128 HOMOPTERA. 



which their legions are unremittingly attacked, we are almost led to wonder 

 how any of them escape from such hosts of hungry and relentless foes. 



Let us not imagine, however, that these insects have been created in such 

 numbers merely for the purpose of destroying vegetation and of affording food 

 to voracious persecutors. Man, as we shall soon perceive, has by no means 

 been forgotten in their distribution. 



The Coccidse, so called from the valuable Grecian dye, R-O/CKO?, more than 

 counterbalance, by the richness of their productions, all the devastation caused 

 by the Aphides we have been describing, and various European and Asiatic 

 species are sources of considerable wealth to the countries where they are 

 found ; but the discovery of 



The Cochineal Insect (Coccus Cacti], which lives in immense numbers on the 

 Cactus Cochinilifer, from the brilliancy of the colour it affords (cochineal), has thrown 

 the dyes derived from other species into the shade, and has proved one of the most 

 productive sources of wealth to the countries where it is cultivated. Another important 

 species, the Coccus lacca, furnishes the valuable Indian product called lac, an article 

 of so much importance in the manufacture of varnishes, sealing-wax, &c. Another 



Ufper surface. Under surface. 



FIG. 131.* COCHINEAL INSECT (Magnified). 



species of Coccus is found upon the Tamarix mannifera, a large tree which grows in 

 Syria. The female insects, puncturing the young shoots, cause them to discharge a 

 vast quantity of a peculiar secretion (manna), which quickly hardens, and drops from 

 the tree, where it is collected by the natives. Other species produce in abundance a 

 substance almost identical with wax. The Chinese collect it at the approach of autumn 

 by scraping the boughs on which it is found. It is then melted and strained into cold 

 water, when it hardens, and is made into cakes exactly resembling white wax, and is 

 used for similar purposes. Various other important results of their industry might be 

 enumerated ; but we have said enough to show that these despised vegetable parasites 

 are by no means unprofitable members of the animal creation. 



Equally well known, and unfortunately almost as abundant as 

 the Aphides, are 



The Blight Insects (Psylla\ the pests of our orchards and the destruc- 

 tive causes of what is called the " blight " upon our fruit-trees. It would seem, 

 indeed, that every tree and shrub supports a special race of these creatures, 

 which are distinguished by entomologists by the names of the plants upon 

 which they are found. In the preparatory stages of their growth these insects 

 are generally covered with a white cottony substance, matted together with a 

 sweet and gummy secretion. 



