say, it has a pair of stigmata at the termination of the body and a pair on the first thoracic segment instead of the lateral series of pairs we have described as normal in Mycetophilidae). This larva lives in company with the amphipneustic larva of _Rhyphus_, a fly of quite another family, and the _Mycetobia_ larva so closely resembles that of the _Rhyphus_, that it is difficult to distinguish the two. This anomalous larva gives rise, like the exceptional larva of _Epicypta_, to an ordinary Mycetophilid fly.[373]

{464}But the most remarkable of all the Mycetophilid larvae are those of certain species of _Sciara_, that migrate in columns, called by the Germans, Heerwurm. The larva of _Sciara militaris_ lives under layers of decomposing leaves in forests, and under certain circumstances, migrates, sometimes perhaps in search of a fresh supply of food, though in some cases it is said this cannot be the reason. Millions of the larvae accumulate and form themselves by the aid of their viscous mucus into great strings or ribbons, and then glide along like serpents: these aggregates are said to be sometimes forty to a hundred feet long, five or six inches wide, and an inch in depth. It is said that if the two ends of one of these processions be brought into contact, they become joined, and the monstrous ring may writhe for many hours before it can again disengage itself and assume a columnar form. These processional maggots are met with in Northern Europe and the United States, and there is now an extensive literature about them.[374] Though they sometimes consist of almost incredible numbers of individuals, yet it appears that in the Carpathian mountains the assemblages are usually much smaller, being from four to twenty inches long. A species of _Sciara_ is the "Yellow-fever fly" of the Southern United States. It appears that it has several times appeared in unusual numbers and in unwonted localities at the same time as the dreaded disease, with which it is popularly supposed to have some connection.

FAM. 3. BLEPHAROCERIDAE.[375]—_Wings with no discal cell, but with a secondary set of crease-like lines._ The flies composing this small family are very little known, and appear to be obscure Insects with somewhat the appearance of Empidae, though with strongly iridescent wings; they execute aerial dances, after the manner of midges, and are found in Europe (the Pyrenees, Alps and Harz mountains) as well as in North and South America. Their larvae are amongst the most remarkable of Insect forms; indeed, no entomologist recognises them as belonging to a Hexapod Insect when he makes a first {465}acquaintance with them. The larva of _Curupira_ (Fig. 222) lives in rapid streams in Brazil, fixed by its suckers to stones or rocks. It consists only of six or seven divisions, with projecting side-lobes; the usual segmentation not being visible. There are small tracheal gills near the suckers, and peculiar scale-like organs are placed about the edges of the lobes. Müller considers that the first lobe is "cephalothorax," corresponding to head, thorax and first abdominal segment of other larvae, the next four lobes he considers to correspond each to an abdominal segment, and the terminal mass to four segments. He also says that certain minute points existing on the surface, connected with the tracheal system by minute strings, represent nine pairs of spiracles. These larvae and their pupae can apparently live only a short time after being taken out of the highly aërated water in which they exist, but Müller succeeded in rearing several flies from a number of larvae and pupae that he collected, and, believing them to be all one species, he announced that the females exhibited a highly developed dimorphism, some of them being blood-suckers, others honey-suckers. It is however, more probable that these specimens belonged to two or three distinct species or even genera. This point remains to be cleared up. The larva we have figured is called by Müller _Paltostoma torrentium_. It is certain, however, that the Brazilian Insect does not belong to the genus _Paltostoma_, and it will no doubt bear the name used by Osten Sacken, viz. _Curupira_.

The metamorphoses of the European _Liponeura brevirostris_ have been partially examined by Dewitz, who found the Insects in the valley of the Ocker in September.[376] He does not consider the "cephalothorax" to include an abdominal segment; and he found that two little, horn-like projections from the thorax of the {466}pupa are really each four-leaved. The pupa is formed within the larval skin, but the latter is subsequently cast so that the pupa is exposed; its dorsal region is horny, but the under surface, by which it clings firmly to the stones of the rapid brook, is white and scarcely chitinised, and Dewitz considers that the chitinous exudation from this part is used as a means of fastening the pupa to the stones. Blepharoceridae possess, in common with _Culex_, _Psychoda_ and _Ptychoptera_, the peculiar number of five Malpighian tubes, and it has been proposed by Müller to form these Insects into a group called Pentanephria.

