THE SAND-LOVING AMMOPHILA 235 



with its head towards the opening or exit, whether it be in a 

 glass vial or in the natural earthen nest. 



FIG. 49. The pupal cases of Sphex pictipennis. Natural size. 



We have the exact record of the duration of the pupal 

 period in three cases. The two summer larvae, which pu- 

 pated June 5 and July 21, emerged as adults on June 28 

 and August 9, after pupal periods of 23 and 19 days re- 

 spectively, while one which spun its cocoon a little later in 

 the season, September 10, remained dormant until the sur- 

 prisingly late date of September 24 of the following year, 

 or through a pupal period of one year and two weeks. 



The newly-spun cocoons (see fig. 49), like that of Ody- 

 nerus dor sale and 0. geminus, are at first beautifully milky 

 white; later they become brown, sometimes of a light shade, 

 and sometimes dark. However, when these larvae spin in 

 glass vials, their cocoons are not symmetrical as in their 

 native habitats, and, after the silken part is done, some thick 

 strings of black substance remain. This is probably the 

 excrement which normally is spread or thrown over the 

 silken cocoon to darken and reinforce it. 



Sometimes the larva seems very greedy in devouring the 

 last dried bits of its shrivelled caterpillar, but, although it 

 appears hungry, it seems discriminating in the choice of its 

 food. We have been unable to induce it to take other food, 

 although we have offered it a tempting variety Cecropia 



