INSECTS AND MANKIND 419 



practice of agriculture and gardening, by crowding together 

 on a comparatively small area of land enormous numbers of 

 plants of the same kind, cannot but lead to rapid increase 

 in the numbers of those insects of the district which can 

 feed on the cultivated plants (see pp. 111-112). Thus 

 cultivation tends to incite various insects to become pests, 

 and then the cultivator finds it needful to take measures 

 for the slaughter of the pests on a large scale. Similarly 

 the shepherd and the cattle- owner collect in a restricted 

 area flocks and herds of animals of the same kind, whose 

 large numbers and ready accessibility must tend to abnormal 

 multiplication of parasites of all groups. It is right that 

 men, annoyed by insect pests, should remember to how 

 great an extent the troubles that beset them are the direct 

 consequence of their own actions. 



As an example of an insect which in recent years has 

 become a factor of great importance in human industry on 

 several continents we may take the Mexican Cotton Boll- 

 weevil {Anthonomus grandis). This small, long-snouted 

 beetle (Fig. 86), never more than4mm. {\ inch) long, and often 

 much less, is a native of Mexico. In 1 892 it crossed the border 

 of the United States, appearing in the far south-western 

 corner of Texas, along the Gulf coast. Thence its advance 

 has gone on, sometimes at the rate of fifty miles a year, 

 and it has now spread into Louisiana, Tennessee, Arkansas, 

 Alabama, Georgia, Florida, and the Carolinas, thus over- 

 running nearly the whole '' cotton belt " in the course of 

 some thirty-five years. The female beetles after hiberna- 

 tion bite small holes in the buds or the flowers and lay their 

 eggs therein, the grubs feeding in shelter or concealment 

 and pupating within the blossom or the capsule (*' boll "). 

 The beetles, after emerging from the pupal coat, continue 

 to feed for weeks or months, so that the damage done to the 

 crop in all stages of the insect's life-cycle is very heavy, 

 though it has been computed that in the northern parts of 

 its range, only about 2 per cent, of the beetles survive the 

 winter. The annual money loss due to the ravages of this 

 insect has been estimated at £50,000,000, and the President 



