BENEFICIAL INSECTS, PKEDACEOUS AND PARASITIC. 43 



where one of these pcarasites has emerged. For this reason 

 as a general rule dry, shrunken plant-lice shonld never he 

 destroyed. 



The Ohalcis-flies, which comprise another closely re- 

 lated famih', are exceedingly minnte insects, sometimes 

 not over one one-hundredth of an inch long. They are 

 generally of a metallic black color, and the nsnal veins of 

 the wings are almost entirely absent. Many of these flies 

 are parasitic npon plant-lice, while a large number of their 

 larva? live and mature in the eggs of other insects. 



Very similar to the Chalcis-flies in their habits of infest- 

 ing plant-lice and insect eggs are some even smaller insects 

 — in fact the smallest known, the largest being rarely over 

 one twenty-fifth and the smallest only six or seven one- 

 thousandths of an inch in length — with a correspondingly 

 tremendous and unpronounceable name, known to science 

 as the Proctotryjndce, 



But enough has been said to indicate the important j^art 

 which the immense hordes of these apparently insignificant 

 insects play in the economy of Nature, by often clearing 

 off a most dreaded insect pest in a few days almost as if 

 by miracle. 



