MOSQUITO.
Blachr, . . . . HIND. Kosi, TAM, Namuk, Ages, . MALAY. Domq, TEL.
Agih Sivri-sinek, . . . TURK.
Species known are Culex laniger, C. fuscanus, C. circutuvolens, and C. regius. These insects chiefly abound near stagnant water and near the great rivers. Along the banks of the Irawadi, every Burman sleeps under -a mosquito curtain, the insects are so numerous. Their passage from a river or tank is intercepted by trees, and at Kim mendyne myriads hang about the trees. The mosquito has three stages of existence, in two of which it is a water insect, in the third the well known winged one. On a 6th May, at 6 A.m., Dr. W. Gilchrist observed several mosquitoes on the surface of some stagnant water, each in close proximity to a yellowish substance, which, when viewed through a microscope, proved to be a collection of eggs that the mosquitoes were de positing ; each collection, though consisting of not fewer than 100 eggs, did not exceed 3-20ths of an inch in length, and about 1-20th of an inch in breadth. These eggs were arranged in lines, standing on end, and were each about 1-40th of an inch long ; the lower end being larger than the upper, so that the upper surface of the col lection was somewhat concave. A few of these collections of ova were carefully introduced, with some of the water on which they floated, into a tumbler, and placed under a glass shade. Ex cepting a change of colour, from a yellow to a dark brownish-grey, which occurred within six hours after being put into the tumbler, no visible alteration took place till two days and a half, when the water was found to swarm with animal culm. The shells of the ova were still adherent, as when first observed. On examining one minutely, the larger or under end was found to have opened, like a lid, to allow the insect to escape into the water. A lady's thimble, furnished with a lid, would resemble exactly the appearance of what is being described. The design of having the lids placed at the bottom is evidently to allow the newly-hatched animalculw immediate exit from the shell into the water ; and .the con cavity of the whole collection, above alluded to, effectually tends to retain the large ends under most. Had the ova been arranged promiscuously, as to the large and small ends being upwards and downwards, it is evident that the newly-hatched insects, under the former arrangement, would have some difficulty in reaching the water, a difficulty that most probably would amount to an impossibility,—one which, at all events, is effect ually prevented by the concave form of the collection. In the newly-hatched insect, the chest or thorax (the heart is seen, obscurely however, the body being only semi-transparent) is furnished with four projections ; from this organ two blood-vessels proceed down the centre of the body, to the end of the elongation, the extreme termination of which is to be seen just above the surface of the water, where the insect lives for the most part ; the body being suspended, as it were, from this, head lowermost. Between the heart, in the thorax, and the extremity of this singular elongation, an active sanguiferous circu lation is to be observed ; in all probability, there fore, it is the seat of the lungs or gills, and it would appear that a comparatively large supply of air is essential to the existence of the insect, as it lives as much as possible in this pendulous position at the surface, with the extremity of the elongation rising just above. Its motion, which is quick, is effected by a rapid bending of its whole body, so that the head and tail (the latter consisting of a bundle of delicate filaments) ap proximate alternately on either side of the body. It always goes tail foremost, so that the head is dragged along behind. When in search of food, it throws out, in advance of its mouth, a couple of delicate brushes, the individual filaments of which are of microscopic size. Each of these is put in rapid circular motion, whereby a double kind of whirlpool is occasioned. Whatever food comes within the sphere of these vortices is speedily devoured. The food appears to be principally decomposing vegetable matter, some of which he put into the tumbler, as the vessel in which the ova were discovered contained it ; on this they fed voraciously. They did not, how ever, entirely confine themselves to a vegetable diet. He was much amused with one, when in a drop of water, under the microscope ; in these confined limits its appetite did not forsake it, and the only article of food it found was the head of one of its bwn species. So soon as this came
within the vortex, it was ravenously seized, but, being apparently too large a morceau, it was let go, after sundry futile attempts at swallowing. It frequently came within the whirlpool again, and was as often seized, but with no better success. They, however, eat the shells they had recently quitted. Some that were kept in clean water, without food, died on the third day. In this stage of their existence the insects were lively, and grew apace. At the termination of 21 days, during which the water was thrice changed, they had attained three or four twentieths of an inch in length. On attaining this size or age, they underwent a second metamorphosis. Most likely they cast their former envelope, for the hairs, so conspicuous on the former insect, were not to be seen on the present. The shape, it will be re marked, has materially altered, but the most remarkable change is that which occurs with respect to the seat of the lungs or gills. These organs are now situate in the thorax, their former seat has disappeared, and the channel of communi cation now between them and the air are two small tubes on the top of the chest. In this stage of their existence the insects are much less active than during the former one. A still greater con trast, however, is that now they do not require food, and have no mouth ; in this respect resem bling the chrysalis stage of the butterfly tribe. But the demand for air appears increased; they rarely leave the surface of the water, and when they do descend, they take down a supply of air, small globules of which are distinctly to be ob served at the end of the tube. Their descent is accomplished by striking the water with their body, but, being specifically lighter than that fluid, they rise without any effort to the surface, though in case of despatch can impel themselves upwards by the same means as they descended. However, as has been remarked, they seldom leave the surface, and, having done so, speedily return to it. The insects remain about 48 hours in this stage, towards the termination of which the legs and proboscis of the winged mosquito can be distinctly seen through the thin membrane that surrounds it. This in due course bursts, when the winged mosquito draws itself out, stands on the surface of the water a few minutes to dry and expand its wings, on which it presently pro ceeds to a dry situation. If the mosquito, when in either of the first two stages, be taken out of the water, it speedily dies, and it is as speedily deprived of life if immersed in that fluid imme diately after becoming the winged insect. We learn from the above that the mosquito is a most prolific insect, and that, as stagnant water, such as that of tanks, etc., is necessary to its propaga tion, all such ought to be kept as distant as possible. Next to the torture which Culex laniger inflicts, its most annoying peculiarities are the booming hum of its approach, its cunning, its audacity, and the perseverance with which it renews its attacks, however frequently repulsed. Various substances are employed by the Chinese to drive them away. In India they are smoked out of a room by burning chips. A few sprigs of wormwood placed about the pillow will generally protect the sleeper from their attacks ; or rub the wormwood gently over the forehead and wrists the last thing at night, and neither mosquitoes nor other noxious insects will give annoyance.
Captain Elphinstone Erskine also mentions that whenever the mosquitoes were uncommonly numer ous in Rewa (which was five miles from Niuque), he always used to be told that the boys had been disturbing the akau ni namu. This tree was completely covered with mosquitoes, and so thick were they, that one could easily have taken a capful from any branch at ono scoop. Every part of the tree, from the very top to the root, and in the same manner the branches, appeared to be one solid trunk, composed of mosquitoes. He was told by Thakonau that it had been so since he was a boy ; that it was the property of the tree to attract the mosquitoes ; and that, if never disturbed, the country would be entirely free from these troublesome insects. See Insects.