This creature lays its eggs in the body of the cabbage caterpillar, forty or fifty eggs being deposited in the same larva. They soon hatch into little transparent grubs, which lie under the skin, and live on the fatty parts of the caterpillar, which continues to grow, and seems to thrive, whereas its bulk is largely made up of the ichneumon larvæ.
Microgaster glomeratus.
After the caterpillar ceases from feeding, it crawls aside for the purpose of assuming the pupal state. But, before it can do so, the ichneumon larvæ, which have also ceased from feeding, burst their way through the sides of the caterpillar, and immediately begin to spin their cocoon. These are oval, very small, and covered with yellow silk. A group of these cocoons is shown at Fig. 3. The innumerable fibres of these cocoons hamper the caterpillars so much that, in most cases, it seldom is able to stir from the spot, but dies in the midst of its enemies. Groups of these yellow cocoons can be found in every wall or paling near cabbage gardens. In a few days, the larvæ have passed through their pupal stage, assuming the winged state, and emerge from the cocoons through little circular doors, as seen in Fig. 2.
Our second illustration represents another species, Microgaster alveolarius, together with its cocoons. As before, the insect is shown of its natural size at la, and magnified at 1. The preliminary life of this insect is exactly the same as that of the preceding; but, instead of making a number of independent and separate cocoons, the insects spin so closely together that they form an edifice very much resembling a bee-comb. Fig. 5 represents one of these cell-groups of the natural size, and the edge of another group is shown at Fig. 4. A longitudinal section, slightly enlarged, is given at 3, in order to show the hexagonal shape assumed by the aggregated cells; and Fig. 2 shows the little lids which open to give egress to the insect. All these figures are drawn from specimens in my collection.]
Microgaster alveolarius.
LONDON: PRINTED BY W. CLOWES AND SONS, STAMFORD STREET AND
CHARING CROSS.