Some of the _Chalcididæ_ are parasitic upon insects in their earliest stages, actually depositing their eggs in those of moths and butterflies. Others are entirely parasitic upon parasites, laying their eggs in the aphidii, which are parasites of the aphis. Some of them haunt the galls, and contrive to make their young parasitic upon the immature cynipidæ which lie within the gall. The common small tortoise-shell butterfly is terribly infested with these little creatures, and we have bred hundreds of the gem-like _Chalcididæ_ from the larvæ and pupæ of that butterfly. One of the _Chalcididæ_, belonging to the genus _Melittobia_, is a parasite upon the _Anthophora_; and the curious part of the proceeding is, that it finds there another parasite, which becomes developed in the home of the bee: the _Melittobia_ feeds indiscriminately upon the bee and parasite. Although the _Melittobia_ does not make such wholesale destruction as is wrought by the earwig when it gets into a nest, it does more damage to the bee, on account of its great numbers. Some three or four females will lay a great quantity of eggs within a nest, and from those eggs a hundred of the young will be developed. When the larvæ are fully grown, they quit their hold of their prey, and fall to the bottom of the cell, where they lie until they have assumed the perfect form. They then burst forth, together with those of the bee that may have escaped their attacks.] An interesting account is given by Réaumur of another mason-bee (_Megachile muraria_), not a native of Britain, selecting earthy sand, grain by grain; her glueing a mass of these together with saliva, and building with them her cells from the foundation. But the cells of the Greenwich Park nest were apparently composed of the mortar of the brick wall; though the external covering seems to have been constructed as Réaumur describes his nest, with the occasional addition of small stones.