Part 3

M. Plateau has studied the power of traction in some insects, the power of pushing in the digging insects, and the lifting power of others during flight. He has thus been able to make some most interesting comparisons, of some of which we will relate the results.

The average weight of man being 142 lbs., and his power of traction, according to Régnier, being 124 lbs., the proportion of the weight he can draw to the weight of his body is only as 87 to 100. With the horse the proportion is not more than 67 to 100, a horse 1,350 lbs. in weight only drawing about 900 lbs. The horse, therefore, can draw little more than half his own weight, and a man cannot draw the weight of his own body.

This is a very poor result, if compared with the strength of the cockchafer. This insect, in fact, possesses a power of traction equal to more than fourteen times its own weight. If you amuse yourself with the children's game of making a cockchafer draw small cargoes of stones, you will be surprised at the great weight which this insignificant looking animal is able to manage.

To test the power of traction in insects, M. Plateau attached them to a weight by means of a thread fastened to one of their feet. The _Coleoptera_ (Beetles) are the best adapted for these experiments.

The following are some of the results obtained by the Belgian physician:--_Carabus auratus_ can draw seven times the weight of its body; _Nebria brevicollis_, twenty-five times; _Necrophorus vespillo_, fifteen times; _Trichius fasciatus_, forty-one times; and _Oryctes nasicornis_, four times only. The bee can draw twenty times the weight of its body; _Donacia nymphæ_[7] forty-two times its own weight.

[7] A beetle.--ED.

From this it follows that if the horse possessed the same strength as this last insect, or if the insect were the size of a horse, they would either of them be able to draw 155,250 lbs. M. Plateau has ascertained the pushing power in insects, by introducing them into a pasteboard tube, the interior of which was made rough, and in which was fixed a glass plate, which allowed the light to penetrate into the prison. The animal, if excited, struggled with all its strength against the transparent plate, which, on being pushed forward, turned a lever adapted to a miniature dynamometer, which indicated the amount of effort exercised.

The results thus obtained prove that the pushing power, like the power of traction, is greater in inverse proportion to the size and weight of the animal. A few figures will better explain this curious law. In _Oryctes nasicornis_ the proportion of the pushing power to the weight of the insect is only three to two; in _Geotrupes stercorarius_ it is sixteen to two; and in _Onthophagus nuchicornis_ seventy-nine to six.

Experiments have been made on the lifting power of insects by fastening a ball of soft wax to a thread attached to the hind legs. The proportion of the weight lifted has been found equal to that of the body. That is to say, that the insect, when flying, can lift its own weight. This is proved by the following calculations:--In the Neuroptera the proportion is 1 in the Dragon-fly (_Libellula vulgata_), ·7 in _Lestes sponsa_. In the order Hymenoptera it is ·78 in the bee, and ·63 in _Bombus terrestris_, the humble-bee. In the Diptera it is ·9 in _Calliphora vomitoria_,[8] 1·84 in the _Syrphus corollæ_, and 1·77 in the house-fly.

[8] The meat-fly.--ED.

These results show that insects have only sufficient power to sustain their own weight when flying, as the above calculations exhibit the maximum of which they are capable, and at the utmost this strength would only compensate for the fatigue occasioned by the action of flight.

At the same time it is to be observed that the Diptera, and among others the house-fly, can sustain their flight longer than the Hymenoptera and Neuroptera, although one would not think so from their appearance. In conclusion, if an insect's power of flying is not considerable, its power of traction and propulsion are immense, compared with the vertebrate animals; and, in the same group of insects, those that are the smallest and lightest are the strongest. The proportion between the muscular strength of insects and the dimensions of their bodies, would not appear to be on account of their muscles being more numerous than those of vertebrate animals, but on account of greater intrinsic energy and muscular activity. The articulations of insects may be considered as solid cases which envelop the muscles, and the thickness of these cases appears to decrease in a singular manner according to the size of the creature. The relative bulk of the muscles being less in the smaller species than in the larger, it is necessary to explain the superior relative strength of the former by supposing them to possess a greater amount of vital energy.

