82 CEREAL AND FORAGE INSECTS. 



year. After that date pupation very rapidly became general over the 

 entire range country and continued until after September 20, at which 

 date a few larvae were still found to be feeding. 



Without doubt abundance or scarcity of food hastens or retards 

 the date of pupation, since this is a potent factor throughout the 

 whole life history of this species of Hemileuca. Near the foothills, 

 where showers were more or less frequent and grass abundant, pupa- 

 tion began twelve days earlier than on the dry mesa in the vicinity of 

 Springer, 30 miles distant, where rain fell but seldom during the sum- 

 mer of 1909, and the grass was correspondingly short. 



Although the time of pupation is a critical one in larval life, con- 

 ditions are so favorable in New Mexico during the summer season 

 that very few out of the millions that undergo the ordeal fail to pass 

 it successfully. The singularly dry air with its warm day tempera- 

 ture seems to afford exactly the conditions that are needed. 



LENGTH OF PUPAL STAGE. 



The duration of the pupal stage varies greatly, owing to causes 

 not wholly explained. Several individuals, taken and kept in con- 

 finement from the time the caterpillar was full fed, disclosed adults 

 within about five weeks after the pupa was formed. 



Others again, kept under very similar surroundings, remained as 

 pupa? for seven and eight weeks, even longer in a few instances. No 

 moths emerged in less than five weeks, and this period must be taken 

 as the minimum, with perhaps nine weeks as the maximum. 



THE MOTHS. 

 EMERGENCE. 



The great majority of the Hemileuca moths emerge from the pupae 

 early in the morning, as soon as the chill of night has gone. Upon 

 leaving the cocoon they make their way at once to the upper or outer 

 part of the plant in which they have passed the five weeks of pupal 

 life. Clinging to a stem or twig, they rock the body to and fro, if 

 there is no air stirring, and rapidly dry their limp wings. At first the 

 wings are thrown back from the body until they become firm and 

 normal, then they are roofed closely over the back in the position 

 shown in figure 42. This is the customary resting attitude of the 

 species. The secondaries are often advanced beyond the primaries 

 until the costal margin shows slightly. 



The freshly emerged moths remain perfectly quiet during the day 

 (Plate IV, fig. 1), except when, as occasionally happens, a sudden 

 gale from the foothills drives them to take shelter in the lee of their 

 plant, for they seem to have a great dislike for wind. 



If the moths are disturbed on this first day of adult life, the female 

 promptly voids the contents of her defensive sac (as described else- 



