Chapter VI: Hymenoptera (4)

The Amazons begin their expeditions at the end of June, during the hottest hours of the day. They come out in long files, eight or ten abreast, preceded by their scouts. These columns start at a run, in a straight line, and without feeling their way. They have no chieftain. The van is re-formed every moment. Those who are in front do not remain there; at the end of a certain time they go and range themselves in the rear, and are replaced by those which were behind. The whole troop is thus in constant communication through its entire length. Rarely does the expedition divide into two bodies. Arrived under the walls of the fortress, the column halts and masses itself into one corps. The assault is made with incredible impetuosity. In the twinkling of an eye the place is escaladed, taken by storm, and pillaged, and the ashy-black ants are either put to flight or led away into captivity. The same ant-hill may be invaded as many as three times running on the same day; but then the ashy-black ants, on their guard, have barricaded themselves in, and in that case the aggressors return home without pillaging them.

The Mining Ants (Fig. 370) are less timid than the ashy-black; and, as they defend themselves with more energy, there are frequently deadly combats, and the field of battle is left covered with heads, legs, and limbs, scattered about here and there with the dead and wounded. The miners pursue the pillagers, and snatch their plunder from them. But they are sometimes driven back vigorously, and the russet ants gain their lair with the plunder.

The tactics of the Red Ants (_Formica sanguinea_) differ from those of the russet. They only sally forth in small detachments, which begin by engaging in skirmishes with the scouts thrown out round the enemy's ant-hill. Couriers, despatched from time to time to the camp of the red ants, bring up reinforcements. When the troop feels itself sufficiently strong, it invades the nest of the ashy-black ants, and carries off their offspring, which the latter have not had time to secure. Sometimes, also, the red ants instal themselves in the nest whose inhabitants they have ejected, and transfer their own population to it. The motive for this emigration is that the old nest has become useless, or that it is exposed to some danger. The red ants are not the only ants which thus desert their birth-place. Many species abandon it likewise, for analogous motives, and construct elsewhere another dwelling, to which they transport all the population of the first nest.

When we reflect on the habits of ants, we are forced to admit that intelligence and reason appear still more in their acts than in those of bees. The life of ants, as well as that of bees, as far as we are concerned, is an unintelligible enigma. The acts of animals, in general, are sometimes an abyss unfathomable to our reason. The Orientals say, "The last word may be written on man: on the elephant, never!" Let us add that they should no more say that the elephant will be an inexhaustible theme, but that the history of the ant will continue so always.

The best-known genera of the Fossores, or Fossorial Hymenoptera, are _Philanthus_ (Fig. 371), which feeds its larvæ on bees, having first numbed them by its sting; _Pompilus_ and _Sphex_, which attack spiders; and _Mutilla_ (Fig. 372), whose females resemble ants, being variegated with red and yellow, the males, being provided with wings and smaller in size, and black. The _Mutillæ_ are parasitical on solitary bees, their larvæ devouring their larvæ.

Other Hymenoptera lay their eggs under the skin of certain insects, especially when these are in the larva or caterpillar state, thus rendering service to agriculture by destroying a great number of noxious insects. In lieu of a sting they have an auger, intended to pierce the skin of their victims. It is thus that the _Ichneumons_ introduce their eggs under the skin of caterpillars. The _Pimplas_ (Fig. 373), which belongs to this group, have a very long ovipositor, which, with its two appendages, constitute three lancets, and enable them to get at the larvæ in their retreats. The _Ophions_ (Fig. 374) have a sickle-shaped abdomen. They lay their eggs on the skin of caterpillars, which they attack with the short cutting auger with which they are provided.

The _Cynips_, or Gall-insects, are small black or tawny Hymenoptera, the females of which have an auger, rolled up spirally and hidden in a fissure of the abdomen, with which they prick the young shoots of plants. A peculiar liquid which they pour into the hole round the egg they have laid, causes an excrescence to grow, which is called a "gall." The larva is developed in the centre of this gall, and transformed into a pupa; and afterwards into a perfect insect, which makes its exit by a hole in the wall of its prison. Fig. 375 represents the Cynips of the oak tree (_Cynips quercusfolii_), and Figs. 376 and 377 the galls it produces. The galls of the rose are hairy, and are sometimes called "Robin's Cushion." The gall-nut, rich in tannin, which is used in the manufacture of ink, is the produce of a foreign Cynips, which lives on an oak found in the East. Apples of Sodom, which travellers bring back from the shores of the Dead Sea, are large galls[106] full of dry dust and larvæ.

[106] Made by _Cynips insana_.--ED.

The _Urocerata_ and the _Tenthredinetæ_ form two tribes of insects, of which the first are of great size, have a cylindrical body, the abdomen being attached to the thorax in its whole breadth, without any pedicle.

