152 THE AMERICAN BOTANIST 



The Yucca Moth. — The orchids have long- been famous 

 for the methods they have adopted to secure pollination by 

 insects. Probably no other flowers have been so greatly modi- 

 fied in form for this purpose, but so far as insect ingenuity, 

 itself, is concerned, the prize must go, not to the insects that visit 

 tropical orchid flowers, but to a rather inconspicuous denizen of 

 our own fields and woods, the yucca moth (Promiba yucca- 

 sella). This insect, by means of a stout ovipositor, lays her 

 eggs in the young seed capsule of the yucca plant at the time 

 the flowers are blooming and the larvae, when hatched, feed 

 on the developing yucca seeds. The Yucca, however, owing to 

 the location and shape of its stigma, is incapable of self pollina- 

 tion, or even of being pollinated by ordinary flower-L ving 

 insects, and would therefore set no seeds were it not for the 

 ministrations of the moth. During the yucca's blooming 

 season, this remarkable insect may be seen just at dusk running 

 rapidly up one stamen after another and scooping out the 

 pollen which she makes into a tiny ball and holds between her 

 head and the lower side of her thorax. Flying usually to 

 another flower with her lead, she first lays an egg' in the ovary 

 and then climbing up to the stigma deliberately pollinates the 

 flower by pushing the pollen down into the stigmatic cavity 

 with much vigor. The larvae remain in the seed capsules until 

 mature and then crawling out, burrow into the earth where they 

 make a silken cocoon in which they rest until the yuccas bloom 

 again. When the first yucca blossom opens, the moth soon 

 finds it and during the entire blooming season remains in the 

 blossoms, changing to new flowers as the old ones fade. So 

 closely do the moths resemble the thick stamens that they may 

 frequently be overlooked by those not in the secret. Where 

 the yucca grows wild, it is of course never without its 

 attendant moth, otherwise the family line would soon run out. 

 In cultivation it may frequently be absent, though wherever the 

 plant sets seeds without assistance from man, the moth is sure 

 to be present, and the round holes in the seed capsules, through 

 which the mature larvae escape, are further evidences of the 