FAM. 4. CULICIDAE (_Mosquitoes_, _Gnats_).—_Antennae with whorls of hair or plumes, which may be very dense and long in the male, though scanty in the female; head with a long, projecting proboscis._ Although there are few Insects more often referred to in general literature than Mosquitoes, yet the ideas in vogue about them are of the vaguest character. The following are the chief points to be borne in mind as to the prevalence of Mosquitoes:—The gently humming Gnat that settles on us in our apartments, and then bites us, is a Mosquito; there are a large number of species of Mosquitoes; in some countries many in one locality; in Britain we have ten or a dozen; notwithstanding the multiplicity of species, certain Mosquitoes are very widely diffused; the larvae are all aquatic, and specially frequent stagnant or quiet pools; they are probably diffused by means of the water in ships, it being known that Mosquitoes were introduced for the first time to the Hawaiian Islands by a sailing vessel about the year 1828. Hence it is impossible to say what species the Mosquitoes of a given locality may be without a critical examination. No satisfactory work on the Mosquitoes of the world exists. Urich states that he is acquainted with at least ten species in Trinidad. The species common in our apartments in Central and Southern England is _Culex pipiens_, Linn., and this species is very widely distributed, being indeed one of the troublesome Mosquitoes of East India. The term Mosquito is a Spanish or Portuguese diminutive of Mosca. It is applied to a variety of small flies of other families than Culicidae, but should be restricted to these latter. The irritation occasioned by the bites of Mosquitoes varies according to several circumstances, viz. the condition of the biter, the condition or constitution of the bitten, and also the species of Mosquito. Réaumur and {467}others believed that some irritating fluid is injected by the Mosquito when it bites. But why should it want to irritate as well as to bite? Macloskie, considering that the Mosquito is really a feeder on plant-substances, suggests that the fluid injected may be for the purpose of preventing coagulation of the plant-juices during the process of suction. It is a rule that only the female Mosquito bites, the male being an inoffensive creature, and provided with less effectual mouth-organs; it has, however, been stated by various authors that male Mosquitoes do occasionally bite. It is difficult to understand the blood-sucking propensities of these Insects; we have already stated that it is only the females that suck blood. There is reason to suppose that it is an acquired habit; and it would appear that the food so obtained is not essential to their existence. It has indeed been asserted that the act is frequently attended with fatal consequences to the individual that does it. The proper method of mitigating their nuisance is to examine the stagnant waters in localities where they occur, and deal with them so as to destroy the larvae. These little creatures are remarkable from the heads and thorax being larger and more distinct than in other Dipterous larvae. Their metamorphoses have been frequently described, and recently the numerous interesting points connected with their life-histories have been admirably portrayed by Professor Miall,[377] in an accessible form, so that it is unnecessary for us to deal with them. _Corethra_ is placed in Culicidae, but the larva differs totally from that of _Culex_; it is predaceous in habits, is very transparent, has only an imperfect tracheal system, without spiracles, and has two pairs of air-sacs (perhaps we should rather say pigmented structures possibly for aerostatic purposes, but not suppliers of oxygen). The kungu cake mentioned by Livingstone as used on Lake Nyassa is made from an Insect which occurs in profusion there, and is compressed into biscuit form. It is believed to be a _Corethra_. One of the peculiarities of this family is the prevalence of scales on various parts of the body, and even on the wings: the scales are essentially similar to those of Lepidoptera. Though Mosquitoes are generally obscure plain Insects, there are some—in the South American genus _Megarrhina_—that are elegant, beautifully adorned creatures. Swarms of various species of Culicidae, consisting sometimes of almost incalculable numbers {468}of individuals, occur in various parts of the world; one in New Zealand is recorded as having been three-quarters of a mile long, twenty feet high, and eighteen inches thick. There is good reason for supposing that Mosquitoes may act as disseminators of disease, but there is no certain evidence on the subject. The minute _Filaria_ that occurs in great numbers in some patients, is found in the human body only in the embryonic and adult conditions. Manson considers that the intermediate stages are passed in the bodies of certain Mosquitoes.[378]

