But this direct warfare by other animals is of small consequence. A more important check on the increase of many Coccids is afforded by the indirect action of minute hymenopterous insects, which make use of them as receptacles for their eggs. This plan is adopted by several Hymenoptera, of the families Chalcididæ, Ichneumonidæ, Proctotrupidæ, &c. They do not devour their prey; they allow it to live that they may live on it. By means of their long ovipositor they pierce its body, and deposit in it an egg. As the victim grows the egg matures, changes into a larva, and still remains in the body of the Coccid; changes again into a pupa, and by this time the Coccid is at liberty to die, for the parasite has no further use for it except as a shelter; then, when the proper time arrives, the perfect fly emerges and departs. All Coccids are by no means equally subject to this system. In the United States, according to Mr. L. O. Howard,[I] parasites are found in nearly all genera--Diaspidinæ, Lecanidinæ, or Coccidinæ. In this country, as far as observation shows at present, the Lecanidinæ are the most liable to attack, some of the Diaspidinæ next, and the Coccidinæ least of all. _Mytilaspis pomorum_, so hurtful to apple-trees, does not seem to be attacked. _Icerya purchasi_, the worst species of all, has not yet furnished a single parasitic fly. A few specimens of _Dactylopius glaucus_ contain parasites; a good many of _Fiorinia asteliæ_ and _F. stricta_; while _Ctenochiton perforatus_ and _C. viridis_ appear to be the favourite victims, as sometimes scarcely any specimens on a plant can be examined which do not contain either a larva or a pupa of a parasite. It is to be observed that in no case is more than one parasite to be found in a Coccid. [I] Report of the Entomologist, U.S. Dep. of Agric., 1880, pp. 350-371. Unfortunately, although this provision of Nature must have a very considerable effect in preventing the increase of Coccididæ, it is subject to two drawbacks. In the first place, as just observed, some of the most injurious pests appear to be unaffected by it. Probably, up to the present time the worst plant-enemies[J] in New Zealand have been _Mytilaspis pomorum_, _Aspidiotus coccineus_, _Aspidiotus camelliæ_, _Lecanium hesperidum_, _Lecanium oleæ_, _Lecanium hemisphæricum_, _Pulvinaria camellicola_, and _Icerya purchasi_. Here reference is made not so much to insects which render plants unsightly as to those which seriously injure its growth: many others, such as _Fiorinia asteliæ_ or _Ctenochiton viridis_ are ugly enough, but have not been destructive. Of the injurious species above named none, apparently, are troubled in this country by parasitic insects up to the present time, at least to any appreciable extent. [J] Speaking of Coccids only; _Kermaphis pini_ is equally, if not more, destructive.