210 NATURE STUDY AND LIFE 



with moist earth, into which they may burrow when they 

 wish to transform, since they either burrow or make their 

 cocoons on the surface of the ground. The larvae are 

 especially interesting from the number of ichneumon flies 

 parasitic upon them, and by keeping some in the viva- 

 >rium, a school is almost certain to be afforded the spec- 

 tacle of a swarm of minute larvae suddenly boring their 

 way out and spinning their little cocoons all over the back 

 of their host. Do not say much about it beforehand, but 

 when the first signs appear, gather the class around and 

 let them wonder about it. They will learn a lesson never 

 to be forgotten. 



Plant Lice, or Aphids. These are among the commonest 

 and most annoying insects we have. They infest almost 

 every plant of the conservatory, garden, field, and forest 

 and often become extremely destructive. Their mode of 

 life consists in puncturing the plant and sucking its sap. 

 Tlfey may attack the roots, as does the corn plant louse, 

 Aphis maidis, or they may live on both the roots and 

 leaves, as does the grape phylloxera, Phylloxera vastatrix, 

 or they may occur on roots and bark, as does the woolly 

 apple louse, Schizoneura lanigera. The greater number 

 of species confine their injuries to the tender, growing 

 parts, leaves, buds, and young fruit, as, for example, 

 the green apple-tree aphid, A. mali, the peach-tree aphid, 

 Mysus persiccz, and the common aphids of the rose, elm, 

 carnation, and many other trees, shrubs, and plants. 



Many kinds of plant lice have a pair of minute tubes 

 on the back, through which a sweet fluid, honeydew, is 

 excreted. This often covers the leaves and even the pave- 

 ment under the trees. Injury to the trees is increased by 