FAM. 5. CHIRONOMIDAE (_Gnats_, _Midges_).—_Small or minute flies of slender form, with narrow wings, without projecting rostrum, usually with densely feathered antennae in the male, and long slender legs._ The flies of this family bear a great general resemblance to the Culicidae. They are much more numerous in species, and it is not improbable that we have in this country 200 species of the genus _Chironomus_ alone. They occur in enormous numbers, and frequently form dancing swarms in the neighbourhood of the waters they live in. The species are frequently extremely similar to one another, though distinguished by good characters; they are numerous about Cambridge. Many of them have the habit of using the front legs as feelers rather than as means of support or locomotion. This is the opposite of what occurs in Culicidae, where many of the species have a habit of holding up the hind legs as if they were feelers. The eggs of _Chironomus_ are deposited as strings surrounded by mucus, and are many of them so transparent that the development of the embryo can be directly observed with the aid of the microscope. They are said to possess a pair of air-sacs. The larvae, when born, are aquatic in habits, and are destitute of tracheal system. They subsequently differ greatly from the larvae of _Culex_, inasmuch as the tracheal system that develops is quite closed, and in some cases remains rudimentary. There is, however, much diversity in the larvae and also in the pupae. The little Blood-worms, very common in many stagnant and dirty waters, and used by anglers as bait, are larvae of _Chironomus_. They are said to be αἱ Ἐμπίδες of Aristotle. The red colour of these larvae is due to haemoglobin, a substance which has the power of attracting and storing oxygen, and giving it off to the tissues as they require it. Such larvae are able to live in burrows they construct {469}amongst the mud. Some of them, provided plentifully with haemoglobin, are in consequence able to live at great depths, it is said even at 1000 feet in Lake Superior, and come to the surface only occasionally. A few are able even to tolerate salt water, and have been fished up from considerable depths in the sea. It is a remarkable fact that these physiological capacities differ greatly within the limits of the one genus, _Chironomus_, for some of these species are destitute of haemoglobin, and have to live near the surface of the water; these have a superior development of the tracheal system. The pupae of _Chironomus_ have the legs coiled, and the thorax, instead of being provided with the pair of tubes or trumpets for breathing that is so common in this division of Diptera, have a pair of large tufts of hair-like filaments.[379] A very curious form of parthenogenesis has been described by Grimm[380] as existing in an undetermined species of _Chironomus_, inasmuch as the pupa deposits eggs. Although this form of parthenogenesis is of much interest, it is not in any way to be compared with the case, already referred to, of _Miastor_ (p. 461). The "pupa" is at the time of oviposition practically the imago still covered by the pupal integument; indeed Grimm informs us that in some cases, after depositing a small number of ova, the pupa became an imago. This parthenogenesis only occurs in the spring-generation; in the autumn the development goes on in the natural manner. The case is scarcely entitled to be considered as one of paedogenesis.

Gnats of this family, and believed to be a variety of _Chironomus plumosus_, are subject to a curious condition, inasmuch as individuals sometimes become luminous or "phosphorescent"; this has been noticed more specially in Eastern Europe and Western Asia. The whole of the body and legs may exhibit the luminous condition, but not the wings. It has been suggested by Schmidt that this condition is a disease due to bacteria in the body of the gnat.[381]

_Ceratopogon_ is a very extensive genus, and is to some extent anomalous as a member of Chironomidae. The larvae exhibit considerable variety of form. Some of them are aquatic {470}in habits, but the great majority are terrestrial, frequenting trees, etc. The former larvae are very slender, and move after the manner of leeches; they give rise to imagos with naked wings, while the terrestrial larvae produce flies with hairy wings. There are also important distinctions in the pupae of the two kinds; the correlation between the habits, and the distinctions above referred to, is, however, far from being absolutely constant.[382] Certain species of midges are in this country amongst the most annoying of Insects; being of very minute size, scarcely visible, they settle on the exposed parts of the body in great numbers, and by sucking blood create an intolerable irritation. _Ceratopogon varius_ is one of the most persistent of these annoyers in Scotland, where this form of pest is much worse than it is in England; in Cambridgeshire, according to Mr. G. H. Verrall, the two troublesome midges are the females of _C. pulicaris_ and _C. bipunctatus_.

