Chapter XXII: Introduction: Habits–classification–structure–chilognatha–chilopoda (16)

The ant-lions in their perfect state are usually unattractive Insects, and many are nocturnal in their habits; the species of the genus _Palpares_ and allies (Fig. 299) are, however, of more handsome appearance, and attain a large expanse of wing. No member of the sub-family is an inhabitant of Britain, though species of the typical genus _Myrmeleon_ are common in Central and Northern Europe. The {455}remarkable habits of their larvae attracted the attention of naturalists so long ago as two hundred years. We owe to Réaumur an accurate and interesting account of _M. formicarius_, the species found in the neighbourhood of Paris. The larvae are predaceous, and secure their prey by means of pitfalls they excavate in the earth, and at the bottom of which they bury themselves, leaving only their elongate jaws projecting out of the sand at the bottom of the pit. They move only backwards, and in forming their pit use their broad body as a plough, and throw out the sand by placing it on the head and then sending it to a distance with a sudden jerk. When about to construct its trap the larva does not commence at the centre, but makes first a circular groove of the full circumference of the future pit. Burying its abdomen in the surface of the earth, the Insect collects on to its head, by means of the front leg, the sand from the side which is nearest to the centre, and then jerks the sand to a distance. By making a second circuit within the first one, and then another, the soil is gradually removed, and a conical pit is formed, at the bottom of which the ant-lion lurks, burying its body but leaving its formidable mandibles widely extended and projecting from the sand. In this position the young ant-lion waits patiently till some wandering Insect trespasses on its domains. An ant or fly coming over the edge of the pitfall finds the sand of the sloping sides yielding beneath its body, and in its effort to secure itself probably dislodges some more of the sand, which, descending to the bottom of the pit, brings the lurking lion into activity. Availing himself of his power of throwing sand with his head, the ant-lion jerks some in the neighbourhood of the trespasser, and continues to do so until the victim is brought to the bottom of the pit and into the very jaws of its destroyer; then there is no further hope of escape; the mandibles close, empale their prey, and do not relax their hold till the body of the victim is exhausted of its juices. The position chosen is in a place that will keep dry, as the larva cannot carry on its operations when the sand is wet or damp, hence the soil at the base of a high wall or a rock frequently harbours these Insects.

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The parts of the mouth of the _Myrmeleon_ are perfectly adapted for enabling it to empty the victim without for a moment relaxing its hold. There is no mouth-orifice of the usual character, and the contents of the victim are brought into the buccal cavity by means of a groove extending along the under side of each mandible; in this groove the elongate and slender lobe that replaces the maxilla—there being no maxillary palpi—plays backwards and forwards, probably raking or dragging backwards to the buccal cavity at each movement a small quantity of the contents of the empaled victim. The small lower lip is peculiar, consisting in greater part of the two lobes that support the labial palpi. The pharynx is provided with a complex set of muscles, and, together with the buccal cavity, functions as an instrument of suction. After the prey has been sucked dry the carcass is jerked away to a distance. When the ant-lion larva is full grown it forms a globular cocoon by fastening together grains of sand with fine silk from a slender spinneret placed at the posterior extremity of the body; in this cocoon it changes to an imago of very elongate form, and does not emerge until its metamorphosis is quite completed, the skin of the pupa being, when the Insect emerges, left behind in the cocoon. The names by which the European ant-lion has been known are very numerous. It was called Formicajo and Formicario by Vallisneri about two hundred years ago; Réaumur called it Formica-leo, and this was adopted by some modern authors as a generic name for some other of the ant-lions. The French people call these Insects Fourmilions, of which ant-lion is our English equivalent. The Latinised form of the term ant-lion, Formicaleo, is not now applied to the common ant-lion as a generic term, it having been proposed to replace it by _Myrmecoleon_, _Myrmeleo_, or _Myrmeleon_; this latter name at present seems likely to become generally adopted. There are several species of the genus found in Europe, and their trivial names have been confounded by various authors in such a way as to make it quite uncertain, without reference to a synonymic list, what species is intended by any particular writer. The species found in the neighbourhood of Paris, and to which it may be presumed Réaumur's history refers, is now called {457}_Myrmeleon formicarium_ by Hagen and others; M‘Lachlan renamed it _M. europaeus_, but now considers it to be the _M. nostras_ of Fourcroy. The popular name appears to be due to the fact that ants—Formica in Latin, Fourmi in French—form a large part of the victims; while lion—the other part of the name—is doubtless due to its prowess as a destroyer of animal life, though, as Réaumur long ago remarked, it is a mistake to apply the term lion to an Insect that captures its prey by strategy and by snares rather than by rapidity and strength. The imago of _Myrmeleon_ is of shy disposition, and is rarely seen even in localities where the larva is abundant. It is of nocturnal habits, and is considered by Dufour to be carnivorous.