These astonishing phenomena will perhaps be better understood if we consider the obstacles which insects have to overcome to satisfy their wants, to seek their food, to defend themselves against their enemies, &c.

To meet these requirements they are marvellously constructed for both labour and warfare, and their strength is superior to that displayed by all other animals. It is also much greater than that of the machines we construct to replace manual labour. They represent strength itself. God's workmen are infinitely more powerful than those invented by the genius of man, which we call machines.

We think it necessary, in closing this chapter, to give a sort of general outline of the great class of animals which we are about to study. If we wished to characterise insects by their exterior aspect, we might consider them as articulate animals, whose bodies, covered with tough and membranous integuments, are divided into three distinct parts: the head, provided with two antennæ, and eyes and mouth of very variable form; a trunk or thorax, composed of three segments, which has underneath it always six articulated limbs, and often above it two or four wings; and an abdomen, composed of nine segments, although some may not appear to exist at first sight.

If, in addition to these characteristics, one considers that these animals are not provided with interior skeletons--that their nervous system is formed of a double cord, swelling at intervals, and placed along the under-side of the body, with the exception of the first swellings or ganglions which are under the head--that they are not provided with a complete circulating system--that they breathe by particular organs, termed tracheæ, extending parallel to each other along each side of the body, and communicating with the exterior air by lateral openings termed spiracles--that their sexes are distinct--that they are reproduced from eggs--and, in conclusion, that the different parts we have mentioned are not complete until the creature has passed through several successive changes, called metamorphoses, a general idea may be formed of what is meant in zoology by the word "insect."

Insects, whose general organisation we have briefly traced, have been classed by naturalists as follows:--

1. APTERA (Fleas and Lice). 2. DIPTERA (Gnats, Flies, &c.) 3. HEMIPTERA (Bugs, &c.) 4. LEPIDOPTERA (Butterflies and Moths). 5. ORTHOPTERA (Grasshoppers, Crickets, Cockroaches, &c.) 6. HYMENOPTERA (Bees, Wasps, &c.) 7. THYSANOPTERA (_Thrips cerealium_). 8. NEUROPTERA (_Libellula_, or Dragon-fly; _Ephemera_, or May-fly; _Phryganea_, or Alder-fly). 9. COLEOPTERA (Beetles).

We shall commence the history of the various orders by examining the Aptera.

I.

APTERA.

Insects of this order are without wings, and the name is derived from two Greek words, [Greek: a], privative, and [Greek: pteron], wing, indicating the negative character which constitutes this order.[9] It consists of Fleas and Lice. The Flea (_Pulex_), of which De Geer formed a separate group, and called _Suctoria_, includes several species.

[9] It is probable that one day the order Aptera will be superseded. The absence of wings is not really a character of great value. De Blainville, Mollard, Pouchet, Van Beneden, and Gervais, have made several attempts in that direction. The fleas have been placed among the Diptera, and the lice among Hemiptera in the "Traité de Zoologie Médicale" of these two last authors.

The common flea (_Pulex irritans_, Fig. 17) has a body of oval form, somewhat flattened, covered with a rather hard horny skin of a brilliant chestnut brown colour. It is the breaking of this hard skin which produces the little crack which is heard when, after a successful hunt, one has the happiness to crush one of these parasites between one's nails.

Its head, small in proportion to the body, is compressed, and carries two small antennæ, of cylindrical form, composed of four joints, which the animal shakes continually when in motion, but which it lowers and rests in front of its head when in a state of repose. The eyes are simple, large, and round. The beak is composed of an exterior jointed sheath, having inside it a tube, and carrying underneath two long sharp lancets, with cutting and saw-like edges. It is with this instrument that the flea pierces the skin, irritates it, and causes the blood on which it lives to flow.

