Tunnel Entrance to the Dwelling.
We have already found occasion to treat of the snow-house, or igloo, of the Esquimaux, and have now to speak of a subsidiary, though necessary, part of Esquimaux architecture.
Perhaps the reader may have been unfortunate enough to travel by rail in the depth of winter, and to be associated with fellow-passengers who will insist on closing every window, even though the carriage be crowded. Suppose that on such a day, the weather being perfectly fine, the train stops at a station, and the guard outside opens the door to see if another passenger can be accommodated with a place.
No sooner is the door opened than a shower of snow at once fills the carriage. This is simply the moisture suspended in the air and generated by human lungs. The rush of cold air at once freezes this moisture and converts it into snow, thus showing those who will condescend to learn, that they have been breathing and re-breathing the air that has passed through a variety of human lungs, and is charged with their different moistures. I have seen the same phenomenon at a dinner party, where, after the withdrawal of the ladies, one of the windows was opened.
Now, in Esquimaux-land, it is absolutely necessary to conserve every atom of heat, for the cold is so intense that if a cask of water be near a coal fire, only the part next the fire will be thawed, the rest being ice. Cold, therefore, is a foe which has to be fought and kept away from the household. Then there are other foes—such as Polar Bears, for instance—which would be only too glad to get into an igloo and make a meal of its inhabitants. The Esquimaux architect, therefore, avails himself of an ingenious device by which he can set both foes at defiance.
In summer-time he contents himself with a hut made of skins, and merely hangs a skin over the entrance by way of a door. But in the winter, when he is driven to his snow-house for shelter, he acts in a very different manner. Instead of merely cutting an aperture for a door in the side of the igloo, he constructs a long, low, arched tunnel, so small that no one can enter the igloo except by traversing this tunnel on his hands and knees. Sometimes a number of huts are connected with each other, one or two tunnels leading into the air, and the rest serving merely as passages from one hut to the other.
In Nature are several examples of tunnels constructed on the same principle.
There are, for instance, the curious nests of the Fairy Martin of Southern Australia (Hirundo Ariel), which bear a singular resemblance to oil-flasks, the body of the nest being rather globular, and the only entrance being through a tolerably long, tunnel-like neck.
Then there are the various Weaver-birds of Africa, with their long-necked nests. Some of these strange edifices look almost like horse-pistols suspended by the butt, so round is the nest, and so long and narrow is the tunnel-like entrance.
Passing to the insect world, we find the same principle carried out by the now familiar Mason-wasp (Odynerus murarius), some of whose nests are represented in the illustration.
This insect makes a burrow, and at the bottom of it deposits an egg, together with a number of little caterpillars on which the grub, when hatched, will feed. The mother Wasp is not allowed to pursue this task without taking precautions against the admission of enemies to her burrow, especially the ichneumon-flies. As may be inferred from its popular name, the Sand-wasp always selects a sandy spot for its burrow, and generally chooses a piece of tolerably hard sandstone, which it is able to bite into little pellets, aided by a kind of liquid which it secretes.
The following account of the manner in which the Mason-wasp forms and defends its home is taken from the invaluable “Insect Architecture,” by Rennie.
The author begins by describing the form and depth of the burrow, and the soil in which it is made. He then proceeds to show the wonderful manner in which the mother Wasp purveys food for the use of her future young whom she will never see. Guided by instinct, she places in the burrow exactly the number of caterpillars which the young Mason-wasp will have to consume before it attains its perfect condition. It is believed that she partially paralyzes them with her sting before placing them in the burrow. At all events, when they are once packed away, they never move, so that the tiny Wasp grub can feed upon them quite at its leisure.
Here is Rennie’s account of the Sand-wasp and her burrow-making:—
“When this wasp has detached a few grains of the moistened sand, it kneads them together into a pellet about the size of one of the seeds of a gooseberry.
“With the first pellet which it detaches, it lays the foundation of a round tower, as an outwork, immediately over the mouth of its nest. Every pellet which it afterwards carries off from the interior is added to the wall of this outer round tower, which advances in height as the hole in the sand increases in depth. Every two or three minutes, however, during these operations, it takes a short excursion, for the purpose probably of replenishing its store of fluid wherewith to moisten the sand. Yet so little time is lost, that Réaumur has seen a mason-wasp dig in an hour a hole the length of its body, and at the same time build as much of its round tower.
“For the greater part of its height this round tower is perpendicular, but towards the summit it bends into a curve, corresponding to the bend of the insect’s body, which, in all cases of insect architecture, is the model followed. The pellets which form the walls of the tower are not very nicely joined, and numerous vacuities are left between them, giving it the appearance of filigree-work.
“That it should be thus slightly built is not surprising, for it is intended as a temporary structure for protecting the insect while it is excavating its hole, and as a pile of materials, well arranged and ready at hand, for the completion of the interior building,—in the same way that workmen make a regular pile of bricks near the spot where they are going to build. This seems, in fact, to be the main design of the tower, which is taken down as expeditiously as it has been reared.
“Réaumur thinks, that by piling in the sand which has previously been dug out, the wasp intends to guard its progeny for a time from being exposed to the too violent heat of the sun; and he has sometimes even seen that there were not sufficient materials in the tower, in which case the wasp had recourse to the rubbish she had thrown out after the tower was completed. By raising a tower of the materials which she excavates, the wasp produces the same shelter from external heat as a human being would who chose to inhabit a deep cellar of a high house.
“She further protects her progeny from the ichneumon-fly, as the engineer constructs an outwork to render more difficult the approach of an enemy to the citadel. Réaumur has seen this indefatigable enemy of the wasp peep into the mouth of the tower, and then retreat, apparently frightened at the depth of the cell which she was anxious to invade.”
It is no wonder that the Sand-wasp should be so anxious to insure the safety of her nest, for her foes are multitudinous. Putting aside the ordinary Ichneumon-flies, we have the predatory Tachinæ, which are always hovering over such nests, and trying to deposit eggs therein. For many years I have been in the habit of receiving letters from novices in entomology, wanting to know whether I am aware that the common Housefly is in the habit of acting as a parasite. Of course, the writer has mistaken the Tachina for a house-fly, but I cannot regret the fact that some one has really begun to observe Nature, and not only to read books.