Among the Lasius niger the independence of the workers is perhaps still greater; no doubt they do their best to concert their efforts, but they do not succeed so well as if an inevitable instinct impelled them. Notwithstanding the irregularities of the construction, it is possible to recognise in it a whole formed of hollowed, concentric half-spheres; they have been added one after the other to the surface to increase the dwelling. The interval between these clay spheres constitutes a storey, cut up by the partitions which divide it into chambers and communicating galleries; the roofs of the largest halls are supported by numerous pillars. ([Fig. 40.])
These ants, as Huber has shown, are highly accomplished in the art of constructing a cupola. When they wish to increase their nest by a new layer, they take advantage of the first wet day, the rain serving to agglutinate and unite the materials. They operate in almost the same way as the Formica fusca, though exhibiting more skill and resource as architects; they know better how to calculate beforehand the number of pillars required in a hall of a determined size. As soon as the rain has given the signal for work, they spread themselves abroad and prepare a very thick terrace on the external surface of the dwelling which has become too small. They carry to it small balls of earth ground very fine by their jaws, and then lightly piled up so as to pulverise afresh; these are then spread over the construction with the anterior legs. Then, by hollowing out, the ants trace the plan of the new storey, leaving the walls, partitions, and columns in relief. After having raised these parts to a sufficient height, all work together to cover them with a general ceiling, each ant applying itself to one small corner of the work.
The vaulting is executed by the method already described; horizontal ledges, slanting from the summit of pillar or wall, are formed to meet one another. The insects are intelligent enough to begin their labour at the spots best fitted to give strong support to the overhanging materials, as for instance, at the angle of two walls. There is so much activity among the workers, and they are so anxious to take advantage of the damp, that the storey is sometimes completely finished in seven or eight hours. If the rain suddenly stops in the course of the work, they abandon operations, to complete them as soon as another shower falls.
I have already had occasion to speak of the covered passages and Aphis-pens built by Ants outside their dwellings. Besides these constructions, they also make roads in the fields, tearing up the grass and hollowing out the earth so as to form a beaten path free from the lilliputian bushes in which there would be danger of becoming entangled, on returning to the nest laden with various and often embarrassing burdens.
Nor are Ants by any means alone in exhibiting the results of individual skill and reflection. It will, however, be sufficient to mention only one other example, that furnished by Spiders. McCook, in his great work, after elaborately describing and carefully illustrating the skill exhibited in individual cases by Spiders in their aërial labours, considers himself justified in concluding as follows: — “The manner in which the ends of the radii which terminate upon the herb are wrapped roundabout and braced by the notched zone; the manner in which the wide non-viscid scaffold lines are woven in order to give vantage ground from which to place the close-lying and permanent viscid spirals, upon which the usefulness of the orb depends — all these, to mention no other points, seem to indicate a very delicate perception of those modes (shall I also say principles?) of construction which are continually recognised in the art of the builder, the architect, and the engineer.”[107]
Dwellings built of hard materials united by mortar. — Among mammals few animals have become so skilful in the art of building houses as the insects we have just been considering. There are, however, two who equal if they do not surpass them — the Musk-rat and its relative, the Beaver.
The Musk-rats of Canada live in colonies on the banks of streams or deep lakes, and construct dwellings which are very well arranged. In their methods we find combined the woven shelter with the house of built earth. Their cabins are established over the highest level of the water and look like little domes. In building them the animals begin by placing reeds in the earth; these they interlace and weave so as to form a sort of vertical mat. They plaster it externally with a layer of mud, which is mixed by means of the paws and smoothed by the tail. At the upper part of the hut the reeds are not pressed together or covered with earth, so that the air may be renewed in the interior. A dwelling of this kind, intended to house six or eight individuals who have combined to build it, may measure up to 65 centimetres in diameter. There is no door directly opening on to the ground. A subterranean gallery starts from the floor and opens out beneath the water. It presents secondary branches, some horizontal, through which the animal goes in search of roots for food, while others descend vertically to pits specially reserved for the disposal of ordure.
But it is, above all, the Beaver (Castor fiber) who exhibits the highest qualities as an engineer and mason. This industrious and sagacious Rodent is well adapted to inconvenience the partisans of instinct as an entity, apart from intelligence, which renders animals similar to machines and impels them to effect associated acts, without themselves being able to understand them, and with a fatality and determination from which they can under no circumstance escape.