190 APHIDES, OR PLANT-LICE. COCCIDyE. 



fertile eggs ; and from these are reared the winged males and 

 females, which are seen later in the season. Their rapidity of 

 production is enormous ; nine generations having been produced 

 within three months, and each generation averaging 100 indivi- 

 duals. Hence it may be calculated that, from a single Aphis, 

 10,000 million millions may be generated in that short period. 

 It is not surprising, then, that an immense amount of damage 

 should be done by them, notwithstanding their very small size. 

 Many of the blights so injurious to the gardener and the agricul- 

 turist, consist really of Aphides ; although from the minuteness 

 of the insects themselves, they frequently escape observation. 

 The Aphis Roscs^ or Rose Louse, is one of those best known to 

 the gardener ; whilst the one most destruc- 

 tive to the property of the cultivator on a 

 larger scale is the Aphis Humuli, or Hop 

 Fly. Of the extent of its influence on the 

 **' production of that vegetable, some idea 

 may be formed from the fact, that the duty paid to the English 

 government on its growth, has varied from 468,OOOJ, to 15,400/. 

 in different years, almost entirely from the absence of this insect 

 in the former case, and its presence in the latter ; and the differ- 

 ence in the actual value of the crop is, of course, far greater. 



720. Section III. MONOMERA. The third section contains 

 but one family, that of COCCID.E, sometimes called Scale Insects. 

 These, although ordinarily of very small size, are amongst the 

 most injurious to vegetation of the whole tribe. Like the last, 

 they are remarkable for their powers of propagation ; and when 

 they once gain possession of a plant or young tree, its death is 

 almost certain, the minute size of the larvae rendering it almost 

 impossible to exterminate them. They furnish, however, some 

 very important products. The bodies of many species are deeply 

 coloured through their whole substance, and yield dyes of great 

 value ; the richness of which seems to depend upon the nature 

 of the plant on which they feed. The Coccus of the ancients 

 was a native of the Levant; but that which furnishes the 

 Cochineal so highly valued at the present time, was originally 

 confined to Mexico, where it feeds on the plants of the Cactus 