Considerable difference of opinion has existed as to the structure of the mouth and of the alimentary canal in these larvae. Réaumur was of opinion that there exists no posterior orifice to the alimentary canal, but Dufour ridiculed this idea, and stated positively that such an orifice undoubtedly exists. It is also usually said that the mouth is closed by a membrane. Meinert has recently examined these points,[381] and he states that the mouth is not closed by any membrane, but is merely compressed. He finds that there is no posterior exit from the stomach; that there is a compact mass without any cavity between the stomach and the point where the Malpighian tubes connect with the small intestine. The portions of aliment that are not assimilated by the larva collect in the stomach and are expelled as a mass, but only after the Insect has become an imago. This peculiar excrementitious mass consists externally of uric acid, and from its form and appearance has been mistaken for an egg by several naturalists. The posterior portions of the alimentary canal are, according to Meinert, of a remarkable nature. The small intestine is elongate, slender, and is coiled. There are eight very long and slender Malpighian tubes; a pair of these have free extremities, but the other six in the posterior part of their course are surrounded by a common membrane, and, following the course of the intestine, form ultimately a dilated body seated on a coecum. These six Malpighian tubes are considered to be partially, if not entirely, organs for the secretion of silk for forming the cocoon, the coecum being a reservoir. The canal terminates as a slender tube, which acts as a spinneret and is surrounded by a sheath. A complex set of muscles {458}completes this remarkable spinning apparatus. The alimentary canal of the imago has been described and figured by Dufour[382]; it is very different from that of the larva.

The ant-lion is capable of sustaining prolonged fasts. Dufour kept specimens for six months without any food. These Insects are said to give off a peculiar ant-like odour, due, it is thought, to their ant-eating habits. Although no species inhabits Great Britain, yet one is found in Southern Sweden. Introduced specimens get on very well in confinement in our country,[383] and would probably flourish at large for some years if they were liberated.

Although the number of known species and genera of Myrmeleonides is considerable—that of the species being now upwards of 300—the members of the small genus _Myrmeleon_ are the only forms that are known to make pits of the kind we have described. Other larvae[384] are known similar in general form to the common ant-lion, but they walk forwards in the normal manner, and apparently hunt their prey by lurking in a hidden place and, when a chance occurs, rushing on the victim with rapidity. Brauer has observed this habit in the case of _Dendroleon pantherinus_ in the Prater at Vienna.

The most remarkable forms of Myrmeleonides are contained in the genus _Palpares_. We figure _Tomateres citrinus_ (Fig. 299), an allied genus found in Eastern Africa as far south as Natal. These Insects have conspicuous blotches and marks on their wings. The species of _Myrmeleon_ are similar in form, but are smaller, more feeble, and less ornate in appearance.

{459}Pitfalls, formed in all probability by ant-lions, have been noticed in the Galapagos islands and in Patagonia, though none of the Insects forming them have been found.

SUB-FAM. 2. ASCALAPHIDES.—_Antennae elongate, with a knob at the tip; the
apical area of the wing with irregular cellules._

The sub-family Ascalaphides is not represented by any species in Britain, though _Ascalaphus longicornis_ occurs as far north as Paris. In the mountainous regions of Central and Southern Europe some species of the group form a conspicuous part of the Insect fauna, owing to their bold and active flight; they are predaceous in their habits, and fly about in a hawking fashion somewhat like that of dragon-flies. Some of the larger of the numerous exotic species of the group are very like dragon-flies, but can be distinguished by a glance at the elongate antennae with a knob at the end. The sub-family consists of two groups—Holophthalmi and Schizophthalmi. M‘Lachlan says[385]: "The eyes in the Schizophthalmous division are really double, the upper portion overlapping the under; if the upper portion be separated the lower division looks like a small spherical ordinary eye." There appears, however, to be considerable differences in the genera in this respect.

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When the weather is wet or cold the Ascalaphi repose on the stems of grass, with their wings placed in a roof-like manner, with the head downwards, and are then very successful in concealing themselves by the positions they assume, and by sidling round the stems to escape from enemies. Some information as to their metamorphosis has been obtained, though knowledge of this point is far from complete even as regards our European species of the typical genus _Ascalaphus_. For a long time it was supposed that a larva mentioned by Bonnet in his writings was that of _Ascalaphus_, but Brauer[386] is of opinion that such is not the case, and as he has described the metamorphoses of _A. macaronius_ he is no doubt correct. The eggs (Fig. 303, A), forty or fifty in number, are laid in two parallel rows on the stems of grass. The larvae (Fig. 304, larva of _Helicomitus_ ?) are in general appearance somewhat like those of _Myrmeleon_; they are carnivorous in their habits, like the ant-lions, and have similar extraordinarily developed mandibles. Efforts to rear the young larvae failed, but they were kept alive for some time by supplying them with Aphidides found on _Centaurea jacea_. The cocoon is globular, and the change from the nymph state to the imago is made in the cocoon, the structure of the mandibles of the pupa being peculiar, and specially adapted to the purpose of opening the cocoon.[387] The larvae of Ascalaphides, although so like the ant-lions in appearance, do not form pitfalls for the capture of their prey, but lurk under leaves on the ground, or under stones; they do not move backwards, but progress forwards in an ordinary manner; the habit of backward movement that we noticed in _Myrmeleon_ being probably correlative with the habit of forming pitfalls. Hagen states[388] that the larvae of Ascalaphides and Myrmeleonides, in addition to their peculiarities of form and mandibular structure, are distinguished from those of other Hemerobiidae by the hind legs having the tibia and tarsus united {461}without articulation. Westwood[389] has recently given an account of the young larvae of a Ceylonese Ascalaphid of doubtful species, but possibly _Helicomitus insimulans_; these were observed by Mr. Staniforth Green to have the very peculiar habit of sitting together in a long row on the stem of a plant, with the jaws widely extended and the body of each one covered by the head of the individual next it (Fig. 303, B). The little creatures waited patiently in this position until a fly walked between the mandibles of one of them, then these formidable weapons immediately closed, and did not relax their hold until the fly was sucked dry. If Westwood is correct, the young larva of this species differs much from the adult one, the back of the head being broad and the setigerous processes of the body very much more developed. Nearly thirty genera of Ascalaphides are known.[390] In the genus _Haplogenius_ we find an exception to the usual rule that the wings in repose are held in a roof-like manner, it having been noticed by Bates that in the species in question the wings are held expanded as in the dragon-flies.

