The Insect World. Figuier Louis

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      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.

      The Diptera, besides their variety and the number of their species, are remarkable on account of their profusion. The myriads of flies which rise from our meadows, which fly in crowds around our plants, and around every organised substance from which life has departed, some of which even infest living animals, are Diptera.

      The profusion with which they are distributed over the face of the globe, causes them to fulfil two important duties in the economy of Nature. On the one hand, they furnish to insectivorous birds an inexhaustible supply of food; on the other, they contribute to the removal of all decaying animal and vegetable substances, and thus serve to purify the air which we breathe. Their fecundity, the rapidity with which one generation succeeds another, and their great voracity, added to the extraordinary quickness of their reproduction, are such that Linnæus tells us that three flies, with the generations which spring from them, could eat up a dead horse as quickly as a lion could.

      These Diptera, which are worthy of so much attention, and deserve so much study with regard to the part they play in the general economy of Nature, are an object of fear and repulsion when one considers their relations to us and other animals. Gnats and mosquitoes suck our blood; the gad-fly and the species of Asilus attack our cattle. The order Diptera is composed of a great number of families, which are again divided into tribes, each comprising several genera. We shall only notice the more remarkable genera of Diptera.

      M. Macquart, the learned author of "L'Histoire Naturelle des Diptères,"[11] divides this great class of insects into two principal groups. In one of these groups, the antennæ are formed of at least six joints, and the palpi of four or five: these are called Nemocera. In the other, the antennæ consists only of three joints, and the palpi of one or two: these are the Brachycera.

      The Nemocera may generally be distinguished from the other Diptera, independently of the difference in the antennæ and palpi, by the slenderness of the body, the smallness of the head, the shape of the thorax, and the length of the feet and wings. The result of this organisation is a graceful, light, and aerial form.

      Nemocera.

      Abounding everywhere, the Nemocera live, some on the blood of man and animals, some on small insects, and others on the juices of fragrant flowers. From νημα, thread; κερας, horn.

      In all climates, in every latitude, in the fields and woods, even in our dwellings, they may be seen fluttering and plundering. The Nemocera are divided into two families, that of the Culicidæ, of which the gnat (Culex), which has a long, thin trunk, and a sucker provided with six bristles, is a member; and that of the Tipulidæ, which have a short thick trunk, and a sucker having two bristles.

      

Figs. 19 and 20.—The Gnat (Culex pipiens).

      We will begin our examination with the Gnat (Culex pipiens), of which Réaumur, in his "Mémoires pour servir à l'Histoire des Insectes," has given such a curious and complete history. "The gnat is our declared enemy," says Réaumur, in the introduction to his memoir, "and a very troublesome enemy it is. However, it is well to make its acquaintance, for if we pay a little attention we shall be forced to admire it, and even to admire the instrument with which it wounds us. Besides which, throughout the whole course of its life it offers most interesting matter of investigation to those who are curious to know the wonders of Nature. During a period in its life the observer, forgetting that it will at some time annoy him, feels the greatest interest in its life-history."

      As this is the case, let us explain the history of these insects, which excite so much interest. The illustrious naturalist we have just mentioned will be our guide.

      The body of the gnat is long and cylindrical. When in a state of repose one of its wings is crossed over the other. They present a charming appearance when seen through a microscope, their nervures, as well as their edges, being completely covered with scales, shaped like oblong plates and finely striated longitudinally. These scales are also found on all the segments of the body.

Fig. 21.—Antennæ of Gnat, magnified.		Fig. 22.—Head of Gnat, magnified.

      The antennæ of the gnat, particularly those of the male, have a fine feathery appearance (Fig. 21).

      Their eyes, covered with network, are so large that they cover nearly the whole of the head. Some have eyes of a brilliant green colour, but looked at in certain lights they appear red. Fig. 22 shows the head of the gnat with its two eyes, its antennæ, and trunk.

      The instrument which the gnat employs for puncturing the skin, and which is called the trunk (Fig. 23), is well worthy of our attention. That which is generally seen is only the case of those instruments which are intended to pierce our skin and suck our blood, and in which they are held, as lancets and other instruments are held in a surgeon's case. The case (Fig. 24) is cylindrical, covered with scales, and terminates in a small knob. Split from end to end that it may open, it contains a perfect bundle of stings. Réaumur tried to observe, by allowing himself to be stung by gnats, what took place during the attack. He forgot, in watching the operations of the insect, the slight pain caused by the wound, soliciting it as a favour, his only regret being not to obtain it when he wished.

      Réaumur observed that the compound sting, which is about a line in length, enters the skin to the depth of about three-quarters of a line, and that during that time the case bends into a bow, until the two ends meet. He noticed besides, that the trunk-case of certain gnats was even more complicated than that which we have described. But we will not dwell any longer on this point.

      Let us now try to give an idea of the construction and composition of this sting, which, after piercing the skin, draws our blood.

Figs. 23 and 24.—Trunk of Gnat, magnified.	СКАЧАТЬ В начало < 5 6 7 8 9 10 11 12 13 14 > В конец