Answer:
Lepidopterist
Explanation:
A linguist is a foreign language specialist, a lepidopterist collects butterflies, a philatelist collects stamps and a zoologist studies animals.
Vladimir Nabokov was a world-class Lepidopterist.
He was especially interested in the short novel "Metamorphosis" of Kafka, because it involves transformation into an insect, thus linking to his passion for butterflies and transformations.