Guilding has described[391] a very peculiar mode of oviposition on the part of _Ulula macleayana_ in the island of St. Vincent; the eggs are said to be deposited by the female in circles on the extremity of a twig, and nearer the base of this there is placed a kind of barrier to repel intruders. "The female may be seen expelling from her ovary these natural barriers with as much care as her real eggs." Guilding's description was accompanied by drawings of the eggs, barriers and larvae, but unfortunately these were never published, and no further information has been obtained on the subject. Hagen[392] suggests that the barriers may {462}be somewhat similar to the long stalks on which the eggs of _Chrysopa_ (Fig. 314) are placed.

SUB-FAM. 3. NEMOPTERIDES.—_Head more or less produced and beak-like. Hind
wings of peculiar form, being elongate and somewhat strap-like._

The Nemopterides are a small group of delicate, graceful Insects. About thirty species are known. Knowledge of the group is still very imperfect. A larva has been found of a most remarkable nature that probably belongs to it; it was described under the name of _Necrophilus arenarius_, and considered to be a fully-developed Insect. This larva occurs in the tombs and pyramids of Egypt where sand has accumulated. The perfect Insects of the genus _Nemoptera_ are, however, found in open places amongst bushes, and flit about in a very graceful manner. Several species are found in Southern Europe and the Mediterranean region {463}(Fig. 305, _N. ledereri_), but none come so far north as Central Europe. Formerly the genus _Nemoptera_ was considered to be allied to _Panorpa_ on account of the beak-like front of the head. The parts of the mouth are, however, different from those of _Panorpa_, and it seems more probable that if the Nemopterides have to be merged in any of the divisions of Hemerobiidae, they will be placed in Chrysopides or Osmylides. The species of the sub-family were for a long time believed to be peculiar to the continental regions of the Old World, but a species has recently been discovered in Northern Chili.[393]

SUB-FAM. 4. MANTISPIDES.—_Prothorax elongate; the raptorial front legs
inserted at its anterior part._

The members of this small group are readily recognised by the peculiar structure of the front legs; these organs resembling those of the Orthopterous family Mantidae, so that the earlier systematic entomologists, deceived by this resemblance, placed the Mantispides in the Order referred to.

The Mantispides possess four membranous wings, either sub-equal in size or the posterior pair smaller than the front pair and not folded; the veins of these wings are rather numerous, as are also the cells they form; there is considerable difference amongst the species in this latter respect, owing to the transverse veinlets differing in their abundance. The antennae are short, not in the least thickened at the tip. The head is not produced into a beak. The anterior legs, placed quite at the front part of the thorax, have the coxae very long; the femur is somewhat incrassate, and is armed on one side with spines; the tibia is shaped and articulated so as to fold closely on to the spines, and to thus constitute a formidable and perfect prehensile organ, the tarsus being merely a small appendage.

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Only a few species of _Mantispa_ are found in Southern Europe; but the group has representatives in most of the warmer regions of the world, and will probably prove to be rather numerous in species. The front legs are used for the capture of prey in the same way as the somewhat similar front legs of the Mantidae. The transformations have been observed by Brauer[394] in the case of one of the European species, _M. styriaca_. The eggs are numerous but very small, and are deposited in such a manner that each is borne by a long slender stalk, as in the lacewing flies. The larvae are hatched in autumn; they then hibernate and go for about seven months before they take any food. In the spring, when the spiders of the genus _Lycosa_ have formed their bags of eggs, the minute _Mantispa_ larvae (Fig. 308, A) find them out, tear a hole in the bag, and enter among the eggs; here they wait until the eggs have attained a fitting stage of development before they commence to feed. Brauer found that they ate the spiders when these were quite young, and then changed their skin for the second time, the first moult having taken place when they were hatched from the egg. At this second moult the larva undergoes a considerable change of form; it becomes unfit for locomotion, and the head loses the comparatively large size and high development it previously possessed. The _Mantispa_ larva—only one of which flourishes in one egg-bag of a spider—undergoes this change in the midst of a mass of dead young spiders it has gathered together in a peculiar manner. It undergoes no further change of skin, and is full fed in a few days; after which it spins a cocoon in the interior of the egg-bag of the spider, and changes to a nymph inside its larva-skin. {465}Finally the nymph breaks through the barriers—larva-skin, cocoon, and egg-bag of the spider—by which it is enclosed, and after creeping about for a little, appears in its final form as a perfect _Mantispa_. Thus in this Insect hypermetamorphosis occurs; the larval life consisting of two different instars, one of which is specially adapted for obtaining access to the creature it is to prey on. It should be noticed that though this Insect is so destructive to the young spiders, the mother spider shows no hostility to it, but allows the destroying larva to enter her bag of eggs without any opposition; she appears, indeed, to be so unconscious of the havoc that is going on amongst her young that in one case she continued to watch over and protect the egg-bag in which the destruction was taking place during the whole of the period of the larval development and half the period of pupation of the _Mantispa_.

The larval history of a second species of the Mantispides, _Symphrasis varia_, is partially known;[395] this Insect lives parasitically in the nests of a South American wasp, and each larva when full fed spins a cocoon in one of the cells of the Hymenopteron.

SUB-FAM. 5. HEMEROBIIDES.—_Wings in repose forming an angular roof over
the body; the antennae moniliform or pectinate, not clavate._

The Hemerobiides consist of several minor groups about whose number and characters systematists are not very well agreed, and about some of which very little is known. We merely mention the latter, giving details as to some of the better known only.

