Part 1

Transcriber Note

Emphasized text represented as _Italic_. Whole and fractional part of numbers: 1-3/4.

THE

INSECT WORLD:

BEING

_A Popular Account of the Orders of Insects_;

TOGETHER WITH

A DESCRIPTION OF THE HABITS AND ECONOMY OF SOME OF THE MOST INTERESTING SPECIES.

BY LOUIS FIGUIER.

A New Edition,

REVISED AND CORRECTED BY P. MARTIN DUNCAN, F.R.S.

WITH 579 ILLUSTRATIONS.

D. APPLETON AND CO., _NEW YORK_.

PREFACE

This popular French book on Insects has been placed in my hands in order that the scientific portions of it should be examined and, if necessary, corrected. This task has been a light one, for the book had already passed through the able editorship of Mr. Jansen. But I have added a short notice of the Thysanoptera, which did not appear in M. Figuier's original work, and also the necessary information respecting the evolution of Stylops.

P. MARTIN DUNCAN. LEE, 1872.

CONTENTS.

PAGE INTRODUCTION 1 APTERA 27 DIPTERA 33 Nemocera 35 Brachycera 47 HEMIPTERA 90 Heteroptera 90 Homoptera 101 LEPIDOPTERA 138 The Larva, or Caterpillar 138 The Chrysalis, or Pupa 146 The Perfect Insect 165 ORTHOPTERA 284 HYMENOPTERA 313 THYSANOPTERA 400 NEUROPTERA 402 COLEOPTERA 435 INDEX 523

THE INSECT WORLD.

INTRODUCTION.

It is not intended to investigate the anatomy of insects in this work thoroughly; but, as we are about to treat of the habits and economy of certain created beings, it is necessary first to explain the principal parts of their structure, and the stages which every perfect insect or _imago_ has undergone before arriving at that state.

We, therefore, proceed to explain, as simply as possible, the anatomy of an insect, and the functions of its organs.

If we take an insect, and turn it over, and examine it carefully, the first thing that strikes us is that it is divided into three parts: the head; the thorax, or chest; and the abdomen, or stomach.

The head (Fig. 1) is a kind of box, formed of a single piece, having here and there joints more or less strongly marked, sometimes scarcely visible. It is furnished in front with an opening--often very small--which is the mouth; and with some for the eyes, and with others for the insertion of the antennæ or horns.

The integuments of the head are generally harder than the other parts of the body. It is necessary that this should be so. Insects often live and die in the midst of substances which offer some resistance. It is necessary, therefore, that the head should be strong enough to overcome such resistance. The head contains the masticatory organs, which, frequently having to attack hard substances, must be strongly supported. The exception to this rule is among insects which live by suction.

It would be out of place here to mention the numerous modifications of the head which are presented in the immense class of insects.

The eyes of insects are of two kinds. There are compound eyes, or eyes composed of many lenses, united by their margins and forming hexagonal facettes; and there are also simple eyes, or ocelli.

The exterior of the eye is called the cornea (Fig. 2), each facette being a cornea; and the facettes, which vary in size even in the same eye, unite and form a common cornea, which is represented by the entire figure.

In order to show the immense number of the facettes possessed by many insects, we give the following list:--

In the genus Mordella (a genus of beetles) the eye has 25,008 facettes. In the _Libellula_ (dragon-fly) 12,544 " In the genus _Papilio_ (a genus of butterflies) 17,355 " In _Sphinx convolvuli_ (the convolvulus hawk-moth) 1,300 " In _Bombyx mori_ (the common silkworm moth) 6,236 " In the house-fly 4,000 " In the ant 50 " In the cockchafer 8,820 "

The facettes appear to be most numerous in insects of the genus _Scarabæus_ (a genus of beetles). They are so minute, that they can only be detected with a magnifying glass.

Looked at in front, a compound eye may be considered an agglomeration of simple eyes; but internally this is hardly correct.

On the under side of each facette we find a body of a gelatinous appearance, transparent, and usually conical; the base of this occupies the centre of the facette in such a manner as to leave around it a ring to receive some colouring matter. This body diminishes in thickness towards its other extremity, and terminates in a point where it joins a nervous filament proceeding from the optic nerve. These cones, agreeing in number with the facettes, play the part of the crystalline lens in the eyes of animals. They are straight and parallel with each other. A pigment fills all the spaces between the cones, and between the nervous filaments, and covers the under side of each cornea, except at the centre. This pigment varies much in colour. There are almost always two layers, of which the exterior one is the more brilliant. In fact, these eyes often sparkle with fire, like precious stones.

