I grew vexed about a little pest (6)

I believe the answer is:

earwig

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'i' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for earwig that I've seen before include "Small insect with aural toupee?" , "One little creature" , "Go in for eavesdropping" , "Small insect with pincers at end of its body" , "An insect, I wager (anag.)" .)

I've seen this clue in The Globe and Mail.

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