Thank you, Barrie and Bedja.I also personally asked these terms to the Nabokov biographer Andrea Pitzer and toRene Alladaye, the writer of the latest Pale Fire book. Mr. Alladaye also states thatvolant en arričre means "flying backwards". But curiously, the term also has the
meaning which was already given in the very same sentence: a heraldic insect. Pleasecheck the link given by Andrea Pitzer:
Would it be correct to say, then, that Nabokov only makes a repetition here:a heraldic butterfly is a winged insect; in other words, a volant en arričre...