M. Lacordaire, in his "Introduction à l'Entomologie," from which we borrow the greater part of this information, has summed up as follows, the manner in which, according to M. Müller, the visual organs of insects operate:--

"Each facette, with its lens and nervous filament, separated from those surrounding them by the pigment in which they are enclosed, form an isolated apparatus, impenetrable to all rays of light, except those which fall perpendicularly on the centre of the facette, which alone is devoid of pigment. All rays falling obliquely are absorbed by that pigment which surrounds the gelatinous cone. It results partly from this, and partly from the immobility of the eye, that the field of vision of each facette is very limited, and that there are as many objects reflected on the optic filaments as there are corneæ. The extent, then, of the field of vision will be determined, not by the diameter of these last, but by the diameter of the entire eye, and will be in proportion to its size and convexity. But whatever may be the size of the eyes, like their fields of vision, they are independent of each other; there is always a space, greater or less, between them; and the insect cannot see objects in front of this space without turning its head. What a peculiar sensation must result from the multiplicity of images on the optic filaments! This is not more easily explained than that which happens with animals which, having two eyes, see only one image; and probably the same is the case with insects. But these eyes usually look in opposite directions, and should see two images, as in the chameleon, whose eyes move independently of each other. The clearness and length of vision will depend, continues M. Müller, on the diameter of the sphere of which the entire eye forms a segment, on the number and size of the facettes, and the length of the cones or lenses. The larger each facette, taken separately, and the more brilliant the pigment placed between the lenses, the more distinct will be the image of objects at a distance, and the less distinct that of objects near. With the latter the luminous rays diverge considerably; while those from the former are more parallel. In the first case, in traversing the pigment, they impinge obliquely on the crystalline, and consequently confuse the vision; in the second, they fall more perpendicularly on each facette.

"Objects do not appear of the same size to each optic filament, unless the eye is a perfect section of a sphere, and its convexity concentric with that of the optic nerve. Whenever it is otherwise, the image corresponds more or less imperfectly with the size of the object, and is more or less incorrect. Hence it follows, that elliptical or conical eyes, which one generally finds among insects, are less perfect than those referred to above.

"The differences which exist in the organisation of the eye among insects are explicable, to a certain point, on the theory which we are about to explain in a few words. Those species which live in the same substances on which they feed, and those which are parasitical, have small and flattened eyes; those, on the contrary, which have to seek their food, and which need to see objects at a distance, have large or very convex eyes. For the same reason the males, which have to seek their females, have larger eyes than the latter. The position of the eyes depends also on their size and shape; those which are flat, and have consequently a short field of vision, are placed close together, and rather in front than at the sides of the head, and often adjoining. Spherical and convex eyes, on the contrary, are placed on the sides, and their axes are opposite. But the greater field of vision which they are able to take in makes up for this position."

Almost all insects are provided with a pair of compound eyes, which are placed on the sides of the head. The size and form of these organs are very variable, as we shall presently see. They are generally placed behind the antennæ.

Although simple eyes (ocelli or stemmata) are common, they do not exist in all the orders of insects. They are generally round, and more or less convex and black, and there are three in the majority of cases. When there is this number they are most frequently placed in a triangle behind, and at a greater or less distance from the antennæ. Under the cornea, which varies in convexity, is found a transparent, rather hard, and nearly globular body, which is the true crystalline resting on a mass, which represents the vitreous body. This vitreous body is enclosed in an expansion of the optic nerve. Besides these, there is a pigment, most frequently red-brown, sometimes black, or blood-red. The organisation of these eyes is analogous to the eyes of fishes, and their refractive power is very great.

With these eyes insects can only see such objects as are at a short distance. Of what use then can stemmata be to insects also provided with compound eyes? It has been remarked that most insects having this arrangement of eyes feed on the pollen of plants, and it has been surmised that the stemmata enable them to distinguish the parts of the flowers.

The antennæ, commonly called horns, are two flexible appendages, of very variable form, which are joined to different parts of the head, and are always two in number. The joints of which they are made up have the power of motion, which enables the insect to move them in any direction.

The antennæ consist of three parts: the basal joint, commonly distinguished by its form, length, and colour; the club, formed by a gradual or sudden thickening of the terminal joints, of which the number, form, and size present great variations; lastly, the stalk, formed by all the joints of the antennæ, except the basal, when no club exists, and in case of the existence of a club, of all those between it and the basal one.

