Western snake that stings rather than bites (4)

I believe the answer is:

wasp

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'western snake that stings rather than bites' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'western snake' is the wordplay.
'western' becomes 'w'.
'snake' becomes 'asp' (asp is a kind of snake).
'w'+'asp'='WASP'

Can you help me to learn more?

(Other definitions for wasp that I've seen before include "Swap for a stinging insect" , "Buzzer" , "White Anglo-Saxon Protestant" , "Striped insect" , "Insect often irritating in summer" .)

I've seen this clue in the Evening Standard.

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