The insects of the genus _Sirex_ (Fig. 378), belonging to the former of these, lay their eggs in living wood, and their larvæ live for many years in the interior. They are to be met with in great numbers in forests of pine trees, and, according to Latreille, show themselves sometimes in such great numbers as to become an object of terror. The female of the Giant Sirex (_Sirex gigas_) possesses a long rectilinear auger. The mandibles of the larvæ are of great strength, and are even capable of perforating lead. This fact has been observed many times. In 1857 Marshal Vaillant presented to the Académie des Sciences some packets of cartridges containing balls which had been pierced through by the larvæ of the Sirex during the sojourn of the French troops in the Crimea. Some of these insects were still shut up in the gallery which they had hollowed out in the metal. M. Dumeril (and this was one of the last works of that venerable and learned naturalist) wrote a Report on this subject, in which were recorded many analogous instances. He quoted, as an example, that M. le Marquis de Brême, in 1844, showed to the Société Zoologique many cartridges in which the balls had been perforated by the insects to a depth of about a quarter of an inch. These cartridges came from the arsenal of Turin. They had been placed in barrels made of larch wood, the inside of which had been attacked by the insects. It was discovered that it was after having left the wood that they had gnawed through the envelopes of the cartridges, and at last into the balls themselves. In 1833 Audouin presented to the Société Entomologique de France a plate of lead, from the roof of a building, on which this naturalist supposed that the larvæ of a _Callidium_[107] had made deep sinuosities, as they do in wood. Before this, parts of the leaden roofs at La Rochelle had been noticed not only gnawed, but pierced from one side to the other, by the larvæ of _Bostrichus capucinus_.[108] In 1844 M. Desmarest reported the erosion and perforation of sheets of lead by a species of _Bostrichus_ and by _Callidium_. In 1843 M. Du Boys presented to the Société d'Agriculture of Limoges some stereotyped plates--composed, as is well-known, of a very hard alloy, formed of antimony and lead--which had been pierced and riddled with holes by two specimens of a _Bostrichus_. The holes were a seventh of an inch in diameter by two inches in depth. The stereotypes were thus perforated, although they had been wrapped up in many folds of paper and cardboard. As the printing served for a work called "Les Fastes Militaires de la France," one may say that the brave soldiers received from an insect more wounds than their enemies had ever given them.

[107] A coleopterous insect.--ED.

[108] Also a beetle.--ED.

To prove that these insects have really the power to perforate metals as others perforate and pass through woody matter, the entomologist of Limoges made the following experiments. He placed in a leaden box, the sides of which were thin, a living specimen of the Fire-coloured Lepture of Geoffroy (_Callidium sanguineum_), a Coleopteron which is commonly found in houses in France in winter, its larvæ being developed in great numbers in firewood. Above this box he fitted on another, also containing a specimen of this insect, which he shut in with a third box. A few days afterwards he separated the boxes. The middle one had been pierced through, and the two insects were found together, the one which was below having made a hole through which it might introduce itself into the middle box. M. Du Boys made a chemical experiment which enabled him to establish beyond a doubt that the insect which had gnawed the metal had not made it serve as its food. The dried body of one of these insects was analysed. After having immersed it in nitric acid it was completely burnt, and there could not be found in the ashes acted upon by the nitric acid the least trace of lead. This experiment proves that these insects had for their object only to escape from the galleries in which they were accidentally deposited in their larva state, and that it was not until they had undergone their complete transformation that they endeavoured to gain their liberty. Observations of the same kind were multiplied after the Report of M. Dumeril. The Académie des Sciences received, in the month of June, 1861, two Memoirs--one from M. Heriot, captain of artillery, the other from M. Bouteille, curator of the Museum of Natural History of Grenoble--containing many new observations on the perforation by insects of leaden balls contained in cartridges prepared for war. M. Milne-Edwards read to the Académie des Sciences a short Report on these works.

The insect which had produced the perforations observed in the balls sent to the Crimea in 1857, and which M. Dumeril particularly studied, was the _Sirex juvencus_, and had been taken from France in the wood forming the boxes which contained the cartridges. In the other case of which we are speaking, that is to say, of the cartridges which were sent in 1861 to the Académie by Captain Heriot and by M. Bouteille, the perforations had been produced by other species. M. Milne-Edwards, who found the insect that had caused this strange damage, had no trouble in recognising it as the _Sirex gigas_, which, in its larva state, lives in the interior of old trees or pieces of wood, and which, after it has gone through all its metamorphoses, comes out of its retreat to reproduce its kind. To clear themselves a passage, they cut away with their mandibles the ligneous substances or other hard bodies they meet with on their road. It was in pursuing this object that the insects, imprisoned accidentally in the packets of cartridges when they were yet only in the larva state, must have attacked the leaden balls, as also the paper and the other matters which they met with on their road, and which opposed their passage. M. Bouteille proves, in his Memoir, that M. Dumeril has committed an error in saying that the perforating organ employed by the _Sirex_ to attack the leaden balls in the cartridges in the Crimea was the auger situated at the extremity of the abdomen of the female, and intended for cutting into that part of the wood where it is to lay its eggs. M. Bouteille has established, in fact, that they were not only the females which attacked the cartridges, but that the males, which have no auger, had occasioned the same damage.

The _Tenthredinetæ_ are called "Saw-Flies," because the females are furnished with a double auger, notched like a saw, with which they cut into the branches in which they lay their eggs. The larvæ of these insects have a striking resemblance to the caterpillars of Lepidoptera. They can only be distinguished from them by a great globular head, not hollowed out, and by their abdominal legs, in general to the number of more than ten. They are called false caterpillars (Fig. 379). Most of them, when touched, erect themselves and move about in a threatening manner. They spin a silken cocoon before changing into pupæ. The _Lophyrus pini_, which devours the leaves of pine trees, belongs to this family.