Microgaster
A genus of parasitic insects belonging to the Braconidae, a family of Ichneumons, very rich in species. They are all of small size, seldom exceeding 1/6in. in length, and 1/4in. in spread of wings. The body-colours are almost always black, red, or yellow; the legs are usually paler, at times almost white. The ovipositor is usually short, and is often hardly visible. The wings are transparent, and show few cross-veins and cells. Some of the Braconidae in the larval state live in the bodies of aphides; others live in the bodies of caterpillars of butterflies and of moths. To this latter group belongs the genus Microgaster. The most noticeable species is M. glomeratus, which is very helpful to gardeners, because of the number of caterpillars of the White Cabbage Butterfly it destroys. The larvae live on the fat of the caterpillars, usually many in each individual; and, till full fed, they do not seen greatly to interfere with the growth of their hosts, as they do not attack any vital organs of the latter. But, when mature, the parasitic larvae eat their way through the skin of their hosts, and each proceeds to spin a small oval, yellow, silken cocoon. These cocoons are frequently grouped in masses of nearly 1in. across, on the dying or dead caterpillars, and must have often been observed by every gardener. The perfect flies have the body deep black, with very short, white hairs; the belly and legs yellow; and the four wings transparent, and covered with short hairs. See also Icheumon Flies.