50 THE MEXICAN COTTON-BOLL WEEVIL. 



Table XV. — Duration of life of boll weevils according to sex. 



Table XV in some respects bears out other findings as to the 

 superior hardihood of the female sex. It will be noticed that the 

 female's superior vitality is shown in all the cases where the food 

 supply is abnormal. Nevertheless, it is noticeable that in the case 

 of weevils fed on squares and bolls the males had the greater longevity. 



CANNIBALISM. 



It is hardly proper to speak of cannibalism as a food habit of the 

 boll weevil, but the facts observed may well be recorded here. Under 

 the impulse of extreme hunger weevils have several times showed a 

 slight cannibalistic tendency. 



Seven beetles were confined in a pill box without food. On the 

 third day six only were alive. Of the seventh only the hardest 

 chitinized parts (head, proboscis, pronotum, legs, and elytra) 

 remained, the softer parts having been eaten by the survivors. 



In another box containing 12 adults the leaf supplied for food was 

 insufficient, and on the fourth day eight were dead, four were partly 

 eaten, and others had lost one or more legs each. 



In another case a few young adults and a number of squares con- 

 taining pupse were placed in a box together with a few fresh squares 

 to serve as food for the adults. When the box was opened after a 

 number of days one adult was found having its elytra eaten through 

 and most of its abdomen devoured. In spite of this mutilation the 

 victim was still alive and kicking slowly. The squares were still 

 fresh and fit for food, so that this is really the clearest case of canni- 

 balism observed. 



Frequently more than one larva hatches in a square, and when 

 this is the case a struggle between them is almost certain to take 

 place before they become full grown. Many cases have been 

 observed in which squares contained one living and one or more 

 smaller dead larvae, while in a few cases the actual death struggle 

 was observed. 



i From Bulletin 51, Bureau of Entomology, p. 48. 



