Part 33

In the perfect state, as well as in that of the larva and the pupa, the _Libellulæ_ are carnivorous. Their rapid flight makes them expert hunters, and their enormous eyes embrace the whole horizon. They seize, while on the wing, flies and butterflies, and tear them to pieces immediately with their strong mandibles. Sometimes, the ardour of the chase leading them on far from the streams, they are met with in the fields. The female lays her eggs in the water, from which emerge larvæ which remind one somewhat of the form of the insect, only their body is more compact and their head flattened. The larvæ and pupæ inhabit the bottom of ponds and streams, where, keeping out of sight in the mud, they seek for insects, molluscs, small fish, &c. If any prey passes within their reach, they dart forward, like a spring, a very singular arm, which represents the under lip. It is a sort of animated mask, armed with strong jagged pincers and supported by strong joints, the which, taken together, is equal to the length of the body itself. This mask acts at the same time as a lip and an arm; it seizes the prey on its passage, and conveys it to the mouth. "When any aquatic insect approaches them at a time when they are in a humour for eating," says Charles de Geer, "they shoot the mask forward very suddenly and like a flash of lightning, and seize the insect between their two pincers; then, drawing back the mask, they bring the prey up to their mandibles, and begin to eat it. I have remarked that they do not spare those of their own kind, but that they eat each other up when they can, and I have also seen them devouring very small fish which I put by them. It is very difficult for other insects to avoid their blows, because, walking along generally in the water very gently, and, as it were, with measured steps--almost in the same way a cat does on the look-out for birds--they suddenly dart forward their mask and seize their prey instantaneously."[118] Fig. 394 represents, to the left, the larva of the dragon-fly, with the instrument of attack which we have called a "mask," and which it is making use of for seizing a small insect; on the right, the adult dragon-fly coming out of the nymph.

[118] Charles de Geer, "Mémoires pour servir à l'Histoire des Insectes," tome ii., 2e partie, p. 674.

The respiration of these larvæ is very singular. Their abdomen is terminated by appendages, which they open to allow the water to penetrate into the digestive tube, the sides of which are furnished with gills communicating with the tracheæ. The water, deprived of oxygen, is then thrown out, and the larva advances thus in the water by the recoil. It has no tufts of external lateral gills, which in the case of the _Ephemeræ_ do the duty of fins. The pupa already presents stumps of wings. To effect its metamorphosis it drags itself out of the water, where it has lived for nearly a year, climbs slowly to some neighbouring plant, and hangs itself there. Very soon the sun dries and hardens its skin, which all of a sudden becomes crisp, and cracks. The dragon-fly then sets free its head and its thorax, and its legs; its wings, still soft and wanting in vigour, gain strength by coming in contact with the air, and, after a few hours, they have attained their full development. Immediately the insect abandons, like a worn-out suit, the dull slimy skin which had covered it so long, and which still preserves its shape (Fig. 394), and dashes off in quest of prey.

The _Libellulas_ are common all over the world. Their type is the _Libellula depressa_ (Fig. 395), very common in Europe. The male is brown, with the abdomen blue underneath; the female, of a sort of olive-yellow, bordered by yellow on the sides. Both have the abdomen broad and flattened.

The _Æshna_, with a cylindrical abdomen, attains to the length of two and a half inches. Its flight is more rapid than that of the swallow. The _Calepteryx_ flies more slowly. The male is of a metallic blue, its diaphanous wings are traversed by a band of greenish blue; the female, of a bronzed green, has wings of a metallic green, with a yellowish mark on the edge. These insects rest on reeds, retaining their wings in a vertical position.

The _Agrions_, which are of the same family, have the body white, brown, or green, and the eyes very prominent. They are more slim and graceful than the _Libellulas_, properly so called; their larva are very elongated.

In the spring, one meets in the woods with insects having large heads and elongated thoraces. The females have a long auger, with which to deposit their eggs under the bark of trees, where their larvæ, which feed on insects, and twist themselves about like small serpents, live. The pupæ are also very active; they resemble the adults very much, and have the wings laid against the body. These insects, which are met with everywhere, but always in small numbers, are the _Raphidias_, which we see represented (Figs. 396, 397, 398) in the state of larva, pupa, and adult, and the _Mantispas_ (Fig. 399), one species of which is common in the south of Europe.

M. Blanchard classes in the same tribe the genus _Semblis_, whose larvæ are aquatic, with scaly heads, provided with eyes, and with curved mandibles and short antennæ. The larvæ and the pupæ breathe, like those of the _Ephemeræ_, by articulated external processes, or gills, analogous to those of fishes. Nevertheless the pupæ live on land, not in water. They hide themselves in the earth at the foot of trees, and the adult issues forth at the end of a fortnight, leaving its pupa skin behind. It lives but a few days. The female lays her eggs on reeds, stones, &c. Fig. 400 represents the Mud _Semblis_ in its three states.

