The Insect World. Figuier Louis
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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.
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| 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.
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| Figs. 23 and 24.—Trunk of Gnat, magnified. | Figs. 25, 26, 27.—Lancets of the Gnat. |
According to Réaumur, the sting of the gnat is composed of five parts. He acknowledges, however, that it is very difficult to be certain of the exact number of these parts, on account of the way in which they are united, and of their form. At the present day we know that there are six. Réaumur, as also Leuwenhoek, thought he saw two in the form of a sword blade with three edges. These have the points reversed, and are serrated on the convex side of the bend (Fig. 25). To form an idea of the shape of the other points, the reader should look at Figs. 26 and 27. He will then see that the gnat's sting is a sword in miniature.
The prick made by so fine a point as that of the sting of the gnat ought not to cause any pain. "The point of the finest needle," says Réaumur, "compared to the sting of the gnat, is the same as the point of a sword compared to that of the needle." How is it then that so small a wound does not heal at once? How is it that small bumps arise on the part that is stung? The fact is, that it is not only a wound, but it has been imbued with an irritating liquid.
This liquid may be seen to exude, under different circumstances, from the trunk of the gnat, like a drop of very clear water.
Réaumur sometimes saw this liquid even in the trunk itself. "There is nothing better," he observes, "to prevent the bad effects of gnat bites than at once to dilute the liquid they have left in the wound with water. However small this wound may be, it will not be difficult for water to be introduced. By rubbing, it will be at once enlarged, and there is nothing to do but to wash it. I have sometimes found this remedy answer very well."
The gnat is not always in the form of a winged insect, greedy for our blood. There is a period during which they leave us in repose. This is the larva period. It is in water, and in stagnant water in particular, that the larva of the insect which occupies our attention is to be found. It resembles a worm, and may be found in ponds from the month of May until the commencement of winter.
If we desire to follow the larva of the gnat from the beginning, we have only to keep a bucket of water in the open air. After a few days this water will be observed to be full of the larvæ of the gnat (Fig. 28). They are very small, and come to the surface of the water to breathe; for which purpose they extend the opening of a pipe, A, which is attached to the last segment of the body, a little above the surface. They are, consequently, obliged to hold their heads down. By the side of the breathing-tube is another tube, B, shorter and thicker than the former, nearly perpendicular to the body, its orifice being the exterior termination of the digestive tube. At the anus it is fringed with long hairs, having the appearance, when in the water, of a funnel. At the end of the same tube, and inside the hair funnel, are four thin, oval, transparent, scaly blades, having the appearance of fins. They are placed in pairs, of which one emanates from the right side, the other from the left.
These four blades or fins have the power of separating from each other. Each segment of the abdomen has on both sides a tuft of hair, and the thorax has three. The head is round and flat, and is provided with two simple brown eyes. Round the mouth are several wattles, furnished with hair, of which two of crescent-like form are the most conspicuous. These tufts move with great quickness, causing small currents of liquid to flow into the mouth, by means of which the necessary food, microscopic insects and particles of vegetable and earthy matter, is brought to the larva.
They change their skin several times during their continuance in this state. This latter fact has been remarked by Dom Allou, a learned Carthusian, "whose pleasure," says Réaumur, "consisted in admiring the works of the Almighty, when not occupied in singing his praises." We think it will be interesting to repeat the few lines which accompany the mention made by Réaumur of this worthy Carthusian. They appear to us to be well worth reading, even at the present day.
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