FAM. 6. ORPHNEPHILIDAE.—_Small, brown or yellowish flies, bare of pubescence, with very large eyes contiguous in both sexes, and with antennae composed of two joints and a terminal bristle; both the second joint and the bristle are, however, really complex._ One of the smallest and least known of the families of Diptera, and said to be one of the most difficult to classify. The nervures of the wings are very distinct. Nothing is known of the habits and metamorphoses; there is only one genus—_Orphnephila_; it is widely distributed; we have one species in Britain.

FAM. 7. PSYCHODIDAE (_Moth-flies_).—_Extremely small, helpless flies, usually with thickish antennae, bearing much hair, with wings broader than is usual in small flies, and also densely clothed with hair, giving rise to a pattern more or less vague._ These flies are very fragile creatures, and are probably numerous in species. In Britain forty or fifty species have been recognised.[383] A South European form is a blood-sucker, and has received the appropriate name of _Phlebotomus_. The life-history of _Pericoma canescens_ has recently been studied by Professor Miall.[384] The larva is of aquatic habits, but is amphibious, being capable of existing in the air; it has a pair of anterior spiracles, by means {471}of which it breathes in the air, and a pair at the posterior extremity of the body, surrounded by four ciliated processes, with which it forms a sort of cup for holding air when it is in the water. The favourite position is amongst the filaments of green algae on which it feeds. A much more extraordinary form of larva from South America, doubtless belonging to this family, has recently been portrayed by Fritz Müller, under the name of _Maruina_.[385] These larvae live in rapid waters in company with those of the genus _Curupira_, and like the latter are provided with a series of suctorial ventral discs. Fritz Müller's larvae belong to several species, and probably to more than one genus, and the respiratory apparatus at the extremity of the body exhibits considerable diversity among them.

FAM. 8. DIXIDAE.—The genus _Dixa_ must, it appears, form a distinct family allying the Culicid series of families to the Tipulidae. The species are small, gnat-like Insects, fond of damp places in forests. We have four British species (_D. maculata_, _D. nebulosa_, _D. aestivalis_, _D. aprilina_). The genus is very widely distributed, occurring even in Australia. The larvae are aquatic, and have been described by Réaumur, Miall, and Meinert. The pupa has the legs coiled as in the Culicidae.

FAM. 9. TIPULIDAE (_Daddy-long-legs, or Crane-flies_).—_Slender Insects with elongate legs, a system of wing-nervures, rather complex, especially at the tip; an angulate, or open V-shaped, suture on the dorsum of the thorax in front of the wings: the female with the body terminated by a pair of hard, pointed processes, concealing some other processes, and forming an ovipositor._ The curious, silly Insects called daddy-long-legs are known all over the world, the family being a very large one, and found everywhere, some of its members extending their range even to the most inclement climates. It includes a great variety of forms that would not be recognised by the uninitiated, but can be readily distinguished by the characters mentioned above. It is impossible to assign any reason of utility for the extreme elongation of the legs of these Insects; as everyone knows, they break off with great ease, and the Insect appears to get on perfectly well without them. It is frequently {472}the case that they are much longer in the males than in the females. Other parts of the body exhibit a peculiar elongation; in some forms of the male the front of the head may be prolonged into a rostrum. In a few species the head is separated by a great distance from the thorax, the gap being filled by elongate, hard, cervical sclerites; indeed it is in these Insects that the phenomenon, so rare in Insect-structure, of the elongation of these sclerites and their becoming a part of the actual external skeleton, reaches its maximum. In several species of _Eriocera_ the male has the antennae of extraordinary length, four or five times as long as the body, and, strange to say, this elongation is accompanied by a reduction in the number of the segments of which the organ is composed, the number being in the male about six, in the female ten, in place of the usual fourteen or sixteen. In _Toxorrhina_ and _Elephantomyia_ the proboscis is as long as the whole body. In other forms the wings become elongated to an unusual extent by means of a basal stalk. It is probable that the elongation of the rostrum may be useful to the Insects. Gosse,[386] indeed, describes _Limnobia intermedia_ as having a rostrum half as long as the body, and as hovering like a Syrphid, but this is a habit so foreign to Tipulidae, that we may be pardoned for suspecting a mistake. The larvae exhibit a great variety of form, some being terrestrial and others aquatic, but the terrestrial forms seem all to delight in damp situations, such as shaded turf or rotten tree-stems. They are either amphipneustic or metapneustic, that is, with a pair of spiracles placed at the posterior extremity of the body; the aquatic species frequently bear appendages or projections near these spiracles. The pupae in general structure are very like those of Lepidoptera, and have the legs extended straight along the body; they possess a pair of respiratory processes on the thorax in the form of horns or tubes.