We now come to those Neuroptera which undergo complete metamorphoses. They are the Myrmeleonidæ, of which the Ant-lion (_Myrmeleo_) is the most prominent type, and the _Phryganidæ_, or Caddis Flies.

The larvæ of the Ant-lions live on the land, and are carnivorous. When about to undergo their transformation into pupæ, they spin for themselves a silky cocoon. The larvæ of the _Phryganeas_, on the contrary, live in the water. They surround themselves with a sort of protecting case, composed of a silky shell and incrustations of all sorts. The pupæ, as well as the larvæ of these insects, breathe by means of gills.

The Ant-lion (_Myrmeleo formicarius_, Fig. 401) is found in the environs of Paris. It is an elegant insect, resembling the dragon-fly, but is distinguished from it by its antennæ. Its larva is of a rosy, rather dirty grey, with little tufts of blackish hair on its very voluminous abdomen. Its legs are rather long and slender; the two anterior pair of legs are directed forwards, whilst the hind legs are fixed against the body, and only permit the animal to walk backwards. These larvæ are met with in great abundance in sandy places very much exposed to the heat of the sun. There they construct for themselves a sort of funnel in the sand (Fig. 402), by describing, backwards, the turns of a spiral whose diameter gradually diminishes. Their strong square head serves them as a spade with which to throw the sand far away: they then hide themselves at the bottom of the hole, their head alone being out, and wait with patience for some insect to come near. Scarcely has the ant-lion perceived its victim on the borders of its funnel, when it throws at it a shower of dust to alarm it, and make it fall to the bottom of the precipice, which does not fail to happen. Then it seizes it with its sharp mandibles, and sucks its blood; after which it throws its empty skin out of the hole and resumes the look-out. Ants especially become its prey, whence its name of Ant-lion. Towards the month of July, the larvæ make themselves a spherical cocoon, mixed with grains of sand, in which they are transformed into pupæ which are hatched towards the end of August. The perfect ant-lions diffuse an odour of roses; their flight, which is weak, distinguishes them from the dragon-flies. We meet in the south of France with a very beautiful species of Ant-lion, the _Myrmeleo libelluloides_ (Fig. 404); its larva can move forwards, and does not dig itself a funnel.

The genus _Ascalaphus_ (Fig. 407) is remarkable for the long clubbed antennæ of its members, and for their rapid flight. They like the sun, and live especially in hot countries; however, one meets with the _Ascalaphus_, in the month of July, near Paris, on the dry declivities of Lardy and of Poquency. Their larvæ (Fig. 406) have mandibles adapted for suction. They watch for insects under heaps of stones, and spring upon their prey.

The first states of the _Nemoptera_[119] (Fig. 408) are as yet little known. They are insects with wings spotted with yellow and black, the lower ones almost linear, and are met with in southern countries, and but very rarely in the south of France.

[119] From [Greek: nêma], a thread, and [Greek: pteron], a wing.

The _Hemerobii_, to which are given by the French the name of _Demoiselles terrestres_, or Land Dragon-Flies, are very small delicate insects, of an apple-green colour, with golden red eyes. These insects leave on the fingers, when seized, an offensive odour. Réaumur calls them _Lions des pucerons_ (Plant-Lice Lions), because their larvæ, which resembles the larvæ of the ant-lions, and which live on plants, feed on plant-lice. They attack also caterpillars. Their mandibles are provided with a canal for suction, like those of the foregoing species.

The insects of the genus _Osmylus_ (Fig. 409) are rather rare; but may be found in the shrubs which border ponds. They also belong to the _Hemerobidæ_. Their larvæ live in wet ground.

The _Panorpatæ_ constitute a singular little family, having a peculiar shaped head, which is prolonged to a sort of long and slender beak. Aristotle called them Scorpion Flies, and thought they were winged scorpions. The _Panorpas_, properly so called (Fig. 410), are found on hedges and plants during the summer. They have slim bodies spotted with yellow and black, and four straight wings, also spotted with black. In the males the abdomen terminates in a pair of pincers (Fig. 411), which rather remind one of the tail of a scorpion, and which are destined to seize their prey, which they kill by piercing with their beak. The female lays her eggs in the ground (Fig. 412). In a week the larva makes its appearance; it is a month in developing, it then buries itself still deeper in the earth, and changes into a pupa, which, after a fortnight, comes again into the light in the form of a perfect insect. There are two other genera of _Panorpatæ_, of which _Bittacus tipularis_ (Fig. 413), resembling a large gnat, furnished with four wings, and _Boreus hyemalis_ (Fig. 414), of a brilliant black, met with in Sweden and in the elevated parts of the Alps, jumping about on the snow in considerable troops--are representatives. The latter has been found in England.