We give as examples the antennæ of two beetles, one of the genus _Asida_, the other of the genus _Zygia_ (Figs. 3 and 4).

Insects, for the most part, while in repose, place their antennæ on their backs, or along the sides of the head, or even on the thorax. Others are provided with cavities in which the antennæ repose either wholly or in part.

During their different movements, insects move their antennæ more or less, sometimes slowly and with regularity, at other times in all directions. Some insects impart to their antennæ a perpetual vibration. During flight they are directed in front, perpendicular to the axis of the body, or else they repose on the back.

What is the use of the antennæ, resembling as they do, feathers, saws, clubs, &c.? Everything indicates that these organs play a very important part in the life of insects, but their functions are imperfectly understood. Experience has shown that they only play a subordinate part as feelers, and have nothing to do with the senses of taste or smell. There is no other function for them to fulfil, except that of hearing.

On this hypothesis the antennæ will be the principal instruments for the transmission of sound-waves. The membrane at their base represents a trace of the tympanum which exists among the higher animals. This membrane then will have some connection with an auditory nerve.

The mouth of insects is formed after two general types, which correspond to two kinds of requirements. It is suited in the one case to break solid substances, in the other to imbibe liquids.

At first sight there seems no similarity between the mouth of a biting insect and of one living by suction. But on examination it is found that the parts of the mouth in the one are exactly analogous to the same parts in the other, and that they have only modifications suiting them to the different purposes which they have to fulfil.

The mouth of a biting insect is composed of an upper lip, a pair of mandibles, a pair of jaws, and a lower lip (Fig. 5).

The lower lip and the jaws carry on the outside certain appendages or filaments which have received the name of _palpi_.

When speaking of sucking insects, and in general of the various orders of insects, we shall speak more in detail of the various parts of the mouth.

The thorax (Fig. 6), the second primary division of the body of insects, plays almost as important a part as the head. It consists of three segments or rings, which are in general joined together--the prothorax, the mesothorax, and the metathorax, each of which bears a pair of legs. The wings are attached to the two posterior segments.

All insects have six true legs. There is no exception whatever to this rule, though some may not be developed.

From the segments to which they are attached, the legs are called anterior, posterior, and intermediate. The legs are composed of four parts: the trochanter, a short joint which unites the thigh to the body; the thigh or _femur_; the _tibia_, answering to the shank in animals; and the _tarsus_, or foot, composed of a variable number of pieces placed end to end, and called the _phalanges_.

We take as examples the hind leg of a _Heterocerus_ (Fig. 7), and the front leg of a _Zophosis_ (Fig. 8) (genera of beetles).

We shall not dwell on the different parts, as they perform functions which will occupy us later, when speaking of the various species of the great class of insects.

The functions which the legs of insects have to perform consist in walking, swimming, or jumping.

In walking, says M. Lacordaire, insects move their legs in different ways. Some move their six legs successively, or only two or three at a time without distinction, but never both legs of the same pair together, consequently one step is not the same as another. The walk of insects is sometimes very irregular, especially when the legs are long; and they often hop rather than walk. Others have one kind of step, and walk very regularly. They commence by moving the posterior and anterior legs on the same side and the intermediate ones on the opposite side. The first step made, these legs are put down, and the others raised in their turn to make a second.

Running does not change the order of the movements, it only makes them quicker--very rapid in some species, and surpassing in proportion that of all other animals; but in others the pace is slow. Some insects rather crawl than walk.

In swimming, the posterior legs play the principal part. The other legs striking the water upwards or downwards, produce an upward or downward motion. The animal changes its course at will by using the legs on one side only, in the same way as one turns a rowing boat with one oar without the aid of a rudder. Swimming differs essentially from walking, for the foot being surrounded by a resisting medium, the legs on both sides are moved at the same time.

The act of jumping is principally performed by the hind legs. Insects which jump have these legs very largely developed, as in Fig. 9. When about to jump they bring the tibia into contact with the thigh, which is often furnished with a groove to receive it, having on each side a row of spines. The leg then suddenly straightens like a spring, and the foot being placed firmly on the ground, sends the insect into the air, and at the same time propels forward. The jump is greater in proportion as the leg is longer.

To treat here in a general manner of the wings of insects would be useless. We shall refer to them at length in their proper place, when treating of the various types of winged insects.

