Up to recent years the Cerceris was considered to act with as much certainty as the Sphex, and to obey an infallible instinct which always guided it for the best in the interests of its offspring. The insects it attacks belong to the genus Buprestis. It consumes them in considerable numbers. Its manner of action, as described by Léon Dufour,[76] much resembles that of the Sphex, and it would be superfluous to describe it. The only fact which I wish to mention, and which has been put out of doubt by the illustrious naturalist, is this: the Buprestis are paralysed, not dead; all the joints of the antennæ and legs remain flexible and the intestines in good condition. He was able to dissect some which had been in a state of lethargy for at least a week or a fortnight, although, under normal conditions, these insects in summer decay rapidly, and after forty-eight hours cannot be used for anatomical purposes. Another observer, Paul Marchal, took up this question afresh, and the results which he obtained seemed to indicate an instinct much less firm than earlier studies tended to show.[77]
Genera less skilful in the art of paralysing victims. — These researches show us that in the Cerceris instinct is still subject to defect. In some neighbouring genera we can seize it, as it were, in process of formation. The way in which the Bembex, or Sand Wasp, provisions burrows by maternal foresight is much less mechanical than that of the Sphex. It is again Fabre who has described with most care the customs of this hymenopterous insect.[78] It hollows out for each egg a chamber communicating with the air by a gallery, and performs this work with little care and very roughly. Less skilful than the others, it does not amass at once all the provisions which its larvæ will need during the period of evolution. When the offspring has absorbed the last prey brought, it is necessary to bring a new victim. This insect is scarcely more advanced than birds, who feed their young from day to day. And it is a great labour to re-open every time the gallery which leads to the nursery; on all these visits, in fact, the Bembex fills it up on leaving, and causes the disappearance of all revealing traces. It is obliged to take so much trouble, because it has not inherited from its ancestors the receipt for the paralysing sting; it throws itself without care on its victim, delivers a few chance blows, and kills it. Necessarily it cannot, under these conditions, lay up provisions for the future; they would corrupt, and the larvæ would not be benefited; hence the obligation of frequently returning to the nest, and of a perpetual hunt to feed descendants whom nature has gifted with an excellent appetite. According to the age of the offspring, the mother chooses prey of different sizes; at first she brings small Diptera; then, when it has grown, she captures for it large blow-flies, and lastly gadflies.[79] It will be seen, then, that if we suppose the instinct of the Sphex to be slowly developed by being derived from a sting given at random, we make a supposition which is quite admissible and rests on ascertained facts. However this may be, the Bembex, returning to its burrow, is able to find it again with marvellous certainty, in spite of the care taken to hide it by removing every trace that might reveal its existence. It is guided by an extraordinary topographic instinct, which men not only do not possess, but cannot even understand the nature of.
It would appear that certain Hymenoptera, fearing to kill their victim with the sting, and not knowing the art of skilful lesions, attempt to immobilise them by wounds of another sort. This is the case with the Pompilius, according to Goureau,[80] who has studied it. This insect nourishes its larvæ with spiders; it seems certain that in most cases the spider is not pricked. Victims who have been taken from the interior of provision burrows can live for a long time in spite of their wounds; they cannot, therefore, have received venom by inoculation. The author already quoted believes that the Pompilius seizes its captive by the pedicle which unites the abdomen to the cephalothorax, and that it triturates this point between its jaws. From this either death or temporary immobility may follow. The Pompilius also makes up for its relative ignorance by considerable ingenuity. Thus sometimes, when it fears a return to life of the victim destined for its larvæ, it cuts off the legs while it is still passive. Goureau has found in the nest of this insect living spiders with their legs cut off.
CHAPTER VI.
DWELLINGS.
ANIMALS NATURALLY PROVIDED WITH DWELLINGS — ANIMALS WHO INCREASE THEIR NATURAL PROTECTION BY THE ADDITION OF FOREIGN BODIES — ANIMALS WHO ESTABLISH THEIR HOME IN THE NATURAL OR ARTIFICIAL DWELLINGS OF OTHERS — CLASSIFICATION OF ARTIFICIAL SHELTERS — HOLLOWED DWELLINGS — RUDIMENTARY BURROWS — CAREFULLY-DISPOSED BURROWS — BURROWS WITH BARNS ADJOINED — DWELLINGS HOLLOWED OUT IN WOOD — WOVEN DWELLINGS — RUDIMENTS OF THIS INDUSTRY — DWELLINGS FORMED OF COARSELY-ENTANGLED MATERIALS — DWELLINGS WOVEN OF FLEXIBLE SUBSTANCES — DWELLINGS WOVEN WITH GREATER ART — THE ART OF SEWING AMONG BIRDS — MODIFICATIONS OF DWELLINGS ACCORDING TO SEASON AND CLIMATE — BUILT DWELLINGS — PAPER NESTS — GELATINE NESTS — CONSTRUCTIONS BUILT OF EARTH — SOLITARY MASONS — MASONS WORKING IN ASSOCIATION — INDIVIDUAL SKILL AND REFLECTION — DWELLINGS BUILT OF HARD MATERIALS UNITED BY MORTAR — THE DAMS OF BEAVERS.
Animals construct dwellings either to protect themselves from the cold, heat, rain, and other chances of the weather, or to retire to at moments when the search for food does not compel them to be outside and exposed to the attacks of enemies. Some inhabit these refuges permanently; others only remain there during the winter; others, again, who live during the rest of the year in the open air set up dwellings to bring forth their young, or to lay their eggs and rear the offspring. Whatever the object may be for which these retreats are built, they constitute altogether various manifestations of the same industry, and I will class them, not according to the uses which they are to serve, but according to the amount of art displayed by the architect.
In this series, as in those which we have already studied, we shall find every stage from that of beings provided for by nature, and endowed with a special organ which secretes for them a shelter, up to those who are constrained by necessity to seek in their own intelligence an expedient to repair the forgetfulness of nature. These productions, so different in their origin, can only be compared from the point of view of the part they play; there are analogies between them but not the least homology.
Animals naturally provided with dwellings. — Nearly all the Mollusca are enveloped by a very hard calcareous case, secreted by their mantle: this shell, which is a movable house, they bear about with them and retire into at the slightest warning.
Caterpillars which are about to be transformed into chrysalides weave a cocoon, a very close dwelling in which they can go through their metamorphosis far from exterior troubles. It is an organic form of dwelling, or produced by an organ. It is not necessary to multiply examples of this kind; they are extremely numerous. In the same category must be ranged the cells issuing from the wax-glands which supply Bees with materials for their combs in which they enclose the eggs of the queen with a provision of honey.