Here might we point to him that wondrous and exquisite structure, the life-boat of eggs, floating[A] securely on its silent surface, or anchored, perhaps, to the side of some pond-plant's slimy stem; and lingering here we might in a few days see the little eggs become burst and give exit to a number of minute creatures of great activity. Some of them would be seen twisting themselves about in a most extraordinary manner, and swimming here and there through the still waters. Or we might take him to the depths of the forest, and now, under the bark of some of the trees, now upon their branches, now in little tents of leaves, we could point out many a colony of eggs only waiting for the life-giving influence of spring to burst into life and activity.
But it is better for us to proceed more systematically, and to notice shortly the interesting facts which the science of entomology reveals to us as to the egg-cradles, so to speak, of insects, by which is meant the various localities selected by them for the deposition of their eggs, some of them, as we have mentioned, in the water, some in the earth, some upon plants and trees, and some in mansions made by the insects themselves for the purpose of hatching their eggs.
Let us come, then, and watch the great water-beetle, at the time when the mother-insect is about to commit her future offspring to the care of the waters. She is to be found on fine days, when the sun is going down into a bed of gold, enjoying herself and delighting in the pleasant air of the evening, as she sits upon a plant close by the water's edge; or she may even have taken up her position on a floating leaf of the plant, the clear waters flowing gently beneath her. She has been in the water all day long, and is now just emerged. On other evenings she will take wing, and speed her way whither no eye can follow; but now, she has another and the most important duty of her existence to perform, and her customary evening ramble is not permitted to interfere with its fulfilment. On watching her closely we find her busy at some self-imposed occupation; what is its nature? To discover that, she must be closely and patiently watched. At her tail are a couple of spinning organs, which move from right to left and up and down with great swiftness, all the while a glutinous fluid, which hardens into a thread, being discharged from each of them. With this apparatus the industrious insect is spinning a pouch not unlike the purses which were in fashion before the long ones that ladies knit came to be adopted. This purse is three quarters of an inch long; it consists outside of a tissue, like parchment, which is quite impervious to water, but is lined inside with the most beautiful, light, downy material possible, which is as white as snow. There is a sort of little horn to this pouch, which admits the air, but the opening to which is protected by a layer of cross threads, which excludes the wet. In three hours of patient toil this beautiful cradle is completed. The water-beetle then safely secures it from being carried away by the waters on which it floats so buoyantly, by fastening it by cables to the neighbouring plants. Here safely moored it rests until the eggs are hatched, soon after which the little creatures within escape into the waters out of the ark, which has, during the period of their infancy, safely preserved them from every danger, both of water and wind.
The proceedings of the common gnat, our summer tormentor, are no less interesting and instructive. Her actions have been closely watched by the great Réaumur, and are detailed by him with very striking accuracy. They require, perhaps, sharper scrutiny than most of our readers are in the habit of bestowing upon the actions of insects, but they well repay a patient and attentive observation, and subjects for the examination may easily be found at the side of any pool in summer. The following is an outline of the difficulties the insect has to contend with in depositing her eggs. First, they must be hatched on the water; but, 2d, her eggs are heavier than water, and will therefore sink if dropped into it one by one; and, 3d, the eggs are so small and of so peculiar a shape that it would be difficult to make them stand upright on a solid surface; far more so then, on the water. A human ship-builder would be probably sorely puzzled to find out how to overcome these difficulties, and of such materials how to construct a floating raft; nay, a raft which cannot by any means be made to sink. The insect has, however, been instructed by a Greater and Wiser than man, and she solves the problem in a manner well calculated to excite our admiration and praise. Fixing herself by her four front legs upon a leaf or twig floating on the surface of the water, she stretches out behind her the two hind legs, and crosses them over one another somewhat in this manner
. In the triangular space thus formed she purposes to construct her boat of eggs. Now, all things being ready, just where the crossed legs meet she places her first egg, which is covered over with a thick glue. By the side of this she places another, and again another, so that the three are, by means of the glue which covers them, united together, and will, consequently, preserve the upright position, as there is now a sufficiently broad base of support for them to rest upon. To these she diligently adds egg to egg until she has sufficiently formed the shape of her boat; after which she uncrosses her legs and places them quite straight, so as to shape the sides of the boat. When a sufficient number of eggs have been thus glued together, the number varying from two to three hundred, the gnat considers her task as ended, and wings her way from the pool, abandoning her ingenious structure to the mercy of wind and wave, although not without the security of knowing that neither wind nor wave could commit serious injury upon it.
"In shape," write Messrs. Kirby and Spence, "this little boat pretty accurately resembles a London wherry, being sharper and higher, to use a nautical phrase, fore and aft; convex below and concave above; floating, moreover, constantly on the keel or convex part. But this," they add, "is not all; it is, besides, a life-boat, more buoyant than even Mr. Greathead's. The most violent agitation of the water cannot sink it; and what is more extraordinary, and a property still a desideratum in our life-boats, though hollow it never becomes filled with water, even though exposed to the torrents that often accompany a thunder-storm. To put this to the test I yesterday placed half a dozen of these boats upon the surface of a tumbler half full of water. I then poured upon them a stream of that element from the mouth of a great bottle held a foot above them, yet, after this treatment, which was so rough as actually to project one out of the glass, I found them floating as before upon their bottoms, and not a drop of water within their cavity."
Rubbish Towers of the Sand-Wasp.
Some insects make the homes of their young in the earth. Of these, the insect called the sand-wasp forms, perhaps, one of the most interesting examples. This insect selects generally a hard sunny sand-bank for the excavation it is about to accomplish. Armed with a pair of powerful jaws, by means of which the insect can break off good-sized fragments of the rock she is about to mine, she sets to her arduous undertaking with a bold heart, and it is not long before a tolerable cavity is scooped out. Many of our readers have seen the manner in which human miners proceed when they are forming a hole in a lime or other rock, for the purpose of blasting, and must have noticed that they are in the habit of using a little water, in order to facilitate the boring operation. We are all, also, familiar with the tale of Hannibal chemically softening the Alpine rocks by means of vinegar. The little insect in question has been instructed by the great Creator also to adopt a means of shortening her labour, for it has been observed that she moistens the rock by letting fall a drop or two of fluid upon it from her mouth. By this means her work goes on rapidly. The rubbish soon begins to accumulate. It will be scarcely conjectured what this patient labourer does with it. Were we to look narrowly at the sand-bank which such wasps frequent, we should find on its surface a number of curious little projections like horns, rising from the surface. These are towers built by the sand-wasp of the pieces of rubbish which she scoops out of her mine. She cements them together, and, instead of throwing them away, she lays the masses in regular order until they have assumed the appearance here shown. It has been supposed she does this with a view to keep out enemies and to keep her progeny cool; just as in a tall house the cellar is its coolest apartment, so the height of the tower in question seems to be an additional protection against the rays of the scorching sun. After it has deposited its egg at the bottom of the excavation, the sand-wasp sets out on a foraging expedition, and hunts about until she finds certain green caterpillars. Seizing upon one of these she flies with it to her mine, and then returns for more prey. After collecting about a dozen of these helpless beings, fixing them so that they are hopeless captives inside her dark prison, she bids farewell to the egg, for the future well-being of which she has thus assiduously provided. She takes down her tower of stones, and, with the materials which composed it, fills up the entrance to the cell, thus shutting in both the prisoners and their future devourer in a common dungeon, there to await the changes which time will inevitably bring about.