This bite, as every one knows, is easily recognised by the presence of small darkish red spots, surrounded by a circle of a paler colour. The quantity of blood absorbed by this little creature is enormous, when compared with its size.

The body of the flea is divided into thirteen segments, of which one forms the head; three the thorax, which is short, and the remainder the abdomen.

The limbs are long, strong, and spiny. The tarsus, or foot, has five joints, and terminates in hooks turned in opposite directions. The two anterior limbs are separated from the others, and are inserted nearly under the head; the posterior ones are particularly large and strong.

The jumps which fleas are able to make are really gigantic, and the strength of these little animals quite herculean, when compared with the size of their bodies. The reader may be inclined to smile at the assertion that the flea possesses herculean strength; but let him wait a little, and he will find that it is no exaggeration.

To give some idea of the strength, the docility, and the goodwill of the fleas, some wonderful little things have been made, which have served at the same time to show the astonishing skill of certain workmen.

In his "Histoire abrégée des Insectes," published in the seventh year of the French Republic, Geoffroy relates that a certain Mark, an Englishman, had succeeded, by dint of patience and art, in making a gold chain the length of a finger, with a padlock and a key to fasten it, not exceeding a single grain in weight. A flea attached to the chain pulled it easily. The same learned writer relates a still more surprising fact. An English workman constructed a carriage and six horses of ivory. The coachman was on the box, with a dog between his legs, there were also a postillion, four persons in the carriage, and two servants behind, and the whole of this was drawn by one flea.

In his "Histoire Naturelle des Insectes Aptères," Baron Walckenaer relates the following marvellous instance of industry, patience, and dexterity:--

"I think it is about fifteen years ago, that the whole population of Paris could see the following wonders exhibited on the Place de la Bourse for sixty centimes. They were the learned fleas. I have seen and examined them with entomological eyes, assisted by a glass.

"Thirty fleas went through military exercise, and stood upon their hind legs, armed with pikes, formed of very small splinters of wood.

"Two fleas were harnessed to and drew a golden carriage with four wheels and a postillion. A third flea was seated on the coach-box, and held a splinter of wood for a whip. Two other fleas drew a cannon on its carriage; this little trinket was admirably finished, not a screw or a nut was wanting. These and other wonders were performed on polished glass. The flea-horses were fastened by a gold chain attached to the thighs of their hind legs, which I was told was never taken off. They had lived thus for two years and a half, not one having died during the period. To be fed, they were placed on a man's arm, which they sucked. When they were unwilling to draw the cannon or the carriage, the man took a burning coal, and on it being moved about near them, they were at once roused, and recommenced the performances."

The learned fleas were the admiration and amazement of Paris, Lyons, and the chief provincial towns of France, in 1825.

But how, one will ask, was it possible in a large public room to see this wonderful sight? And it is necessary that this should be explained. The spectators were seated in front of a curtain, provided with magnifying glasses, through which they looked, as they would at a diorama of landscapes or buildings.

But let us return to the natural history of our insect. The female flea lays from eight to twelve eggs, which are of oval shape, smooth, viscous, and white.

Contrary to what one might think, _à priori_, the flea does not fix its eggs to the skin of its victims. She lets them drop on the ground, between the boards of floors, or old furniture, and among dirty linen and rubbish.

M. Defrance has remarked that there are always found mixed with the eggs a certain number of grains of a brilliant black colour, which are simply dried blood. This is a provision which the foreseeing mother has prepared at our expense to nourish her young offspring.

In four or five days in summer, and in eleven days in winter, one may see coming out of these eggs small, elongated larvæ, of cylindrical form, covered with hair, and divided into three parts, the last provided with two small hooks. The head is scaly above, has two small antennæ, and is without eyes. These larvæ are without limbs, but they can twist about, roll themselves over and over, and even advance pretty fast by raising their heads. Though at first white, they become afterwards of a reddish colour.

