The Insect World. Figuier Louis
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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.
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.
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, α, privative, and πτερον, 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.
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.