498 HOMES WITHOUT HANDS. 



and shape of a scarlet-runner bean, split longitudinally, and are 

 bound so tightly together that their shape can barely be distin- 

 guished through the enveloping threads. 



As is the case with the cells of the Burnet ichneumon, each cell 

 is furnished with a little circular door, which exactly resembles in 

 shape and dimensions the circular pieces of paper that are punch- 

 ed out of the edges of postage-stamps. On the average, about 

 sixty or seventy ichneumon flies are produced from a single cab- 

 bage caterpillar. 



The groups of yellow cells are very plentiful toward the mid- 

 dle of summer and the beginning of autumn, and may be found 

 on walls, palings, the trunks of trees, in outhouses, and, in fact, in 

 every place which affords shelter to the caterpillar. Nothing is 

 easier than to procure the insects from the cocoons, as the yellow 

 mass needs only to be put into a box, with a piece of gauze tied 

 over it by way of a cover. Nearly every cocoon will produce its 

 ichneumon, and as the little creatures are not strong-jawed enough 

 to bite through the gauze, they can all be secured. 



There are many species of Microgaster ; but those which have 

 been mentioned are the most important, and make the most inter- 

 esting habitations. 



The large oval cocoon was brought from New South Wales, 

 and is evidently the produce of some lepidopterous insect, proba- 

 bly a moth allied to the silkworm. Upon the larva which con- 

 structed the cocoon an ichneumon has laid her eggs, and the con- 

 sequence has been that the caterpillar has been unable to change 

 into the pupal condition, but has succumbed to the parasites 

 which infested it. These insects are not of minute dimensions, 

 like the Microgaster, but are tolerably large, and, in consequence, 

 can be but few in number. The cells are very irregular in shape, 

 and are not rounded like those of many Ichneumonidas, but have 

 angular edges. 



In this, and in one or two other examples which are shown in 

 the illustration, the reader will note a peculiarity in the develop- 

 ment of the parasite. The Microgaster larvas emerge from the 

 caterpillar just before it undergoes its change into the pupal con- 

 dition, and effectually prevent that change by killing the creature 

 in which they had been nurtured. But, in many instances, the 

 ichneumon larva delays its escape until the caterpillar has com- 

 pleted its cocoon, and in some cases waits until the change into 



