In one of his lectures at Cornell in 1951 V. Nabokov remarked to his students that "the caterpillar is a he , the pupa is it and the butterfly is she."
(Cf. http://factsanddetails.com/world/cat52/sub333/item1594.html)

An earlier comment, voiced by Hermann in "Despair" plays with another threesome: "The weighty German word for “money” (money in German being gold, in French, silver, in Russian, copper) was mouthed by him…"

I ignore how many similar approximations can be spotted in Nabokov’s writings (I only found these two), or if they should be placed side by side as deliberate indications of fairy-tale “threes.”  
Even when they are evaluated independently from this hypothesis, they retain their humoristic mood. Hermann’s observation is not discrepant from a madman ratiocination  but VN’s sentence about the “gender” of lepidoptera expressed during class is rather surprising.

Thoughts?