I shall not enumerate here all the various ichneumon flies which benefit agriculture, but simply mention the =Small Cabbage Caterpillar Ichneumon Fly= (_Microgaster glomeratus_), depicted in Fig. 90, which, like its host (the large cabbage white), appears in two generations. The larvæ of the ichneumon fly live in large numbers in the large cabbage caterpillar, and at their last moult acquire minute teeth, with which they bite through the skin of their host; they then leave it to die, and surround themselves with a cocoon close to its dead body. There are, besides, a few small and also some large ichneumon flies which lay their eggs in the pupæ of the cabbage white, so that, _e.g._, in winter many of its angular pupæ, occurring on tree stems and hedges, are found with many small or several large white ichneumon larvæ within them. Family: =Tenthredinidæ= (_Saw_-_flies_). Body thick-set. Abdomen never very long, and united by a broad base to the thorax (Fig. 91). Saw-shaped ovipositor (p. 89), drawn in when not in use, and only protruded during egg-laying. Mandibles strong, the remaining mouth-parts not so well developed. The larvæ are false caterpillars (p. 92); they can usually be recognized by their characteristic attitude, for many of them bend the abdomen very much upwards and forwards, especially when frightened, and when at rest the hinder part of the body is spirally coiled (Fig. 91). The fully developed larva spins a cocoon in which it still remains for a long time in the larval condition, even during the whole winter. It becomes a pupa two or three weeks before the appearance of the perfect insect. There are many larvæ of this kind destructive to woods, but only a few which interest the farmer. Here is included— The =Turnip Saw-fly= (_Athalia spinarum_). _Adult_: Female one-third of an inch long, stretch of wing over two-thirds of an inch; male somewhat smaller. Bright orange or reddish yellow. Head black, thorax and legs with black markings. Wings large. _Larva_: Length may be rather more than two-thirds of an inch. The just-hatched larvæ are almost colourless, but the skin quickly becomes bright green, and after the first moult, dark green to black. Ventral side slate grey. Head shining black. Twelve broad body segments, upon which are many wrinkles of the skin. [Illustration: FIG. 91.—The Turnip Saw-fly (_Athalia spinarum_): adult female and two caterpillars. ]