The Insect World. Figuier Louis

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СКАЧАТЬ same time the head is advanced farther towards the anterior end of the covering; but as it advances in this direction, it rises more and more, the anterior and posterior ends of the sheath thus becoming quite empty. The sheath then becomes a sort of boat, into which the water does not enter; and it would be fatal if it did. The water could not find a passage to the farther end, and the edges of the anterior end could not be submerged until the other was considerably sunk. The gnat itself is the mast of its little boat. Large boats, which pass under bridges, have masts which can be lowered; as soon as the boat has passed the bridge the mast is hoisted up by degrees, until it is perpendicular. The gnat rises thus until it becomes the mast of its own little boat, and a vertical mast also. It is difficult to imagine how it is able to put itself in such a singular, though for it necessary, position, and also how it can keep it. The fore part of the boat is much more loaded than the other, but it is also much broader. Any one who observes how deep the fore part of the boat is, and how near the edges of its sides are to the water, forgets for the time being that the gnat is an insect that he would willingly destroy at other times. One feels uneasy for its fate; and the more so if the wind happens to rise, particularly if it disturbs the surface of the water. But one sees with pleasure that there is air enough to carry the gnat along quickly; it is carried from side to side; it makes different voyages in the bucket in which it is borne. Though it is only a sort of boat—or rather mast, because its wings and legs are fixed close to its body, it is perhaps, in proportion to the size of its boat, a larger sail than one would dare to put on a real vessel—one cannot help fearing that the little boat will capsize. * * * As soon as the boat is capsized, as soon as the gnat is laid on the surface of the water, there is no chance left for it. I have sometimes seen the water covered with gnats which had perished thus as soon as they were born. It is, however, still more extraordinary that the gnat is able to finish its operations. Happily they do not last long; all dangers may be passed over in a minute.

      "The gnat, after raising itself perpendicularly, draws its two front legs from the sheath, and brings them forward. It then draws out the two next. It now no longer tries to maintain its uneasy position, but leans towards the water; gets near it, and places its feet upon it; the water is sufficiently firm and solid support for them, and is able to bear them, although burdened with the insect's body. As soon as the insect is thus on the water it is in safety; its wings are unfolded and dried, which is done sooner than it takes to tell it, at length the gnat is in a position to use them, and it is soon seen to fly away, particularly if one tries to catch it."

       Fig. 31.—Eggs of the Gnat, magnified.

      One more word about the gnat, whose life is full of such interesting details.

      The reader will perhaps not feel much pleasure in learning that the fecundity of these insects is extraordinary. Many generations are born in a single year, each generation requiring only three weeks or a month to arrive at a condition to bring forth a new generation. Thus, the number of gnats which comes into existence in the course of a year is something fearful. Only a few days after the pupæ in a bucket are transformed into gnats, eggs which have been left by the females may be observed on the surface of the water in little clusters.

      Many species of gnats, known as mosquitoes, are to be found in America. All travellers speak of the sufferings endured by a stranger in that country from the bites of these insects. One can only preserve oneself from these cruel enemies during sleep by hanging gauze, called a mosquito curtain, round the bed. Mosquito curtains are not only necessary in America; during the hot season, in Spain, throughout the whole of Italy, and a part of the south of France, it is necessary to hang these curtains round the bed, if one wishes to obtain any sleep; it is also a necessary precaution not to have a light in one's bedchamber, as the sight of it at once attracts these dangerous companions, whose buzzing and stinging prevent any possibility of repose during the whole night. Such is our advice to people who travel in the above-mentioned countries.

      The Tipulidæ have a narrow, elongated abdomen, and long and slight limbs. The head is round, and the eyes, which are compound, are, especially in the males, very large. The wings, which are long and narrow, are sometimes held wide apart, sometimes horizontally, and sometimes bent so as to form, as it were, a roof. The balancers are naked and elongated; the abdomen long, cylindrical, and often terminating in a club in the male, and in a point in the female. The antennæ, which are longer than the head, are generally composed of from fourteen to sixteen joints, and are sometimes in the form of a comb or saw, sometimes furnished with hair, in form of plumes, bunches, or in a whorl. The larvæ live on plants, in the fields, in gardens, and sometimes in woods. The perfect insects, at first sight, resemble gnats, but are without a trunk, or rather their trunk is extremely short, terminating in two large lips, and the sucker is composed of two fibres only. [12] The larger species of Tipulæ, which are commonly known as "Daddy Longlegs," &c., and in France as "Tailleurs" and "Couturières," are found in fields at the end of September and commencement of October.

      

      "Although they sometimes fly a considerable distance," says Réaumur, "when the sun is bright and hot, they generally do not go far; often, indeed, only along the ground, or rather the top of the grass. Sometimes they only use their wings to keep them above the level of the herbage, and to take them along. Their legs, particularly the hind ones, are disproportionately large. They are three times the length of the body, and are to these insects what stilts are to the peasants of marshy and inundated countries, enabling them to pass with ease over the higher blades of grass."

      One of the smaller species has been termed culiciformis, on account of its resemblance to the gnat. The smaller are more active than the larger species which we have mentioned. Not only do they fly more rapidly, but there are some kinds which are continually on the wing. In all seasons, even during the winter, at certain hours of the day, clouds of small insects are seen in the air, which are taken for gnats: they are Tipulæ. Their flight is worthy of attention; they generally only rise and fall in the same vertical line. All these flies come from larvæ, which resemble very elongated worms, having scaly heads, generally furnished with two very small conical antennæ, and certain other organs, for the purpose of obtaining food. Their bodies are jointed without limbs, but nevertheless provided with appendages which supply their place. The larvæ of the various species are of very different habits. Some are aquatic, as that of Tipula culiciformis, a small species which is very numerous in stagnant waters.

      It is necessary to say a few words about these worm-like larvæ, which are extremely common. They are of a brilliant red colour, and inhabit little oblong bent masses of earth, thickly pierced with holes. Each hole allows a worm to extend its head, and the foremost part of its body, out of the cell, which is made of light spongy matters, remains of decayed leaves, &c. These larvæ are transformed into pupæ, in the cell in which they have lived, during the larvæ state, losing by this metamorphosis the scaly coverings of the head and of all the exterior parts. They pass into the pupa state, and have the thorax provided with dainty plumes, which probably assist in the action of respiration. This pupa is very active and quick in its movements in the water. When the moment comes for its last metamorphosis, it throws off its feathery covering in much the same manner as the gnat.

      

      Fig. 32 represents Tipula oleracea in the different stages of larva, pupa, and perfect insect.

Fig. 32.—Daddy Longlegs (Tipula oleracea).

      Other species of small Tipulæ have aquatic larvæ very similar to those which we have described. Réaumur remarked that each of these worms is lodged in a thick mass, convex at the top, formed of a transparent and adhesive white jelly. The larvæ of the larger Tipulæ are not aquatic, but are of different habits, and live under the ground; all soil which is СКАЧАТЬ