There are more than 1000 species of these flies known, and many genera. They form three sub-families, which are by some considered distinct families, viz.: Ptychopterinae, Limnobiinae or Tipulidae Brevipalpi, Tipulinae or Tipulidae Longipalpi.

The Ptychopterinae are a small group in which the angulate {473}suture of the mesonotum is indistinct; the larvae are aquatic and have the head free, the terminal two segments of the body enormously prolonged (Fig. 223), forming a long tail bearing, in the North American _Bittacomorpha_, two respiratory filaments. Hart[387] describes this tail as possessing a stigmatal opening at the extremity; no doubt the structure is a compounded pair of spiracles. The pupa (Fig. 223, B) has quite lost the respiratory tube at the posterior extremity of the body, but has instead quite as long a one at the anterior extremity, due to one tube of the pair normal in Tipulidae being enormously developed, while its fellow remains small. This is a most curious departure from the bilateral symmetry that is so constantly exhibited in Insect-structure. Our British species of _Ptychoptera_ have the pupal respiratory tube as extraordinary as it is in _Bittacomorpha_, though the larval tail is less peculiar.[388] This group should perhaps be distinguished from the Tipulidae as a separate family, but taxonomists are not yet unanimous as to this. Brauer considers that the head of the larva, and the condition of five Malpighian tubules in the imago, require the association of Ptychopterinae with the preceding families (Chironomidae, etc.), rather than with the Tipulidae.

The great majority of the Tipulidae are comprised in the sub-family Limnobiinae—the Tipulidae Brevipalpi of Osten Sacken:[389] in them the last joint of the palpi is shorter or not much longer than the two preceding together. They exhibit great variety, and many of them are types of fragility. The common winter gnats of the genus _Trichocera_ are a fair sample of this sub-family. The species of this genus mostly inhabit high latitudes, and delight in {474}a low temperature; it has been said that they may be seen on the wing in the depth of winter when the temperature is below freezing, but it is pretty certain that the spots chosen by the Insects are above that temperature, and Eaton states that the usual temperature during their evolutions is about 40° or 45° Fahr. They often appear in the damp conditions of a thaw when much snow is on the ground. _T. simonyi_ was found at an elevation of 9000 feet in the Tyrol, crawling at a temperature below the freezing-point, when the ground was deeply covered with snow. _T. regelationis_ occurs commonly in mines even when they are 500 feet or more deep. The most extraordinary of the Limnobiinae is the genus _Chionea_, the species of which are totally destitute of wings and require a low temperature. _C. araneoides_ inhabits parts of northern Europe, but descends as far south as the mountains near Vienna; it is usually said to be only really active in the depth of winter and on the surface of the snow. More recently, however, a large number of specimens were found by Professor Thomas in the month of October in his garden in Thuringia; they were caught in little pit-falls constructed to entrap snails. The larva of this Insect is one of the interesting forms that display the transition from a condition with spiracles at the sides of the body to one where there is only a pair at the posterior extremity.

A very peculiar Fly, in which the wings are reduced to mere slips, _Halirytus amphibius_, was discovered by Eaton in Kerguelen Land, where it is habitually covered by the rising tide. Though placed in Tipulidae, it is probably a Chironomid.