1. The Dilarina are a small group found chiefly in the Old World, where, however, they have a wide distribution. North and South America have each one species. They are distinguished by their antennae, which, in the male, are pectinate somewhat like those of many Lepidoptera, this character being of extremely rare occurrence in the Neuroptera; the abdomen of the female terminates in a long ovipositor. The metamorphoses are not known.

2. Nymphidina: Australian Insects resembling Myrmeleonides, but having antennae without club. Metamorphoses not known.

{466}3. Osmylina: a group of delicate and elegant Insects of small or moderate size, distinguished by the possession of three simple eyes placed on the middle of the head just above the antennae. A species of this group, _Osmylus chrysops_ (_maculatus_ of some authors), is an inhabitant of Britain (Fig. 212); its larva is to some extent amphibious. The metamorphoses have been observed by Dufour, Brauer, and Hagen;[396] it lurks under stones in or close to the water, or in moss, or on the stems of aquatic plants, and pierces and empties small Insects with its sucking-spears, which are very elongate. The young are hatched from the egg in the autumn and hibernate before becoming full grown; when this moment arrives the larva spins a round cocoon of silk mixed with sand. The pupa, or nymph, in general appearance somewhat resembles the perfect Insect, except that it is shorter and has the short wing-pads clinging close to the body. Dufour denied the existence of abdominal spiracles in either larva or imago, but, according to Hagen, they are certainly present in both. It would appear that in the larva the alimentary canal is not open beyond the chylific ventricle, and that its terminal section is modified to form a spinning apparatus.

_Osmylus_ and its allies, including _Sisyra_, are now frequently treated as a separate sub-family, Osmylides, equivalent to the Chrysopides. In it is placed a very anomalous Insect—_Psectra dispar_—of great rarity. The male has only two wings, the posterior pair being the merest rudiments, though the female has the four wings normally developed. Individuals of the male have been found[397] in widely separated localities in the Palaearctic region—Somersetshire being one of them—and also in North America.

{467}The genus _Sisyra_ forms for some Neuropterists the type of a separate group called Sisyrina, though by others it is placed, as we have said, with the Osmylina, though it is destitute of ocelli. The larvae of at least one species of this genus are aquatic, and have been found in abundance living in _Spongilla_ (_Ephydatia_) _fluviatilis_, a fresh-water sponge; when discovered their nature was not at first recognised, as they possess on each ventral segment a pair of articulated appendages, looking like legs, but which are considered to be more of the nature of gills. The sucking-spears of this Insect are so long and slender as to look like hairs; whether the little animal draws its nutriment from the sponge, or merely uses this latter as a place of shelter, is not ascertained.

4. Hemerobiina: a somewhat numerous group of small or more rarely moderate-sized Insects, with moniliform antennae, no ocelli, a complex and comparatively regular system of wing-nervures; the veinlets are especially numerous at the margins, owing to the mode of forking of the nervures there (Fig. 298, _Drepanepteryx phalaenoides_). The larvae of most of the species of which the habits are known {468}live on Aphides, which they suck dry, and at least one species, in all probability several, has the habit of covering itself with the skins of the victims it has sucked; to these remains it adds other small debris, and the whole mass completely covers and conceals the Insect (Fig. 311, B). The larva is furnished at the sides with projections which serve as pedicels to elongate divergent hairs, and these help to keep the mass in place on the back of the Insect; some fine threads are distributed through this curious mantle and serve to keep it from disintegration, but whether they are fragments of spiders' webs or are spun by the Insect itself is not quite clear.

The genus _Drepanepteryx_ consists of several species, and appears to be best represented in the Antipodes; we have, however, one species in Britain—_D. phalaenoides_ (Fig. 298)—an extremely interesting member of our fauna. This Insect has, like several of its congeners, a moth-like appearance, and it has a peculiar structure for bringing the hind and fore wings into correlation, the costa at the base of the hind wing being interrupted and prominent, furnished with setae (Fig. 312, A), and playing in a cavity on the under-surface of the front wing. This character is of great interest in connexion with analogous structures of a more perfect nature existing in various moths. M‘Lachlan has described and figured[398] a more primitive, though analogous, condition of the wings in _Megalomus hirtus_, also a species of British Hemerobiina. Another very curious feature of _D. phalaenoides_ is shown in Fig. 312, B, there being a narrow space on the hind part of the front wing from which the colour is absent, while the nervures appear to be interrupted; they are, however, really present, though transparent; the nature of this peculiar mark is quite unknown, but is of considerable interest in connexion with the small transparent spaces that exist on the wings of some butterflies.

{469}SUB-FAM. 6. CHRYSOPIDES, LACEWING-FLIES.—_Fragile Insects with
elongate, setaceous antennae._

The lacewing-flies—also called stink-flies and golden-eyes—are excessively delicate Insects, of which we possess about 15 species in Britain. Their antennae are more slender and less distinctly jointed than they are in Hemerobiides, and the Chrysopides are more elongate Insects. The peculiar metallic colour of their eyes is frequently very conspicuous, the eyes looking, indeed, as if they were composed of shining metal; this fades very much after death. Although not very frequently noticed, the Chrysopides are really common Insects, and are of considerable importance owing to their keeping "greenfly" in check.