In the perfect insect the abdomen does not carry either the wings or the legs. It is formed of nine segments, which are without appendages, with the exception of the posterior ones, which often carry small organs differing much in form and function. These are saws, probes, forceps, stings, augers, &c. We shall consider these different organs in their proper places.

With vertebrate animals, which have an interior skeleton suited to furnish points of resistance for their various movements, the skin is a more or less soft covering, uniformly diffused over the exterior of the body, and intended only to protect it against external injury. In insects the points of resistance are changed from the interior to the exterior. The skin is altered by Nature to fit it to this purpose. It is hard, and presents between the segments only membranous intervals, which allow the hard parts to move in all directions.

We are examining a perfect insect; we have glanced at its skeleton, and the different appendages which spring from it. The principal organs which are contained in the body remain to be examined.

We will first study the digestive apparatus. This apparatus consists of a lengthened tubular organ, swollen at certain points, forming more or less numerous convolutions, and provided with two distinct orifices. This alimentary canal is always situated in the median line of the body, traverses its whole length, and is at first surrounded by, and then passes above, the nervous ganglia.[1]

[1] _Ganglion_--a mass, literally a knot, of nervous matter.

In its most complicated form the alimentary canal is composed of an _oesophagus_, or gullet, of a crop, of a gizzard, of a chylific ventricle or stomach, a small intestine, a large intestine, divers appendages, salivary, biliary, and urinary glands. The oesophagus is often not wider than a hair, and part of it in many species is enlarged into a pouch, which is called the crop, because it occupies the same position, and performs analogous functions with that organ in birds. It is enough to say that the food remains there some time before passing on to the other parts of the intestinal canal, and undergoes a certain amount of preparation. It is in the gizzard, when one exists, that the food, separated by the masticatory organs of the mouth, undergoes another and more complete grinding. Its structure is suited to its office. It is, in fact, very muscular, often half cartilaginous, and strongly contractile. Its interior walls are provided with a grinding apparatus, which varies according to the species, and consists of teeth, plates, spines, and notches, which convert the food into pulp. It only exists among insects which live on solid matters, hard vegetables, small animals, tough skin, &c. This apparatus is absent in sucking insects and those which live on soft substances, such as the pollen of flowers, &c.

The chylific ventricle or stomach is never absent; it is the organ which performs the principal part in the act of digestion.

Two kinds of appendages belong to the chylific ventricle, but only in certain families. The first are papillæ, in the form of the fingers of a glove, which bristle over the exterior of this organ, and in which it is believed that the food begins to be converted into chyle. The second are cæca, and larger and less numerous.

They have been considered as secretory organs, answering to the pancreas in vertebrate animals.

Fig. 10, which represents the digestive apparatus of _Carabus auratus_, a common beetle, presents to the eyes of the reader the different organs of which we are speaking.

A is the mouth of the insect, B the oesophagus, C the crop, D the gizzard, E the chylific ventricle, F and G the small and large intestines, and H the anus.

It is not necessary to consider the other parts of the alimentary canal in insects, but only to refer to some of the appendages of this apparatus.

The salivary glands pour into the digestive tube a liquid, generally colourless, which, from the place where it is secreted, and its alkaline nature, corresponds to the saliva in vertebrate animals. It is this liquid which comes from the tongue of sucking insects in the form of drops.

These glands are always two in number. Their form is as variable as complicated. The most simple is that of a closed flexible tube, generally rolled into a ball, and opening on the sides of the oesophagus.

At the posterior extremity of the chylific ventricle are inserted a variable number of fine tubes, usually elongated and flexible, and terminating in _culs-de-sac_ at one end. Their colour, which depends on the liquid they may contain, is sometimes white, but more frequently brown, blackish, or green. They appear to be composed of a very slight and delicate membrane, as they are very easily torn, and nothing is more difficult than to unroll and to disengage them from the fatty or other tissues by which they are enveloped.

The function of these vessels is uncertain. Cuvier and Léon Dufour supposed them to be analogous to the liver, and on that account they have been called biliary vessels; and they are often termed the Malpighian vessels, after the name of their discoverer.

According to M. Lacordaire, their functions vary with their position. When they enter the chylific ventricle, they furnish only bile; bile and a urinary liquid when they enter the posterior part of the ventricle and the intestine; and urine alone when they are placed near the posterior extremity of the alimentary canal.