The _Phryganidæ_, or Caddis Flies, are known by their larvæ, of which anglers make great use. Réaumur classed them as aquatic moths. The soft and delicate body of the larvæ is protected by a case, to which they cling by two hooks, placed at the extremity of their abdomen. They are called by different names in allusion to their habits; as, for instance, case worms, from their living in a case covered with little bits of wood or sand, which they draw after them as they go. Their scientific name, _Phryganea_, signifies _fagot_.[120] The _Phryganeæ_, in the adult state, very much resemble moths. They approach them in having rudimentary mouths, and wings without articulations, but furnished with small hairs, analogous to the scales of Lepidoptera. They may be said to form a sort of connection between the Lepidoptera and Neuroptera. They have been called _Mouches papilionacées_, or Papilionaceous Flies. The eggs laid by the female _Phryganea_ are enclosed in gelatinous capsules, which swell in the water and attach themselves to stones, &c. The larva has the appearance of a little worm without feet. It is soon hatched, and resembles at first a little black line, and may be easily reared in an aquarium. The operation of making the silky case which it draws after it, and which protects its abdomen, may then be observed. When it is disturbed, it retreats entirely within its case. The interior is smooth, and lined with mud; on the exterior it is fortified with stones, &c.

[120] From [Greek: phryganion], a stick.

The _Phryganea rhombica_ (Figs. 415, 416, 417) furnishes its case with bits of wood or grass, arranged as shown in Fig. 418. Some species arrange these bits of wood and glass in spiral, others in parallel series. The _Phryganea flavicornis_ covers its dwelling with little shells. "These kinds of dress," says Réaumur, "are very pretty, but they are also excessively singular. A savage who, instead of being covered with furs, should be covered with musk rats, moles, or other entire animals, would have on an extraordinary costume; this is in some sort the case with our larvæ." Other _Phryganeæ_ employ for constructing the case which serves them as a dwelling sand and small pebbles; each species always employing the same materials, unless they are entirely deprived of these and obliged to employ others. These cases protect the larvæ against the voracity of their enemies. The larvæ have a scaly head; and the three first rings of their body are harder than the rest. They live in water, and breathe by means of branchious sacs, arranged on the abdomen in soft and flexible tufts. They eat everything that is presented to them: leaves, and even insects and the larvæ of their own kind. The pupæ are motionless. They stay about a fortnight in their case, the orifice of which is closed by gratings of silk, then break through the gratings, and leave their prison. In this state (Fig. 419) they swim on the water until they meet with an object to which they can attach themselves, and so get out. Then they swell till they crack their skin over the back, and the perfect insect emerges.

The _Phryganea pilosa_ (Fig. 420) is of a yellowish grey, with hairy wings, little adapted for flying. These insects do not eat, and never leave the neighbourhood of the water. During the day they rest on flowers, on walls, or on the trunks of trees, their wings folded back, and their antennæ together. In the evening they fly in dense swarms over streams and ponds. They are attracted by light, as are many nocturnal insects; and are sometimes found in great numbers on the lamps on the quays in Paris.

The _Hydropsyches_ (Fig. 421) and _Rhyacophili_ (Fig. 422) are small insects which resemble the _Phryganeæ_ very closely. Their larvæ have, for the purposes of respiration, some gills, others retractile tubes. They construct for themselves fixed places of shelter, more or less imperfect, at the bottom of the water, and against large stones, which they leave occasionally for a few moments. Sometimes these cases contain several larvæ. Fig. 421 represents the various states of a _Hydropsyche_; the larva is seen on the left, the pupa on the right, the winged insect in the middle. Two of the insect's tents, or places of shelter, are represented below. Fig. 422 shows the different states of _Rhyacophilus vulgatus_, larva, cocoon, pupa, and imago. The genus _Rhyacophilus_ has this peculiarity, that the larva spins itself a cocoon in the interior of its dwelling before changing into a pupa.

IX.

COLEOPTERA.

In collections of insects the Coleoptera almost always occupy the principal place. They are sought after by collectors on account of the brightness of their colours, of the solidity of their integuments, and the facility with which they can be preserved. This circumstance has contributed much to give to the Coleopterous Order marked preponderance in the immense series of insects. Many more have been collected than any one has as yet been enabled to describe; and the collections are encumbered with species of which no naturalist has yet given an account.

