DEATH OF THE CATERPILLAR. 327 



parasites seems to have no effect on the caterpillar, who eats as 

 voraciously and grows as rapidly as if it were free fi'om its in- 

 ternal devourers. 



All, therefore, goes on apparently well, until the time when 

 the insect ought to make its change to the pupal state, being 

 full-fed, or at least as full-fed as it can be. But the larvce of 

 the Microgaster are full-fed too ; and, just before the caterpillar 

 changes into the pupa, they burst through it in all directions 

 and leave it to die. Generally, it dies so soon that its shrivelled 

 body remains in the midst of its enemies, and it seldom has 

 sufficient strength to move more than a few inches away from 

 them. The Ichneumon larvse immediately begin to spin for 

 themselves little yellow cocoons of silk, very much resembling 

 that of a silkworm, and clustered closely" together. I have 

 noticed that those which come from one caterpillar generally 

 congregate into two totally distinct clusters, those which occu- 

 pied the different sides of the caterpillar remaining neighbours 

 as before. The specific name of glumeratus, or clustered, 

 refers to this habit. 



Almost any number of these cocoon-clusters may be obtained 

 from the walls, posts, or palings that adjoin kitchen-gardens ; 

 and the tree-trunks of the garden are equally prolific in them. 

 If a cocoon be cut open with a very fine pair of scissors, the 

 pupa may be seen lying in its silken cell, and, with a little care, 

 the whole progress of the insect can be watched, from the larva 

 to the pupa. I have dissected great numbers of cabbage cater- 

 pillars for the sake of observing the curious relationship between 

 the caterpillar and the Ichneumon, and the development of 

 the latter insect. 



There is a closely allied species, named Microgaster alvearius, 

 which in many things resembles the preceding species, but which 

 has a different method of arranging its cocoons. Those of the 

 preceding insect are arranged quite at random, or indeed can 

 scarcely be said to be arranged at all, the larvse spinning their 

 cocoons without any reference as to the position in which they 

 might happen to be at the time. But, the present insects 

 when they are about to change into the pupal state, arrange 

 their cocoons side by side with the greatest regularity, as seen 

 at Fig. d on Woodcut XXXII. Masses of these pretty cocoonff 



