Crabro leucostomus has been observed by Fletcher to form cells for its larvae in the soft wood of broken willows: the food stored therein consists of two-winged flies of the family Dolichopodidae. This Crabro is parasitised by an Ichneumonid of the genus Tryphon, and by a two-winged fly of uncertain genus, but belonging to the family Tachinidae. The metamorphoses of Crabro chrysostomus have been briefly described by Verhoeff: the food stored consists of Diptera, usually of the family Syrphidae; the larva spins an orange-red cocoon, passes the winter therein, and assumes the pupal form in the spring; there is, he says, a segment more in the female pupa than there is in the male.
The species of the sub-genus Crossocerus provision their nests with Aphididae, but C. wesmaeli makes use, for the purpose, according to Ferton, of an elegant little fly of the family Tipulidae; according to Pissot this same wasp also makes use of a species of Typhlocyba, a genus of the Homopterous division of Rhynchota. Supposing there to be no mistake as to this latter observation, the choice of Diptera and of Homoptera by the same species indicates a very peculiar habit.
Fertonius (Crossocerus) luteicollis in Algeria forms cells at a slight depth in sandy soil, and provisions them with ants. The ant selected is Tapinoma erraticum, and the individuals captured are the wingless workers. The mode of hunting has been described by Ferton; the wasp hovers over one of the ant-paths at a distance of a few millimetres only above the surface, and when an ant that is considered suitable passes, the Fertonius pounces on it, stings it, and carries it off to the burrow; forty or fifty ants are accumulated in a cell, the egg is laid in the heap of victims about one-third of the depth from the bottom; the resulting larva sucks the ants one by one, by attaching itself to the thorax behind the first pair of legs. There is a very interesting point in connection with the habits of this species, viz. that the ants are not only alive, but lively; they have, however, lost the power of co-ordinating the movements of the limbs, and are thus unable to direct any attack against the feeble larva. Ferton thinks there are three generations of this species in a single year.
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Note.—In a note on p. [99] we have mentioned the new publication of Mr. and Mrs. Peckham on the habits of Fossores. We may here add that it contains much fresh information on these Insects, together with criticisms of the views of Fabre and others. One of the points most noteworthy is that they have observed Crabro stirpicola working night and day for a period of forty-two consecutive hours. They made experiments on Bembex spinolae with a view of ascertaining whether the female provisions two nests simultaneously; as the result they think this improbable. If the female Bembecid make nests only consecutively, it is clear it must have but a small fecundity. The larval life extends over about fifteen days; and if we allow three months as the duration of life of a female, it is evident that only about six young can be produced in a season.
CHAPTER IV
HYMENOPTERA ACULEATA CONTINUED—DIVISION IV. FORMICIDAE OR ANTS
Division IV. Heterogyna or Formicidae—Ants.
The segment, or the two segments, behind the propodeum, either small or of irregular form, so that if not throughout of small diameter, the articulation with the segment behind is slender, and there is great mobility. The trochanters undivided. The individuals of each species are usually of three kinds, males, females and workers; the latter have no wings, but the males and females are usually winged, though the females soon lose the flying organs. They live in communities of various numbers, the majority being workers. The larvae are helpless maggots fed and tended by the workers or by the female.
