Creature unable to multiply? (5)

I believe the answer is:

adder

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'creature' is the definition.
(I have seen 'venomous creature' mean 'adder' so perhaps 'creature' could also mean 'adder')

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for adder that I've seen before include "Dread (anag)" , "British snake; summer" , "exhibit in the reptile house" , "1 of 21 [SNAKES]" , "Type of snake" .)

I've seen this clue in the Evening Standard.

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