PURSUED BY DRIVER ANTS
The greatest beasts of the forest will fly before these terrible little insects,
one of which is shown in the left-hand corner.
A more remarkable sight even than an ant-bridge is perhaps an ant-nest, by which I mean, not an ants’ nest in the ordinary sense of the term, but a nest made of ants. The following quotation from the much-containing Naturalist in Nicaragua, page 25, will explain this hard saying. “They make their temporary habitations in hollow trees, and sometimes underneath large fallen trunks that offer suitable hollows. A nest that I came across in the latter situation was open at one side. The ants were clustered together in a dense mass like a great swarm of bees hanging from the roof, but reaching to the ground below. Their innumerable long legs looked like brown threads binding together the mass, which must have been at least a cubic yard in bulk, and contained hundreds of thousands of individuals, although many columns were outside, some bringing in the pupæ of ants, others the legs and dissected bodies of various insects. I was surprised to see in this living nest tubular passages leading down to the centre of the mass, kept open just as if it had been formed of inorganic materials. Down these holes the ants who were bringing in booty passed with their prey.” Of the many curiously constructed or strangely produced dwellings of ants, this made out of their own bodies is amongst the most remarkable.
Many ants live in the interior of various plants. The plant generally benefits as much as the insect by this arrangement, so that there is a mutual dependence between the two, which in some cases is carried to such an extent that the life of one or both seems a necessary part of that of the other. In Borneo, for instance, a certain large tuber which grows on the branches of aged trees is always found inhabited by a certain red ant, of small size, but fierce disposition, which rushes out and attacks anyone who ventures at all near its dwelling. The seed of this tuber is disseminated in the same way as is our own mistletoe, through the agency of birds, that is to say, the seed being surrounded by a similar pulpy mass, which adheres to the branch on which it falls. Soon after germination the tuber, which is shaped something like a carrot, begins to develop, but whilst still quite small its growth ceases and in this state it would remain, and before long, die, if it should not happen to be found by the ants in question. If it should be, however, its life is assured. They immediately bore a hole at the base of the stem, upon which this enlarges to a great degree, so that soon there is room for them to excavate galleries in the cellular tissue of the interior, and to form a populous colony. The whole tuber is soon perforated in all directions, and becomes a living and growing formicarium, the great accretion of cellular tissue which has made this possible having been caused by the poison—if we may call it so—of the ant’s bite, in the same way as the sting of the gall-fly raises galls upon the oak.[[80]] Of course, from the moment that the ants appear the tuber is safe from any other insect, or small bird, or mammal that might otherwise do it harm. The ants in defending their nest would defend it, and it is on this principle of mutual advantage that such ant and plant alliances have been brought about.
Thus the dry, arid plains, called savannahs, of tropical America support a species of acacia of which the thorns, characteristic of the family, grow in pairs and are shaped exactly like the horns of some oxen. Every pair of these horns becomes in time an ants’ nest, and if the tree be touched or shaken, the ants rush out full of fury in defence of their habitations. Thus every tree is tenanted by a large army of retainers, who almost more than the thorns themselves, which have been developed for the same purpose, protect it against browsing quadrupeds. Its thorns, however, would be no protection against the leaf-cutting ants in search of materials for their mushroom-beds, whereas these are kept at bay by a hostile species, smaller indeed, but armed with a powerful sting. “For these services,” says Belt, “the ants are not only securely housed by the plant, but are provided with a bountiful supply of food; and to secure their attendance at the right time and place, this food is so arranged and distributed as to effect that object with wonderful perfection. The leaves are bi-pinnate (double, that is to say), and at the base of each pair of leaflets, on the mid-rib, is a crater-formed gland, which, when the leaves are young, secretes a honey-like liquid. Of this the ants are very fond; and they are constantly running about from one gland to another to sip up the honey as it is secreted. But this is not all; there is a still more wonderful provision of solid food. At the end of each of the small divisions of the compound leaflet there is, when the leaf first unfolds, a little yellow, fruit-like body, united to it by a point at its base. Examined through a microscope, this little appendage looks like a golden pear. When the leaf first unfolds the little pears are not quite ripe, and the ants are continually employed going from one to another examining them. When an ant finds one sufficiently advanced it bites the small point of attachment; then, bending down the fruit-like body, it breaks it off and bears it away in triumph to the nest. All the fruit-like bodies do not ripen at once, but successively, so that the ants are kept about the young leaf for some time after it unfolds. Thus the young leaves are always guarded by the ants; and no caterpillar or larger animal could attempt to injure them without being attacked by the little warriors.” Thus, as Mr. Belt very aptly puts it, “the ants are really kept by the acacia as a standing army to protect its leaves from the attacks of herbivorous mammals and insects.”[[81]]
As for the honey or honey-pot ants, they were first heard of in America, and various floating stories, which seemed more or less hard to credit, having got into circulation about them, without there being any positive knowledge to check them, Dr. McCook, to remove this grave reproach to transatlantic entomology, started off one day to observe them. He soon found that the main fact which had been stated was correct, viz. that a certain sect or caste of these ants, disregarding the Italian warning, were in the habit of making themselves all honey, to be swallowed in consequence by the rest of the community. These are the so-called honey-pots, and so well do they deserve their name, that when full the abdomen becomes almost perfectly circular, like a glass globe, and so enormously swollen that the body in proportion to it is like a grain of wheat stuck into a cherry or gooseberry.[[82]] The legs dangle towards the ground, but hardly, or only by a great effort, reach it, and in this last state of distension the insect may find it impossible to get about, though as a rule by dragging or pushing herself along sideways, she is able to do so to a certain extent. These honey-jars have special chambers for their accommodation, and here they hang in clusters from the roof, awaiting the visit of any worker, who upon signifying his wants—it would seem after climbing up to them—is fed, after the ordinary ant manner, by regurgitation. In the same way the honey-bearers are themselves filled, or more properly speaking, feed themselves, since the mouth arrangement, in spite of the direction in which things seem hastening, has not yet become so simple as in the case of a real jar.