Insect collector left pet spider to one, unexpectedly (13)

I believe the answer is:

lepidopterist

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'insect collector' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?

'left pet spider to one unexpectedly' is the wordplay.
'left' becomes 'l' (common abbreviation).
'one' becomes 'i' (Roman numeral).
'unexpectedly' indicates an anagram.
'pet'+'spider'+'to'+'i'='petspidertoi'
'petspidertoi' is an anagram of 'epidopterist'.
'l'+'epidopterist'='LEPIDOPTERIST'

Can you help me to learn more?

(Other definitions for lepidopterist that I've seen before include "one with commas to check?" , "Butterfly enthusiast" , "Butterfly expert" , "Student of moths and butterflies" , "One who studies butterflies and moths" .)

I've seen this clue in The Times.

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