All these facts were observed with great exactness in a swarm given in 1874 by M. Drory (who during a long period of years studied every Brazilian species of Melipona at Bordeaux) to the Jardin d’Acclimatation. It was even seen that the door might be put up under certain circumstances in open day, as for example, when a storm or sudden cold delays the appearance of the workers. If one of them happened to be late it had to perforate the partition, and the hole was then stopped up again.
Fortifications of Bees. — As these facts take place always they may be called instinctive; but that is not the case with regard to defences elevated with a view to a particular circumstance, and which disappear when the danger to which they correspond disappears. Such are the labours of the bees to repel the invasions of the large nocturnal Death’s-head Moth. ([Fig. 42.]) He is very greedy of honey, and furtively introduces himself into the hives. Protected by the long and fluffy hairs which cover him, he has little to fear from stings, and gorges himself with the greatest freedom on the stores of the swarm. Huber, in his admirable investigations,[113] narrates that one year in Switzerland numbers of hives were emptied, and contained no more honey in summer than in the spring. During that year Death’s-head Moths were very numerous. The illustrious naturalist soon became certain that this moth was guilty of the thefts in question.
While he was reflecting as to what should be done, the bees, who were more directly interested, had invented several different methods of procedure. Some closed the entrance with wax, leaving only a narrow opening through which the great robber could not penetrate. Others built up before the opening a series of parallel walls, leaving between them a zigzag corridor through which the Hymenoptera themselves were able to enter. But the intruder was much too long to perform this exercise successfully. Man utilises defences of this kind; it is thus at the entrance of a field, for example, he places a turnstile, or parallel bars that do not face each other; the passage is not closed for him, but a cow is too long to overcome the obstacle. In years when the Death’s-head Moth is rare the bees do not set up these barricades, which, indeed, they themselves find troublesome. For two or three consecutive years they leave their doors wide open. Then another invasion occurs, and they immediately close the openings. It cannot be denied that in these cases their acts agree with circumstances that are not habitual.[114]
Precautions against inquisitiveness. — I will finally quote a fact of defence which took place under circumstances that were absolutely exceptional, and which therefore exhibits genuine reflection in these insects. During the first exhibition of 1855 an artificial hive was set up, one face of which was closed by a glass pane. A wooden shutter concealed this pane, but passers-by opened it every moment to contemplate the work of the small insects. Annoyed by this inquisitiveness, the bees resolved to put an end to it, and cemented the shutter with propolis. When this substance dried it was no longer possible to open the shutter. The bees were visible to nobody.
Lighting up the nests. — An improvement of another nature in the comfort of the dwelling is introduced by the Baya, and if the facts narrated are correct they are the most marvellous of all. It is a question of lighting up a nest by means of Glow-worms. The Melicourvis baya inhabits India; it is a small bird related to the Loxia, already spoken of in this book. Like the latter it constructs a nest that is very well designed and executed. ([Fig. 43.]) It suspends it in general from a palm tree, but sometimes also from the roofs of houses. In these shelters, woven with extreme art, are always to be found little balls of dry and hardened clay. Why does the bird amass these objects? Is it impelled by a collector’s instinct less perfect than that of the Bower-bird? There is no reason to suppose this. Nor does it appear that he wishes to make the nest heavier and prevent it by this ballast from being blown about by every breeze when the couple are out, and the young not heavy enough to ensure the stability of the edifice. The part played by these little balls is much more remarkable, if we may trust the evidence of the natives, as confirmed by competent European observers. Thus Mr. H. A. Severn writes: — “I have been informed on safe authority that the Indian Bottle-bird protects his nest at night by sticking several of these glow-beetles around the entrance by means of clay; and only a few days back an intimate friend of my own was watching three rats on a roof-rafter of his bungalow when a glow-fly lodged very close to them; the rats immediately scampered off.”[115] These observations are confirmed by Captain Briant, as reported by Professor R. Dubois.[116]
In tropical regions luminous insects give out a brilliant light, of which the Glow-worms of northern countries can only give a feeble idea. These flying or climbing stars are the constellations of virgin forests. In South America the Indians utilise one of these insects, the Cucujo, by fastening it to the great toe like a little lantern, and profit by its light to find their road or to preserve their naked feet from snakes. The first missionaries to the Antilles, lacking oil for their lamps, sometimes replaced them by Fire-flies to read matins by.[117] The Melicourvis baya had already discovered this method of lighting, and the mysterious little balls of clay were nothing more than candlesticks in which these birds set Glow-worms, when they are fresh, to act as candles. The entrance to the nest is thus luminous. ([Fig. 44.])