In very small numbers, it can be a nuisance (6)
I believe the answer is:
weevil
'it can be a nuisance' is the definition.
The definition suggests a singular noun which matches the answer.
'in very small numbers' is the wordplay.
I cannot really see how this works, but
'very' could be 'v' (abbreviation) and 'v' is found in the answer.
'small' could be 'wee' (Scottish term for small) and 'wee' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for weevil that I've seen before include "Small kind of 15 down" , "Small beetle, crop pest" , "Small beetle, pest of crops" , "Insect that feeds on plant products" , "Small beetle that feeds on plants" .)