About a fortnight after they are hatched they cease to eat, and are immovable, as if about to die. They then commence to make a small, whitish, silky cocoon, in which they are transformed into pupæ. In another fortnight these pupæ become perfect insects.

A most remarkable trait, and unique among insects, has been observed in the flea. The mother disgorges into the mouths of the larvæ the blood with which she is filled.

The flea is most abundant in Europe and the North of Africa. Certain circumstances particularly favour its multiplication; being most abundant in dirty houses, in barracks, and in camps; in deserted buildings, in ruins, and in places frequented by people of uncleanly habits.

Other kinds of fleas live on animals, as, for example, the cat flea, the dog flea, and those of the pigeon and poultry.

We shall say a few words about a peculiar species which abounds in all the hot parts of America, but principally in the Brazils and the neighbouring countries. This formidable species is the Chigo (_Pulex penetrans_).

The chigo, called also the tick, is smaller than the common flea. It is flat, brown with a white spot on the back, and is armed with a strong pointed stiff beak, provided with three lancets. It is with this instrument that the female attacks man with the intention of lodging in his skin and bringing forth her young there.

The chigo attacks chiefly the feet. It slips in between the flesh and the nails, or gets under the skin of the heel. Notwithstanding the length of the animal's beak, introducing itself beneath the skin does not at first cause any pain; but after a few days one is made aware of its presence by an itching, which, though at first slight, gradually increases, and ends by becoming unbearable.

The chigo, when under the skin, betrays itself by a bump outside. Its body has now become as large as a pea; in the attacked skin a large brown bag containing matter is formed. In this bag are collected the eggs, which issue from an orifice in the posterior extremity, and are not hatched in the wound itself, as was long thought to be the case.

The chigoes are an object of terror to the Brazilian negroes. These formidable parasites sometimes attack the whole of the foot, which they devour, and thus bring on mortification; many negroes losing the bones of some of their toes by the ravages of these dangerous creatures. To guard against their attacks, they wear thick shoes, and examine their feet carefully every day. The plan usually followed in the Brazils to prevent the chigoes from injuring the feet, is to employ children, who, by their sharpness of sight, can easily perceive the red spot on the skin where the chigo has entered. These children are in the habit of extracting the insect from the wound by means of a needle. But this is not without risk; as, if any portion of the insect remains in the wound, a dangerous inflammation may ensue. For this reason, operators who are renowned for their skill are much sought after, flattered, and rewarded by the poor negroes of the plantations.

The Head Louse (_Pediculus capitis_, Fig. 18) is an insect with a flat body, slightly transparent, and of greyish colour, spotted with black on the spiracles, soft in the middle, and rather hard at the sides. The head, which is oval, is furnished with two thread-like antennæ, composed of five joints, which are constantly in motion while the creature is walking; it is also furnished with two simple, round, black eyes; and lastly, with a mouth. In the front of the head is a short, conical, fleshy nipple. This nipple contains a sucker, or rostrum, which the animal can put out when it likes, and which, when extended, represents a tubular body, terminating in six little pointed hooks, bent back, and serving to retain the instrument in the skin. This organ is surmounted by four fine hairs, fixed to one another, and seated in its interior. It is by means of this complicated apparatus that the louse pricks and sucks the skin of the head. The thorax is nearly square, and divided into three parts by deep incisions. The abdomen, strongly lobed at the sides, is composed of eight rings, and is provided with sixteen spiracles. The limbs consist of a trochanter, a thigh, a shank, and a tarsus of a single joint, and are very thick. A strong nail, which folds back on an indented projection, thus forming a pincer, terminates the tarsus. It is with this pincer that the louse fastens itself to the hair.

Lice are oviparous. Their eggs, which remain sticking to the hair, are long and white, and are commonly called "nits." The young are hatched in the course of five or six days; and in eighteen days are able to reproduce their kind. Leuwenhoek calculated that in two months two female lice could produce ten thousand! Other naturalists have asserted that the second generation of a single individual can amount to two thousand five hundred, and the third, to a hundred and twenty-five thousand! Happily for the victims of these disgusting parasites, their reproduction is not generally to this prodigious extent.