The group Cylindrotomina is considered by Osten Sacken[390] to be to some extent a primitive one having relationship with the Tipulinae; it was, he says, represented by numerous species in North America during the Oligocene period. It is of great interest on account of the larvae, which are in several respects similar to caterpillars of Lepidoptera. The larva of _Cylindrotoma distincta_ lives upon the leaves of plants—_Anemone_, _Viola_, _Stellaria_—almost like a caterpillar; it is green with a crest along the back consisting of a row of fleshy processes. Though this fly is found in Britain the larva has apparently not been observed here. The life-history of _Phalacrocera replicata_ has been recently published by Miall and Shelford.[391] The larva eats {475}submerged mosses in the South of England, and bears long forked filaments, reminding one of those of caterpillars. This species has been simultaneously discussed by Bengtsson, who apparently regards these Tipulids with caterpillar-like larvae—he calls them Erucaeformia[392]—as the most primitive form of existing Diptera.

The Tipulinae—Tipulidae Longipalpi, Osten Sacken[393]—have the terminal joint of the palpi remarkably long, longer than the three preceding joints together. The group includes the largest forms, and the true daddy-long-legs, a Chinese species of which, _Tipula brobdignagia_, measures four inches across the expanded wings. The group contains some of the finest Diptera. Some of the exotic forms allied to _Ctenophora_ have the wings coloured in the same manner as they are in certain Hymenoptera, and bear a considerable resemblance to members of that Order.

FAM. 10. BIBIONIDAE.—_Flies of moderate or small size, sometimes of different colours in the two sexes, with short, thick, straight, antennae; front tibiae usually with a long pointed process; coxae not elongate. Eyes of male large, united, or contiguous in front._ The flies of the genus _Bibio_ usually appear in England in the spring, and are frequently very abundant; they are of sluggish habits and poor performers on the wing.

{476}

The difference in colour of the sexes is very remarkable, red or yellow predominating in the female, intense black in the male; and it is a curious fact that the same sexual distinction of colour reappears in various parts of the world—England, America, India, and New Zealand; moreover, this occurs in genera that are by no means closely allied, although allied species frequently have concolorous sexes. The eyes of the males are well worth study, there being a very large upper portion, and, abruptly separated from this, a smaller, differently faceted lower portion, practically a separate eye; though so largely developed the upper eye is in some cases so hairy that it must greatly interfere with the formation of a continuous picture. Carrière considers that the small lower eye of the male corresponds to the whole eye of the female. The larvae of _Bibio_ (Fig. 225) are caterpillar-like in form, have a horny head, well developed, biting mouth-organs, and spine-like processes on the body-segments. They are certified by good authorities[394] to possess the extremely unusual number of ten pairs of spiracles; a larva found at Cambridge, which we refer to _Bibio_ (Fig. 225) has nine pairs of moderate spiracles, as well as a large terminal pair separated from the others by a segment without spiracles. The genus _Dilophus_ is closely allied to _Bibio_, the larvae of which (and those of Bibionidae in general) are believed to feed on vegetable substances; the parasitism of _Dilophus vulgaris_ on the larva of a moth, _Epinotia_ (_Chaetoptria_) _hypericana_, as recorded by Meade,[395] must therefore be an exceptional case. In the genus _Scatopse_ there is a very important point to be cleared up as to the larval respiratory system; it is said by Dufour and Perris[396] to be amphipneustic; there are, however, nine projections on each side of the body that were considered by Bouché, and probably with good reason, to {477}be spiracles. The food of _Scatopse_ in the larval state is principally vegetable. The larva of _Scatopse_ changes to a pupa inside the larval skin; the pupa is provided on the thorax with two branched respiratory processes that project outside the larval skin.[397] Lucas has given an interesting account of the occurrence of the larva of _Bibio marci_ in enormous numbers at Paris; they lived together in masses, there being apparently some sort of connection between the individuals.[398] In the following year the fly was almost equally abundant.

Owing to the great numbers in which the species of Bibionidae sometimes appear, these Insects have been supposed to be very injurious. Careful inquiry has, however, generally exculpated them as doers of any serious injury, though _Dilophus febrilis_—a so-called fever-fly—appears to be really injurious in this country when it multiplies excessively, by eating the roots of the hop-plant.

