The genus Dolichurus is by some entomologists considered the type of a sub-family allied to the Ampulicides; it long consisted of a small and rare European Insect, but some exotic species have recently been added to it. It will probably prove not sufficiently distinct from Ampulicides, although the pronotum is much shorter, but Handlirsch has recently observed that the European species attacks Blattidae as do the normal Ampulicides; and Ferton has recorded that D. haemorrhous lives at the expense of Loboptera decipiens, the wasp depositing its egg on the left intermediate femur of the prey. This is placed in a solitary cell, and is entirely consumed by the larva, life being preserved till within a few hours of the end of the repast, which occupies altogether eight days.
Sub-Fam. 3. Larrides.—Hind body not pedicellate, or with only a short pedicel; one spur on the middle tibia; labrum inconspicuous. Marginal cell of the front wings appendiculate,[[52]] or mandibles excised externally, or both.
This group is by some writers called Tachytides instead of Larrides, as owing to a change of nomenclature Tachytes may now be considered its principal genus. It is in connection with this and the neighbouring sub-families of Sphegidae that some of the greatest taxonomical difficulties exist. We include in Larrides the "Miscophus group" of Kohl.
The species of the genus Tachytes seem to have habits very similar to those of the genus Sphex; they form shafts in the earth and provision them with Orthoptera; like the Sphex and other Fossores, they have the habit, when they fly to their tunnel with a victim, of depositing it for a short time on the ground close to the mouth of the burrow while they turn round and enter backwards; and, after doing this they again seize their prey and drag it into the burrow. Fabre availed himself of an opportunity to remove the prey while the Hymenopteron was entering the hole alone; as a result it had to come out again to seek the object; this it soon found, and carried to the hole, relinquishing it again as usual while it turned round; Fabre repeated the operation several times, and always with the same result; the wasp, though it might have kept hold of the victim while it turned, and thus have saved itself from losing the precious object, never did so.
One species of Tachytes in the south of France selects as its prey Orthoptera of the family Mantidae, Insects of a highly ferocious disposition, and provided with most powerful front legs, capable of cutting in two by a single act the body of an aggressor like the Tachytes; the latter is, however, by no means dismayed by the arms of its future victim, but hovering above the latter for some time, as if to confuse it, and causing it repeatedly to turn its very mobile head, the Tachytes at last pounces down and instantaneously stings the Mantis in the nerve centre between the formidable arms, which at once are reduced to incapacity; subsequently the Tachytes paralyses each of the other pairs of legs, and then carries off its victim.
Fig. 45.—Tachytes pectinipes ♀. Britain.
Larra anathema chooses mole-crickets as the viand for its young, and Tachysphex panzeri selects grasshoppers of the family Acridiidae. Larra pompiliformis (= Tachytes niger, Fabre) sometimes associates itself with Sphex flavipennis (? S. maxillosus, according to Kohl), forming its burrow amidst the works of a colony of that species, and making use, like the Sphex, of crickets for provender. This led Fabre to believe that the Larra stole its prey from the Sphex, but he has since withdrawn this indictment, and declares that the Larra obtains its crickets by the more honourable, if not more humane, process of catching and stinging them itself. Smith has informed us, on the faith of his own observation, that L. pompiliformis uses both Lepidopterous larvae and grasshoppers for its stores.
T. (Larrada) australis, according to Whittell, plays the part of a burglar, breaking open the cells of Pelopaeus (Sceliphron) laetus after they have been completed and stored with spiders; it then takes possession of the cell, and curiously enough the Pelopaeus permits this, although the cell contains its egg and the store of food that is intended for the use of its own young. To us this seems very strange, but it is probable that the Pelopaeus has no idea of the consequences of the intruder's operations; it being one of the strange facts of nature that these highly endowed creatures never even see the offspring for whose welfare they labour with such extraordinary ingenuity and perseverance. Neither can we suppose that they have a conception of it derived from a knowledge of their own individual history; for their very complete metamorphosis is scarcely reconcilable with any such recollection on their part. It may possibly therefore be the case that, having no idea whatever of the offspring, they are equally destitute of any conception that it will be destroyed by the operations of the Larrada. However this may be, Whittell informs us that both wasps skirmish about for a little as if each were mistrustful and somewhat afraid of the other; this ends by the Pelopaeus withdrawing its opposition and by the Larrada taking possession of the cell, which it then proceeds to divide into two, using for the purpose of the partition portions of the material of the nest itself; possibly it is only a contraction of the size of the cell, not a true division, that is effected; however this may be, after it is accomplished the Larrada deposits its own egg in the cell, having, it is believed by Whittell, previously destroyed that of the Pelopaeus. Judging from what occurs in other species it is, however, more probable that the destruction of the egg or young of the Pelopaeus is carried out by the larva of the Larrada and not by the parent-wasp. From a remark made by Maindron as to the proceedings of Larrada modesta, in Ternate, it seems probable that its habits may prove to be similar to those of L. australis, for it frequents the nests of Pelopaeus after they have been completed.
Sub-Fam. 4. Trypoxylonides.—Differ from Larrides by the inner margin of the eyes being concave, and the marginal cell not appendiculate. (In Trypoxylon there is only one distinct submarginal and one distinct discoidal cell, a second of each being indicated faintly.)