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The eggs are very remarkable objects (Fig. 314), each one being supported at the top of a stalk many times as long as itself; in some species (_C. aspersa_) the eggs are laid in groups, those of each group being supported on a common stalk. The larvae (Fig. 315) are of a very voracious disposition, and destroy large quantities of plant-lice by piercing them with sucking-spears, the bodies of the victims being afterwards quickly exhausted of their contents by the action of the apparatus connected with the spears. The larvae of two or three species of _Chrysopa_ cover themselves with the skins of their victims after the manner of the larvae of _Hemerobius_; but most of the larvae of _Chrysopa_ are unclothed, and hunt their victims after the fashion of the larvae of Coccinellidae, to which these _Chrysopa_ larvae bear a considerable general resemblance. These larvae have a remarkable structure at the extremity of their feet, but its use is quite unknown (Fig. 315, B, C). Some larvae of the genus make use of various substances as a means of disguise or protection. Dewitz noticed[399] that some specimens he denuded of their clothing and placed in a glass, seized small pieces of paper with their mandibles and, bending the head, placed the morsels on their backs; here the pieces remained in consequence of the existence of hooked hairs on the skin. Green algae or cryptogams are much used for clothing, and Dewitz supposes that the Insect spins them together with webs to facilitate their retention. According to Constant and Lucas[400] the larvae of _Chrysopa_ attack and kill the larvae {471}of Lepidoptera and Phytophagous Hymenoptera. The curious form we figure (Fig. 316) has been hatched from eggs found by Brauer on _Pinus abies_ in Austria. The eggs were of the stalked kind we have described; the young escaped from them in the autumn, twelve days after deposition, but did not take any food till the following spring.

The Chrysopides are widely distributed over the earth's surface. They form an important part of the fauna of the Hawaiian islands.

SUB-FAM. 7. CONIOPTERYGIDES.—_Minute Insects with very few transverse
nervules in the wings; having the body and wings covered by a powdery
efflorescence._

These little Insects are the smallest of the Order Neuroptera, and have the appearance of winged Coccidae; their claim to be considered members of the Neuroptera was formerly doubted, but their natural history is quite concordant with that of the Hemerobiid groups, near which they are now always placed. Löw has made us acquainted with the habits and structure of an Austrian species, _Coniopteryx lutea_ Wallg., but for which he has proposed the new generic name _Aleuropteryx_; the larvae are found on _Pinus mughus_ at Vienna feeding on _Aspidiotus abietis_, which they pierce with sucking-spears, after the fashion of the Hemerobiides; when full fed they spin a cocoon formed of a double layer of silk, in which metamorphosis takes place in a manner similar to that of other Hemerobiidae. The better-known genus _Coniopteryx_ differs from _Aleuropteryx_ in having the sucking-spears short and nearly concealed by the front of the head, which is somewhat prolonged.

{472}We may conclude this sketch of the Hemerobiid groups by remarking that fossil remains of specimens of most of them have been detected in the Tertiary strata, and that in the Secondary strata these groups are represented by only a small number of fossils, which are referred specially to Hemerobiina, Nymphidina, and Chrysopides.

{473}CHAPTER XXI

NEUROPTERA _CONTINUED_—TRICHOPTERA, THE PHRYGANEIDAE OR CADDIS-FLIES

FAM. XI. PHRYGANEIDAE—CADDIS-FLIES.

(TRICHOPTERA OF MANY AUTHORS)

_Wings more or less clothed with hair, nervures dividing at very acute
angles, very few transverse nervules; hind pair larger than the front,
with an anal area which is frequently large and in repose plicately
folded. Antennae thread-like, porrect, of many indistinct joints.
Mandibles absent or obsolete. Coxae elongate and free but contiguous.
Metamorphosis great; larvae caterpillar-like, usually inhabiting cases of
their own construction. Pupa resembling the perfect Insect in general
form, becoming active previous to the last ecdysis. Wingless forms of the
imago excessively rare._

The caddis-flies are Insects of moth-like appearance, found in the neighbourhood of water; their larvae live in this element, where they may sometimes be found in abundance. Phryganeidae are not very attractive Insects, and there are few of large size; Hence they have been much neglected by entomologists, and very little is known about the exotic forms of the family. The habitations constructed by the larvae are, many of them, of a {474}curious nature, and usually attract more attention than do the creatures they serve to protect.

The Phryganeidae form the division or series Trichoptera; the two terms are therefore synonymous; those entomologists who consider these Insects to form a distinct Order use the latter appellation for it.

