Pteromalus sp. (?) (Plate [III]., fig. 9).
This little insect was reared, in company with thirteen others of the same species, from a pupa of Eurigaster marginatus which had been procured from a larva of Œceticus omnivorus, and is consequently a true hyperparasite.[[3]] Its curious habits will be better understood by the reader after perusal of the life-histories of those two insects, which I have given on pages [60] and [74]. The method by which the females of the Hymenoptera whose larvæ are parasitic on insects inhabiting other insects, introduce their eggs into their hosts,[[4]] is not at present known to entomologists, but it seems at least probable that they are deposited in the eggs of the parasitic Dipteron before these gain access to the caterpillar of the moth.
Family Ichneumonidæ.
Ichneumon sollicitorius (Plate [III]., fig. 6).
This is the most abundant of our ichneumon-flies, and may be taken amongst herbage from August till May. Its larva is parasitic in the caterpillars of various Noctuæ, having occurred in the following species: Mamestra composita, M. mutans, and M. ustistriga. The pupa may be frequently discovered inside that of the moth, and is quite white in its early stages, but as age advances all the colours of the future insect can be seen through the thin pellicle which invests it. The perfect insect makes its escape through a circular hole, which it drills in the upper end of the unfortunate moth pupa it has destroyed. The sexes of all ichneumon-flies may be at once recognized by the females possessing an ovipositor[[5]] differing considerably in length among the various species, but nearly always plainly visible.
Family Ichneumonidæ.
Ichneumon deceptus (Plate [III]., fig. 7).
This conspicuous insect is chiefly mentioned on account of a very curious habit possessed by the females of congregating in large numbers on matai trees, as many as fifty or sixty specimens being often found huddled together under a single flake of the bark. The males are occasionally taken flying in the open, but I have never seen any amongst these large assemblages of females. Whether the ichneumons are parasitic on some insect which lives on the matai, or whether they assemble to feast on the sweet juice occasionally exuded from its bark, it is impossible to say, but in either case the complete absence of males is a very remarkable circumstance.
Family Ichneumonidæ.
Scolobates varipes (Plate [III]., fig. 8).