Admitting that the first-rate collections contain each about 25,000 perfectly distinct species, and that a certain fraction of these treasures is peculiar to each collection, M. Blanchard came to the conclusion that we must estimate the number at more than 100,000 of the species of Coleoptera which would be obtained if the different entomological collections of France, England, and Germany were put together. But every day we see arriving from different regions of the globe new riches, hardly dreamt of up to that time; and it is not only the small species, but the larger and more beautiful also, which furnish their contingent. It may, then, be believed that, if the entire surface of the earth were carefully explored, we should obtain an incalculable number of Coleoptera, having sufficient characteristics to constitute distinct species or kinds.

The Coleoptera (from [Greek: koleos], a sheath, and [Greek: pteron], a wing) are insects with four wings. The anterior wings, or _elytra_, are not used in flying; they are sheaths, more or less hard, sometimes varied with bright colours, and never crossing over each other. The posterior wings are membranous, presenting a ramification of veins, and usually folding up under the _elytra_, which protect them when at rest. The mouth of Coleoptera is provided with mandibles, with jaws, and two quite distinct lips, and is suited for mastication. They undergo complete metamorphosis. After an existence of greater or less extent in the larva state (in the case of the cockchafer three years), the insect changes into a pupa, which remains in a state of complete immobility. After a certain time, the pupa bursts its envelope and assumes the form of a perfect insect. The Coleoptera presents the utmost variety of habits as regards their habitations and food. One does not find in this Order those admirable instincts, those manifestations of intelligence, which bring certain Hymenoptera near to those beings which are highest in the animal scale; but they offer peculiarities very well deserving serious and profound study. Some are carnivorous, and thus they are useful to man in destroying other noxious insects, which they seek on the ground, on low plants, on trees, and even in the depths of the waters. Many of these Coleoptera feed on animal matter in a state of putrefaction. We may look on them as useful auxiliaries: they are Nature's undertakers.

A great number live in the excrements of animals. The dung of oxen, buffaloes, and camels afford shelter to Coleoptera of different families, which thus live on vegetable matter more or less animalised. Others attack skins and dried animals in general; and some are the pest of entomological collections. Lastly, immense legions of Coleoptera are phytophagous; that is to say, they attack roots, bark, wood, leaves, and fruits, and cause much annoyance to the agriculturist. Above all, the larvæ are to be dreaded. Those which live in wood may in a few years occasion the loss of trees, vigorous and full of life; or completely destroy the beams of a building. Certain larvæ, such as those of the cockchafer, eat away the roots of vegetables, and so destroy the harvests. Others, lastly, devour the leaves and the stalks of plants, attack the flowers in the gardens, or the corn in the barns; and so man makes desperate war against them.

In the immense variety of known Coleoptera we must be contented to choose those types which are most prominent and most characteristic. We will begin with the _Scarabæides_, with their heavy compact body, and short antennæ, terminated by a foliaceous club. It is to this tribe that belongs the beautiful Rose Beetle (_Cetonia aurata_), which lives on roses; the Cockchafer (_Melolontha vulgaris_); the _Scarabæus_ of the Egyptians; &c.

This is the most interesting tribe of the whole Order Coleoptera. It corresponds with the great division of the _Lamellicornes_ of Latreille. This name of _Lamellicornes_ was intended to remind us of the arrangement into laminæ, more or less close together, of the club of the antennæ of these insects. Many _Scarabæi_ have their mandibles membranous, or at least partially so, and always small. This peculiarity corresponds to their habits. Never, indeed, have they to triturate hard bodies; they all feed either on flowers, on leaves, or on stercoraceous matter. Their larvæ resemble each other much, even those of families very widely differing from each other in the perfect state. They are large, whitish worms, with diaphanous skins, scaly heads, furnished with toothed mandibles, living in the ground or in rotten wood. The pupæ are fat and stumpy, and they already show the features of the perfect insect. They make a chamber in which to undergo their changes. They remain generally three years in the larva state. The duration of the pupa is very short, as also is that of the perfect insect. The differences of the sexes are often very marked on the exterior, by protuberances, horns, &c., which constitute the distinctive ornament of the males.

In the group of _Scarabæides_ we shall have to speak, above all, of the _Cetoniadæ_, the Chafers, and the _Scarabæi_ properly so called. The family _Cetoniadæ_ is one of the most remarkable, on account of the beauty of the insects which compose it and of the richness of their metallic lustre, some being of great splendour, and others having velvety tints. The larvæ live in wood in a state of decomposition; the perfect insects frequent flowers, and like the sun.