The perfect Insect, though the wings are usually ample, has but feeble powers of flight, and rarely ventures far from the water it was reared in; it has a moth-like appearance, and the wings in repose meet, at an angle, in a roof-like manner over the back (Fig. 326, E). The head is small, with the front inflexed; it has two large compound eyes, and usually three ocelli; the antennae are slender, thread-like, and occasionally attain a great length. The parts of the mouth are very peculiar, the labrum and the palpi—especially the maxillary palps—being well developed, while the lobes of the maxillae and labium are amalgamated and therefore indistinct. The labrum is more or less elongate, and is more mobile than is usual in mandibulate Insects; it is held closely applied to the maxillae. These latter are small, have usually only a single small free lobe; they are united to one another and to the labium by membrane in such a manner as to form a channel along the middle of the mouth, the labrum forming the roof of this channel. The palpi are in some cases (Sericostomatides) of a remarkable nature; their joints vary in number from three to five, and differ sometimes in the sexes of the same species. The lower lip appears as a plate supporting the labial palpi, which are three-jointed and do not exhibit any peculiarities of structure comparable with those we have mentioned as so frequently existing in the maxillary palps. Difference of opinion exists as to the mandibles, some entomologists declaring them to be entirely absent, while others state that a small tubercular process that may be seen in some species on each side of the labrum is their representative. The prothorax is very small, the notum is the largest piece but is quite short, the side-pieces are very small, and the sternum appears to consist only of membrane. The mesothorax is much the largest segment of the body; its sternum {475}is large, but is nearly perpendicular in direction, and is much concealed by the elongate, free front coxae, which repose against it. The metathorax is intermediate in size between the pro- and meso-thorax; its side-pieces are rather large, but the sternum is membranous, with a heart-shaped piece of more chitinous consistence in the middle, entirely covered by the middle coxae. The side-pieces both of the meso- and meta-thorax are large, and are closely connected; the middle and posterior coxae are very large, elongate, and prominent, and the middle pair slope backwards, so that their tips are in contact with the tips of the hind pair. The abdomen is cylindric and rather slender; it looks as if formed of eight segments in addition to the terminal segment; this latter in the male usually bears remarkably modified appendages. The first ventral plate is sometimes, if not always, entirely membranous; indeed the texture of the segments is in general very delicate, so that they shrivel up to an extent that renders their comprehension from dried specimens very difficult. The legs are always elongate, the coxae attaining in some forms a remarkable length, and the tibiae and tarsi are armed with many spines; the tarsi are five-jointed, slender, frequently very elongate, terminated by two large claws and an apparatus, placed between them, consisting of a pair of hair-like processes with a membranous lobe.

The structure of the mouth-parts of the Phryganeidae has given rise to much difference of interpretation; it has recently been investigated by R. Lucas[401] in connexion with _Anabolia furcata_ (Fig. 321). He agrees with other observers that mandibles are present in the pupa, but states that no rudiment of them exists in the imago. He calls the peculiar structure formed by the combination of the maxillae and {476}labium a haustellum. He looks on the Trichoptera as possessing a mouth intermediate between the biting and sucking types of Insect-mouths. He considers that the Phryganeidae take food of a solid, as well as of a liquid, nature by means of the haustellum, but the solid matter must be in the form of small particles, and then is probably sucked up by the help of saliva added to it. Lucas says also that in the larvae certain parts of the salivary glands serve the function of spinning organs, and it is from these that the salivary glands of the imago are formed; those salivary glands of the larva that are not spinning glands disappearing entirely.

The eggs are deposited in a singular manner; they are extruded in a mass surrounded by jelly; there may be as many as one hundred eggs in such a mass. This is sometimes carried about by the female after its extrusion from the interior of the body, but is finally confided to a suitable place in stream, spring, or pool. It is said that the female occasionally descends into the water to affix the egg-mass to some object therein, but this requires confirmation, and it is more probable that the egg-mass is merely dropped in a suitable situation. As soon as the larvae are hatched they begin to provide themselves with cases; they select small pieces of such material as may be at hand in the water, and connect them together by means of silk spun from the mouth. Particulars as to these tubes we will defer till we have considered the larvae themselves. These have the general appearance of caterpillars of moths; in order to move about they must put their head and the three pairs of legs at the front of the body out of their tube or case, and they then look very like case-bearing caterpillars. The part of the body that usually remains under cover is different in texture and colour, and frequently bears outstanding processes, or filaments, containing tracheae for the purpose of extracting air from the water. Some peculiar spaces of a {477}different texture may be seen on certain larvae (Fig. 322, B); these may possibly be also connected with respiration. On each side of the extremity of the body there is a rather large hook by which the creature attaches its dwelling to its body, and there are also frequently present three large bosses on the anterior abdominal segment, which are supposed to assist towards the same end. The hold it thus obtains is so firm that it cannot be dragged out by pulling from the front; fishermen have, however, discovered a way of extracting it by a strategic operation: the cases are, as a rule, partially open behind, and by putting a blunt object in and annoying the larva it is induced to relax the hold of its hooks and advance forwards in the case, or even to leave it altogether. The firm hold of the larva is maintained in spite of the fact that the body does not fill the case. It is necessary that water should pass freely into and out of the case, and that there should be some space for the respiratory filaments to move in. The mouth of the case is open, and the posterior extremity is arranged by the larva in such manner as to allow a passage for the water; various ingenious devices are adopted by different species of larvae with the object of protecting the hind end of the body, and at the same time of permitting water to pass through the case.

The mode of changing the skin, or the frequency with which this occurs in the larval state of the caddis flies has not been recorded. The duration of life in this stage is usually considerable, extending over several months: indeed in our climate many species pass the winter in this stage, completing the metamorphosis in the following spring or summer; and as one generation each year appears to be the rule, it may be assumed that the larval condition in such cases lasts from seven to ten months. During this stage the Insects are chiefly vegetable feeders, some being said to feed on minute algae; animal diet is not, however, entirely avoided, and it is said by Pictet that not only do some of the Phryganeidae eat other Insects, but that they also sometimes devour their companions.

{478}At the end of the larval period of existence the creature closes its case by a light web spun at each end, taking care not to prevent the ingress and egress of the water; it sometimes adds a stone or piece of stick, and having thus protected itself, changes to a nymph. During the first part of this metamorphosis the creature is completely helpless, for there is so great a difference between the external structures of the larva and nymph as to make the latter a new being, so far as these organs are concerned. The changes take place in the interior of the larval skin, and as they are completed this latter is shed piecemeal. The resulting pupa or nymph greatly resembles the perfect Insect, differing consequently very much from the larva. Pictet, who paid special attention to the nymph condition of these Insects, concludes, however, that many of the organs of the nymph are actually formed within the corresponding parts of the larva, and has given a figure that, if trustworthy, shows that the legs of the nymph, notwithstanding the great difference between them as they exist in the larva and in the perfect Insect, are actually formed within the legs of the larva; each nymphal leg being rolled up in the skin of the corresponding larval leg, in a spiral, compressed manner, and the only articulations that can be detected in the leg being those of the tarsus. The head of the nymph is armed in front with two curious projections that are, in fact, enormously developed mandibles (Fig. 323, B); they serve as cutting implements to enable the nymph to effect its escape from its prison; they are cast off with the nymph-skin, the perfect Insect being thus destitute of these organs. The abdomen of the nymph differs from that of the perfect Insect in possessing external respiratory filaments; the nymphs of some species have also the middle legs provided with swimming-hairs, that do not exist in the imago.

