Elizabeth Grant, Holiday Rambles-Or peeps into the Book of Nature, Londres, G. Routledge & Co., 1857, p.158-166.
“I saw it,” said Helen;” it looked a large one; but what are those little long things, swimming under the leaves of that water lily?”
“Those are little fish,” answered Mrs. Melville. “There appear to be a great number of them.”
“Are there many insects living in the water, mamma?” asked Agnes.
“A great many, my love,” answered Mrs. Melville. “I think the grubs of the caddis-fly are some of the most curious and interesting, from the pains they take to build themselves houses.”
“Oh! mamma,” said Walter, “ please to tell us about them. I like so much to hear the history of insects.”
“I am glad you are interested in what I relate, my dear,” said Mrs. Melville. “ The study of nature has to me always been a very favourite employment. To find out the perfections and instincts of the animal creation around us, is a pleasurable occupation, but one that requires much time and patience. Of this we may be sure, that each production of nature has its proper use, and is made to fill some place in the universe that without it would be void, and thus destroy the harmony of the whole. I will now commence the history of the little worms and their habitations, as Walter is, I see, anxious for the account.”
“We all wish to hear it, mamma,” said Agnes.
“The grubs of the caddis-flies,” continued Mrs. Melville, “live under water, where they construct for themselves moveable tents, of various materials, such as sand, stones, shells, wood, and leaves, which are skilfully joined, and strongly cemented. One kind of these grubs forms a pretty case of leaves glued together lengthwise, but leaving an aperture sufficiently large for the inhabitant to put out its head and shoulders, when it wishes to look about for food.”
“What a funny thing it must look,” said Helen, “with its cloak of leaves. I should like to see one very much.”
“It would be a pleasing sight,” replied Mrs. Melville; “but these little worms live at the bottom of the water, and as we have at present no means of raising them, you must be content with my description. Another species employs pieces of reed, cut into convenient lengths, or bits of grass, straw, or wood, &c., carefully joining and cementing each piece to its fellow, as the work proceeds, and frequently finishing the whole by adding a broad piece, longer than the rest, to shade the door-way overhead, so that the insect may not be seen from above.”
“ That must be a very wise worm, mama,” said Agnes, “ to make a screen for itself whilst securing its prey, for that is why it constructs a lobby to its house, is it not?”
“No doubt but that is the purpose of the little creature, my dear,” replied Mrs. Melville. “In thus framing its habitation it acts according to the instinct for self-preservation given it by its great Creator; for the projection of the straw over its head must hide it from the observation of the creatures above it, and materially add to its security. A more laborious structure is reared by another of these grubs, which weaves together a group of the leaves of plants into a roundish ball, and in the interior of this forms a cell for its abode. Another of these aquatic architects makes choice of the tiny shells of young fresh-water muscles and snails to form a moveable grotto.”
“Are there any fish in these shells?” inquired George.
“Many of them are inhabited,” answered Mrs. Melville; “but that makes no difference to the little builder, for he drags them along without mercy, keeping them close prisoners. These grotto-building grubs are by no means uncommon in ponds. One of the most surprising instances of the skill of these little creatures in the construction of their nests with small stones. The difficulty consists in making a tube about the width of the hollow of a wheat straw, or crow quill, and equally smooth and uniform throughout; the materials used being small stones, full of angles and irregularities, renders this a task of no ordinary magnitude; yet the little architects, by patiently examining the stones, and turning them round on every side, never fail to accomplish their plans. This, however, is not the only difficulty. The under surface of this tube must be flat and smooth, without any projecting angles that might impede the progress of the little animal when dragging its habitation along the bottom of the rivulet in which it resides.”
“Why does it choose to make its nest of stones,” asked Agnes, “ since it has so much trouble to arrange them?”
“Here again,” replied Mrs. Melville, “we may trace the action of that power implanted in the nature of this little insect, by its omnipotent Creator, and notice the evidence of design; for this species lives at the bottom of streams, where, but for the weight of the materials selected for its house, it would be swept away by the current. To keep it from this danger, it is probable the grub makes choice of larger stones than it might otherwise want, and therefore cases are frequently found composed of very small stones and sand, to which, when nearly finished, a large one is added, by way of ballast. In other instances, when the materials are found to be too heavy, a bit of light wood or a hollow straw is attached to the case to buoy it up.”
“How extraordinary it is that the grub should know what things are heavy, and what are light,” remarked Miss St. Clair, “ and should be able to distinguish between the weight of stone and the buoyancy of wood and straws. It is a proof of the wisdom of Almighty God, that He suits the habits of creatures to the situation they occupy; for the parents of this little worm could render it no assistance, they must have quitted their habitation in the water, attained their perfect form, passed their short and happy life, before the egg containing the little insect was hatched.”
“Mamma,” said Helen, “ how does the little grub fasten the stones for its house together?”
“By cement, my love,” replied Mrs. Melville, “that is incapable of being dissolved in water. The grubs themselves are admirably adapted for their mode of life, the portion of their bodies which is always enclosed in the case being soft and tender, while the head and shoulders, which for the most part project beyond the doorway, are firm, hard, and consequently less liable to injury.”
“Do these grubs go through the same transformation as the Dragon-fly?” inquired George.
“They do,” replied Mrs. Melville; “ the grub I have been describing is the larva; so long as it remains in its grub state it can withdraw itself within its case of stones; but when it feels its change approaching, it contrives additional security, by weaving at the entrance of its gallery a grating of its singular silk, which hardens in water and remains indissoluble. The strong threads are made to cross each other, forming a small circular place, perforated with minute holes at regular intervals, which exactly fits the opening, and is place a little within the margin.”
“What are the holes for?” asked Walter.
“They are to enable the little creature to breathe,” replied Mrs Melville, “the holes admit a current of fresh water, which is used by it instead of air. It is also provided with a pair of curved mandibles, with which it is able to make its exit through the grating, and then throws them aside.”
Mrs. Melville having finished the history of the Caddis-fly, they rose to pursue their way to the refreshing shade of the larch wood.