INSECTS AND BIRDS. 279 



begins to look more like a boll weevil. The beak ap- 

 pears and the small wings can be seen just commencing 

 to grow. The pupa does not feed, for it lies helpless 

 within the square for about a week. At the end of its 

 pupal existence it changes into a perfect, full-grown boll 

 weevil, still within the square. Next it eats a hole in the 

 side of its "square house," large enough to get through, 

 and comes out ready to destroy more squares and bolls. 



Effect of Temperature on Growth. Heat has a re- 

 markable effect upon the development of the young in- 

 sects. When the weather is warm the eggs hatches 

 more quickly, and the larva grows much faster than 

 in cool weather. Thus in July the complete develop- 

 ment of the weevil, from egg stage to. adult, may take 

 place in 12 or 13 days. Early in the summer, during 

 May and June, nearly a month is required for the de- 

 velopment of a generation. In October and Novem- 

 ber, when the weather is cooler, the young boll weevil 

 may not reach maturity until 35 or 40 days after the 

 egg is laid. 



Migration. Early in summer the boll weevils are 

 not usually abundant, for the rigors of winter destroy 

 many of them. As soon as the squares appear on the 

 young cotton plants eggs are laid, and in a few weeks 

 the first brood of weevils reach maturity. Generation 

 after generation of weevils follow, until by the first or 

 middle of August there are thousands of them in the 

 cotton field, and the plants can no longer produce 

 squares enough to supply their wants. At this time 

 the weevils become possessed with a desire to find new 

 fields of cotton where there is more food for them. 

 Accordingly many of them fly up into the air and go 

 in every direction. This migration takes place during 

 August and September. Many of the weevils succeed 

 in getting to localities where there were no weevils be- 

 fore, and in this way the infested territory is increased 

 40 to 50 miles northward and eastward each summer. 

 It should not be understoood that all the weevils leave 

 a cotton field or locality when the migration takes 