Many means are employed to kill lice. Lotions of the smaller centaury or of stavesacre, and pomatum mixed with mercurial ointment, are very efficacious. But the surest and easiest remedy is to put plenty of oil on the head. The oil kills the lice by obstructing their tracheæ, and thus stopping respiration.

There are other kinds of lice, but we will only mention the louse which infests beggars and people of unclean habits, _Pediculus humanus corporis_, producing the complaint called phthiriasis. In the victims of this disease these parasites increase with fearful rapidity. This dreadful disorder is often mentioned by the ancients. King Antiochus, the philosopher Pherecydes of Scyros, the contemporary and friend of Thales, the dictator Sylla, Agrippa, and Valerius Maximus, are said to have been attacked by phthiriasis, and even to have died of it. Amatus Lusitanus, a Portuguese doctor of the sixteenth century, relates that lice increased so quickly and to such an extent on a rich nobleman attacked with phthiriasis, that the whole duty of two of his servants consisted in carrying away, and throwing into the sea, whole basketfuls of the vermin, which were continually escaping from the person of their noble master.

Little is known at the present day of the details of this complaint, though it is observed frequently enough in some parts of the south of Europe, where the dirty and miserable inhabitants are a prey to poverty and uncleanliness--two misfortunes which often go together. In Gallicia, in Poland, in the Asturias, and in Spain, we may find many victims of phthiriasis.

Lice increase with such rapidity on persons thus attacked, that it is common to attribute their appearance to spontaneous generation alone. But the prodigious rapidity of reproduction in these insects sufficiently explains their increase, especially when it is admitted that it is possible for the female louse to reproduce young without the agency of the male.

The Thysanura or "Skip Tail" tribe are small insects, which are better known on account of the beauty of their microscopic body scales than for any interesting habits or instincts. They do not undergo metamorphosis.

The Fish Scale or _Lepisma saccharina_, and the Skip Tail or _Podura plumbea_ belong to the Thysanura.

II.

DIPTERA.

All suctorial insects which in the perfect state possess only two membranous wings, are called Diptera, from two Greek words--[Greek: dis], twice, and [Greek: pteron], wing.

The Diptera were known and scientifically described at a very early date. They are frequently mentioned by Aristotle in his "History of Animals;" and he applied the term to the same insects as now constitute the order.

The absence of the second wings, common to other insects, which are in this case replaced by two appendages, which have received the name of balancers,[10] because they serve to regulate the action of flight, constitutes the chief characteristic of the Diptera. Let us, however, give a glance at their other organs, which have more or less affinity with those which exist in other classes of insects, preserving, nevertheless, their own especial characteristics.

[10] Sometimes called _halteres_.--ED.

The mouth, for instance--suited for suction only--is in the form of a trunk, and is composed of a sheath, a sucker, and two palpi. The antennæ are generally composed of only three joints. The eyes--usually two in number--are very large, and sometimes take up nearly the whole of the head. They are both simple and compound. The wings are membranous, delicate, and veined; the limbs long and slight. In giving the history of the principal types of Diptera, we shall explain more fully the formation of these organs.

The Diptera, by their rapid flight, enliven both the earth and the air. The different species abound in every climate, and in every situation, some inhabiting woods, plains, fields, or banks of rivers; others preferring our houses. They like the neighbourhood of vegetation, choosing either the flowers, the leaves, or the stems of the trees of our woods, our gardens, or our plantations. Their food varies very much; and the formation of the sucker is regulated by it. Some imbibe blood, others live on the secretions of animals. Their chief nourishment, however, consists of the juices of flowers, on whose brilliant corollas the Diptera abound, either plundering from every species indiscriminately, or attaching themselves to some particular kind. They display the most wonderful instinct in their maternal care, and employ the most varied and ingenious precautions to preserve their progeny.