14 Habit and Instinct. 



The silvery, straw-coloured insects emerge from their 

 chrysalis-cases just when the large, yellowish-white, bell- 

 shaped flowers of the yucca open, each for a single night. 

 From the anthers of one of these flowers the female moth 

 collects the golden pollen, and kneads the adhesive 

 material into a little pellet, which she holds beneath her 

 head by means of the greatly enlarged bristly palps. Thus 

 laden, she flies off and seeks another flower. Having found 

 one, she pierces with the sharp lancets of her ovipositor the 

 tissue of the pistil, lays her eggs among the ovules, and 

 then, darting to the top of the stigma, stuffs the fertilizing 

 pollen-pellet into its funnel-shaped opening. 



Now, the visits of the moth are necessary to the plant. 

 It has been experimentally proved that, in the absence 

 of the insects, no pollen can get to the stigma to fertilize 

 the ovules. And the fertilization of the ovules is necessary 

 to the larvae, which in four or five days are hatched from 

 the insect's eggs. It has been ascertained that they feed 

 exclusively on the developing ovules, and in the absence 

 of fertilization the ovules would not develop. Each grub 

 consumes some twenty ovules, and there may be three 

 or four such grubs. But the ovary contains some two 

 hundred ovules. Of these, therefore, say, a hundred are 

 sacrificed to the grubs of that moth, through whose instru- 

 mentality alone the remaining hundred can be fertilized 

 and come to maturity. 



These marvellously adaptive instinctive activities of the 

 Yucca moth are performed but once in her life, and that 

 without instruction, with no opportunities of learning 

 by imitation, and, apparently, without prevision of what 

 will be the outcome of her behaviour; for she has no 

 experience of the subsequent fate of the eggs she lays, and 

 cannot be credited with any knowledge of the effect of the 

 pollen upon the ovules. The activities also illustrate what 



