The Insect World. Figuier Louis

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СКАЧАТЬ they are to be found especially in low damp meadows.

      Réaumur saw large districts of grassy swamps in Poictou, which, in certain years, furnished very little grass for the cattle, on account of the ravages caused by these larvæ. They had also much injured the harvest in the same districts during those years.

      These larvæ appear to require no other food than vegetable mould. Their excrements are, in fact, according to Réaumur, nothing else than dried earth, from which the stomach and intestines of the insect have withdrawn all nourishing matter.

      Old trees have often hollow cavities occasioned by the decay of the trunk. When these cavities are old, their lower parts are full of a sort of mould, which is in fact half-decayed wood. It is there that the Tipulæ often lay their eggs. Réaumur frequently found the larvæ in the trunks of elms or willows, and also in the fleshy parts of certain kinds of mushrooms. He carefully observed the habits of one, which lived under the covering of a mushroom, the Oak agaric (Agaricus quercinus). This larva is round, grey, and resembles an earth-worm. It does not walk, but crawls; and the places where it stops, or which it passes over, are covered with a sort of brilliant slime, like that left by the snail or slug.

      M. Guérin-Méneville has published some very interesting remarks on the migrations of the larvæ of a particular kind of Tipula, known by the name of Sciara. We will borrow from that entomologist the following curious details, which will initiate us into one of the most wonderful phenomena in the whole history of insects. These small larvæ are without feet, hardly five lines in length, and about the third of a line in diameter. They are composed of thirteen segments, and have small black heads.

      In some years, during the month of July, may be found on the borders of forests in Norway and Hanover, immense trains of these larvæ, formed by the union of an innumerable quantity fixed to each other by a sticky substance. These collections of larvæ resemble some sort of strange animal of serpent-like form, several feet long, one or two inches in thickness, and formed by the union of an immense number, which cling to each other by thousands, and move on together. The whole society advances thus with one accord, leaving a track after it on the ground, as a material indication of its presence.

      These strange collections of living creatures form societies, sometimes only a few yards long; but at other times it happens that they form bands from ten to twelve yards in length, of the breadth of a hand and the thickness of a thumb. M. Guérin-Méneville observed columns as many as thirty yards in length. These troops advance as slowly as a snail, and in a certain direction. If they encounter an obstacle—as a stone, for instance—they cross over it, turn round it, or else divide into two sections, which reunite after the obstacle is passed. If a portion of the column be removed so as to divide it into two parts, it is quickly reunited, as the hindmost portion soon joins that which precedes it. Lastly, if the posterior part of this living ribbon be brought into contact with the anterior, a circle is formed, which turns round and round on the same ground for a long time, sometimes even for a whole day, before breaking, and continuing to advance. They are never met with in bad weather, but only when the sun is warm.

      The curious and astonishing phenomenon of an assembly of larvæ without feet, advancing with an equal movement resulting from the individual motion of thousands of little worms, was remarked for the first time, in 1603, by Gaspard Schwenefelt. This naturalist says that the inhabitants of Siberia consider this phenomenon as an indication of a bad harvest if they go towards the mountains; whereas, if they descend towards the plains, it is the sign of a good one. In 1715 Jonas Ramus mentioned the same phenomenon, recalling a superstition attached to it by the peasants of Norway. This writer informs us that the peasants of that country, on meeting one of these moving columns, throw down their belts or waistcoats on the ground before it. If the orme-drag (that is the name given to the moving column) crosses over this obstacle, it is a good sign; but on the other hand, if the column turns round the obstacle, instead of crossing it, some mischief may be expected.

      The same animals were observed in 1845 at Birkenmore, near Hefeld, by M. Rande, Royal Inspector of the Forests of Hanover.

      M. Guérin-Méneville is of opinion that these larvæ, which exist in great numbers in certain districts, sometimes devour all the nutritive substances contained in the ground. After having done so, they are obliged to come out of it, in order to seek at a distance a place where they will find food, or perhaps only a suitable place to undergo their metamorphosis. It is then that this singular journey commences. As regards the uniting of these myriads of individuals into columns, M. Guérin-Méneville thinks that it can be explained by the necessity these insects feel for mutual protection against the drying effect of the atmosphere when they are forced to leave the ground. United into masses, and moistened by the glutinous matter which connects them, they can leave their former place of abode without danger; if each were by itself, they would soon perish. Here, as in other cases, union is strength; and the strength of these larvæ lies in this protecting moisture. However it may be explained, the migration of these troops of insects are among the most astonishing phenomena of Nature.

      Brachycera.

      The Brachycera, from βραχυς, "short;" and κερας, "a horn" —these Diptera having short antennæ—are divided into four groups. In this subdivision the sucker is composed of six bristles. Amongst other families it includes that of the Tabanidæ; the insects belonging to which family are of remarkable strength, and possessed of daring and courage in the highest degree. Their wings are provided with powerful muscles, their feet are very strong, and their trunk is provided with six flat, sharp lancets. Distributed over the entire world, their instinct is everywhere the same, it is the desire for blood, at least in the females; for the males are not so warlike, they do no harm, but live on the juices of flowers. They are chiefly found in woods and pastures, and during the hottest part of the day in summer may be seen flying about seeking for their prey.

      M. de Saint-Fargeau has described the manner in which the males fly. They may be seen flying hither and thither in the glades of woods, remaining for some time suspended in the air, then darting quickly and suddenly away a yard or two, again taking up the same immovable position, and in each of these movements turning the head to the opposite way from that in which they are going. This naturalist is certain that on these occasions they are watching for the females, which they dart upon. When they have succeeded in doing so, they rise so high as to be out of sight.

      To this group belongs the genus Tabanus.

      The first species we shall mention, Tabanus autumnalis (Fig. 33), a common species, is eight or nine lines in length, and of blackish colour. The palpi, the face, and the forehead are grey; the antennæ black; the thorax grey, striped with brown; the abdomen spotted with yellow; the legs of a yellowish white; and the outer edge of the wings brown.

      Another species (Tabanus bovinus) is twelve lines in length, and of a blackish brown. The palpi, the face, and the forehead are yellow; the antennæ black, with a whitish base; the thorax, covered with yellow hair, is striped with black; the posterior edge of the segments of the abdomen pale yellow; the legs yellowish, with the extremities black, and the exterior edge of the wings yellow. This species is frequently met with in woods.

      A third species, Chrysops cæcutiens (Fig. 34), which belongs to the same family, and of which the generic name Chrysops signifies golden-eyed, torments horses and cattle very much by biting them round the eyes. Its thorax is of a yellowish colour, striped or spotted with black; the abdomen yellow, and the eyes golden.

      In the next group of the Brachycera the sucker is composed of four bristles, and the antennæ generally terminate in a point which appears to be rather a development than an appendage.

      This group includes СКАЧАТЬ