As a rule the larvae bring the respiratory filaments into contact with the water by moving the abdomen, but Fritz Müller found[402] that those of a _Macronema_ move the gills themselves—after the manner of Ephemeridae—with much rapidity. Many kinds of larvae of Phryganeids possess at the posterior extremity of the body exsertile pouches in the form of finger-like, or even branched, processes into which tracheae do not enter. Müller observed that in the _Macronema_ alluded to these pouches were generally not {479}exserted; when, however, the larva ceased to move the tracheal gills, then these pouches were protruded. He is inclined to consider them blood-gills. Similar structures are found in _Eristalis_ and some other Dipterous larvae that have to breathe under difficulties.

The imagines of certain species possess filaments—or something of the sort—on the abdomen. Palmén, who has examined these organs in _Hydropsyche_, thinks that they are the remains of gills that existed in the larva and pupa, and that they are functionless in the imaginal instar. M‘Lachlan thinks that in _Diplectrona_, where the filaments are elongate, they may be functionally active even in the imago.[403]

The skin of the nymph is at first very soft, but it soon hardens, and when about fifteen or twenty days have elapsed the nymph opens its case by means of the mandibular processes, and swims through the water with its back downwards till it reaches some solid object by which it can ascend to the air; the nymph skin then swells and splits, and the thorax of the imago protrudes; this is soon followed by the disengagement of the head and other parts, and the imago having thus escaped, the nymph skin remains a complete model of the external structure of the nymph, and contains a considerable number of tracheae. This sketch of the metamorphosis of a caddis-fly does not apply in all its details to all the forms of caddis-flies, there being exceptions, as we shall mention hereafter.

Dewitz has described[404] the first appearance and development of the wings in larvae of Phryganeidae. Each one appears at first in the form of a small thickening of the hypodermis, accompanied outwardly by a minute depression of the chitin (Fig. 324, A). He compares the structure in the earliest stage to the entothoracic projections into the interior of the body. The rudiment grows as the larva increases in size, the chitinous portion being duly shed at the ecdyses. When the rudiment is larger and more complex, a mesoderm layer appears in it (Fig. 324, B); this is derived from a nerve-sheath near the rudiment. During the resting state of the larva—after its case has been closed, but before the pupal form has appeared—the wing assumes the form and position shown in C, Fig. 324. Dewitz's description of the process leaves much to be desired, and it is doubtful whether in {480}C the position of the wing on the exterior of the body is due to the stripping off of the chitinous integument, or to a process of eversion, or to both.

There are about 500 species of this family of Insects known as inhabiting the European region, and about 150 of this number occur in Britain. These are arranged by M‘Lachlan[405]—whose zealous and persevering work at this neglected family of Insects is beyond praise—in eight sub-families, on a system in which the structure of the maxillary palpi plays a principal part; they are called Phryganeides, Limnophilides, Sericostomatides, Leptocerides, Oestropsides, Hydropsychides, Rhyacophilides, Hydroptilides. The first three of these form the division "Inaequipalpia."

PHRYGANEIDES.—This group includes the largest forms of the family, and appears to be almost confined to the temperate regions of the northern hemisphere, though a few species are already known from the corresponding districts of the southern hemisphere. This feature in their geographical {481}distribution is, however, by no means peculiar to them, for a similar discontinuity of distribution exists in numerous other groups of Insects, and even in other divisions of the Phryganeidae.

The Phryganeides almost without exception inhabit still waters, and it is more specially to them that the brief sketch of metamorphosis given in the preceding pages will be found to apply. The larva always has the respiratory filaments simple and thread-like, though elongate, and lives in a case that it carries about; this case is open at both ends, and the larva is said to occasionally cut off the end having the least diameter and increase the other end, thus accommodating the habitation to its own growth.

LIMNOPHILIDES.—These Insects have only three, instead of four, joints in the maxillary palpi, but in most other respects agree with the Phryganeides. There is, however, greater variety in the habits of the larvae, though all live in free cases. In the genus _Enoicyla_ (Fig. 326) we meet with the anomaly of a Trichopterous Insect that lives amongst moss and dead leaves, far away, it may be, from water. The cases of the Limnophilides are constructed of a great variety of materials, and are often decorated with shells containing living inmates.

In the genus _Apatania_ the phenomenon of parthenogenesis is thought to occur, there being at least two species in which no male specimen has ever been discovered, though M‘Lachlan has made special efforts to discover the sex of _A. muliebris_. It should, however, be stated that these species have not been extensively investigated; _A. arctica_ has been detected in the Arctic regions, and _A. muliebris_ has occurred in several localities in Europe, in Britain chiefly near Arundel in a lake of intensely cold water.

