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. [Illustration: Fig. 371.--Philanthus triangulum.] [Illustration: Fig. 372.--Mutilla Europæa, male and female.] 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. [Illustration: Fig. 373.--A species of Pimpla.] [Illustration: Fig. 374.--A species of Ophion.] 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.