FAM. 11. SIMULIIDAE (_Sand-flies_, _Buffalo-gnats_).—_Small obese flies with humped back, rather short legs and broad wings, with short, straight antennae destitute of setae; proboscis not projecting._ There is only one genus, _Simulium_, of this family, but it is very widely spread, and will probably prove to be nearly cosmopolitan. Some of the species are notorious from their blood-sucking habits, and in certain seasons multiply to an enormous extent, alight in thousands on cattle, and induce a disease that produces death in a few hours; it is thought as the result of an instilled poison. _S. columbaczense_ has occasioned great losses amongst the herds near the Danube; in North America the Buffalo- and Turkey-gnats attack a variety of mammals and birds. In Britain {478}and other parts of the world they do not increase in numbers to an extent sufficient to render them seriously injurious: their bite is however very annoying and irritating to ourselves. In their early stages they are aquatic and require well aërated waters: the larvae hold themselves erect, fixed to a stone or some other object by the posterior extremity, and have on the head some beautiful fringes which are agitated in order to bring food within reach; the pupae are still more remarkable, each one being placed in a pouch or sort of watch-pocket, from which projects the upper part of the body provided with a pair of filamentous respiratory processes. For an account of the interesting circumstances connected with the metamorphoses of this species the reader should refer to Professor Miall's book; and for the life-history of the American Buffalo-gnat to Riley.[399]

FAM. 12. RHYPHIDAE.—This is another of the families that have only two or three genera, and yet are very widely distributed. These little flies are distinguished from other Nemocera Anomala (cf. p. 456) by _the presence of a discal cell; the empodia of the feet are developed as if they were pulvilli, while the true pulvilli remain rudimentary_. The larvae are like little worms, being long and cylindric; they are amphipneustic, and have been found in decaying wood, in cow-dung, in rotten fruits, and even in dirty water. The "petite tipule," the metamorphoses of which were described and figured by Réaumur, is believed to be the common _Rhyphus fenestralis_.[400] _R. fenestralis_ is often found on windows, as its name implies.

SERIES 2. ORTHORRHAPHA BRACHYCERA

FAM. 13. STRATIOMYIDAE.—_Antennae with three segments and a terminal complex of obscure joints, frequently bearing an arista: tibiae not spined; wings rather small, the anterior nervures usually much more strongly marked than those behind. The median cell small, placed near to the middle of the wing. Scutellum frequently spined; terminal appendages of the tarsi small, but pulvilli and a pulvilliform empodium are {479}present._ This is a large family, whose members are very diversified, consequently definition of the whole is difficult. The species of the typical sub-family Stratiomyinae generally have the margins of the body prettily marked with green or yellow, and the scutellum spined. In the remarkable American genus, _Hermetia_, the abdomen is much constricted at the base, and the scutellum is not spined; in the division Sarginae the body is frequently of brilliant metallic colours. The species all have an only imperfect proboscis, and are not blood-suckers. The larvae are also of diverse habits; many of those of the Stratiomyinae are aquatic, and are noted for their capacity of living in salt, alkaline, or even very hot water. Mr. J. C. Hamon found some of these larvae in a hot spring in Wyoming, where he could not keep his hand immersed, and he estimated the temperature at only 20° or 30° Fahr. below the boiling-point. The larva of _Stratiomys_ is of remarkably elongate, strap-like, form, much narrowed behind, with very small head; the terminal segment is very long and ends in a rosette of hairs which the creature allows to float at the surface. After the larval skin is shed the pupa, though free, is contained therein; the skin alters but little in form, and has no organic connection with the pupa, which merely uses the skin as a shield or float. These larvae have been very frequently described; they can live out of the water. Brauer describes the larvae of the family as "peripneustic, some perhaps amphipneustic." Miall says there are, in _Stratiomys_, nine pairs of spiracles on the sides of the body which are not open, though branches from the longitudinal air-tubes pass to them. There are probably upwards of 1000 species of Stratiomyidae known, and in Britain we have 40 or 50 kinds. The American genus _Chiromyza_, Wied., was formerly treated by Osten Sacken as a separate family, Chiromyzidae, but Williston places it in Stratiomyidae.