{482}SERICOSTOMATIDES, like the Limnophilides, is a group rich in species; the larvae are chiefly found in streams. They form portable cases out of sand and stones (Fig. 325, B, case of _Crunoecia irrorata_) in preference to vegetable matter. It is here that the genus _Helicopsyche_, which for long was an enigma to naturalists, is now placed. This genus consists of Insects whose larvae form spiral cases, similar to small snail shells, of sand or minute stones. These objects occur in various parts of the world. Fritz Müller[406] has informed us that the larva inhabiting one of them, when it withdraws entirely within its abode to repose, takes the precaution of anchoring its snail-like habitation, fixing it to a rock or stone by spinning some temporary silken threads. The respiratory filaments in this group are filiform.

LEPTOCERIDES.—The first group of the division Aequipalpia; so that there are five-jointed maxillary palpi in both sexes; these organs are frequently developed in a remarkable manner. The antennae are usually extremely long and slender. The case of the larva is portable (Fig. 325, A, case of _Odontocerum_); the respiratory filaments are not very conspicuous; they form short tufts placed on various parts of the abdomen. Müller[406] has called attention to a species whose larva lives in Brazil between the leaves of Bromeliae on trees.

The OESTROPSIDES is a small group, and has recently been reduced by M‘Lachlan to the rank of an inferior division.

HYDROPSYCHIDES.—An extensive group, in which the larvae are believed to be chiefly of carnivorous habits. They vary, according to species, as to the nature of the respiratory filaments, and live in fixed abodes; these are less tubular than is the rule with the portable cases, and are formed from pieces of sand and stone spun together and fixed to larger stones under water. Sometimes several larvae live together in loosely compacted structures of this kind, and only form true cases when about to undergo their metamorphosis. Müller describes[406] a Brazilian species of _Rhyacophylax_ as forming a case in which the mouth-end has a {483}large funnel-shaped verandah, covered by a beautiful silken net. This larva lives in the rapids of various rivulets, and the entrance to the verandah is invariably directed towards the upper part of the rivulet, so as to intercept any edible material brought down by the water. Several of these larvae, moreover, build their cases so that they form a transverse row on the upper side of a stone; as many as thirty cases may be placed in one of these rows, and sometimes several rows are placed parallel with one another. This same larva has the habit of coming out of its case when necessary, and suspending itself in the water—as some caterpillars do in the air—by means of a silken thread. Other members of the Hydropsychides form tubes or covered ways of silk, earth and mud attached to stones, and in which they can move freely about. Some of the Hydropsychidae have been ascertained with certainty to be carnivorous in the larval state. A species of the genus _Hydropsyche_ has been found by Howard[407] to help itself in the task of procuring food by spreading a net in the water in connexion with the mouth of its case. This net is woven in wide meshes with extremely strong silk, and supported at the sides and top by bits of twigs and small portions of the stems of water-plants. Small larvae brought down by the current are arrested by this net for the advantage of the larva that lurks in the tube. The breathing organs of the larvae of Hydropsychides are apparently of a varied character, and would well repay a careful study. Mr. Morton informs the writer that some of our British species of _Philopotamus_ and _Tinodes_ have no gills either in the larval or pupal state, and probably respire by means of modified tracts in the integument. In some of the allied genera, _e.g._ _Polycentropus_, the larvae are destitute of gills, but the pupae possess them.

The RHYACOPHILIDES is another group in which the larval habitations are fixed. Some of these larvae have no respiratory filaments, breathing only by means of the stigmata, but others have tufts of filaments. These Insects have a peculiarity in their {484}metamorphosis inasmuch as the larva, instead of lying free, constructs a cocoon in its case or other habitation in which to change to a nymph. In the larvae that do not make use of a portable case the abdominal hooks are not essential, and are replaced by other organs differing much in structure, being sometimes apparently of a sensitive nature, in other forms possibly respiratory. Müller tells us of a carnivorous larva of this group in which the anterior legs are armed with powerful forceps for predatory purposes.

The HYDROPTILIDES comprise the most minute of the Phryganeidae, and their species will probably prove to be very numerous in well-watered tropical regions, though few have yet been described from there. The perfect Insects (Fig. 320) bear an extreme resemblance to small moths of the group Tineidae. The larvae (Fig. 329) are destitute of respiratory filaments, and construct portable cases of a variety of forms, some resembling seeds. Müller has given particulars of a curious nature as to the cases of some Brazilian Hydroptilides; one species moors its dwelling to a stone by means of a long silken cable, by this artifice combining safety with the power of ranging over a considerable extent of water. In _Diaulus_ there is only a narrow slit at each end of the case, but one side of it is provided with two chimneys to permit the flow of water for respiratory purposes.

The larva of _Oxyethira_ (Fig. 330) is a curious form, possessing comparatively long legs, and a head and thorax slender in comparison with the distended hind body. The cases are fastened, for the purposes of pupation, to a leaf of a water-lily.

Some very curious anomalies as regards the development of the wings exist in the Phryganeidae; _Anomalopteryx_, for instance, has the wings quite short and useless for flight in the male, while in the other sex they are ample; in _Enoicyla_—the curious Insect figured on p. 481, in which the larvae are of terrestrial habits—we find the females with only rudiments {485}of wings, while in _Thamastes_ the posterior wings are absent in both sexes. These anomalies are at present quite inexplicable; and we may here mention that we are in complete ignorance as to the functional importance of many of the peculiarities of the Phryganeidae. We do not know why the mouth is reduced from the normal state, the maxillary palpi being, on the other hand, extraordinarily developed; we do not know the importance of the numerous spines and of the spurs on the legs, nor of the hairs on the wings, although these are amongst the most characteristic of the special features of this group of Insects.