Pests having a bit of a race on the motorway (4)
I believe the answer is:
mice
'pests' is the definition.
Although both the answer and definition are plural nouns, I can't understand how they can define each other.
'a bit of a race on the motorway' is the wordplay.
'a bit of a race' becomes 'ice' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' means one lot of letters go next to another.
'the motorway' becomes 'M' (as in motorway names - Mi, M4 etc).
'ice' put after 'm' is 'MICE'.
'having' is the link.
Can you help me to learn more?
(Other definitions for mice that I've seen before include "Computer controls" , "Tiny rodents" , "people lacking character" , "''Of ... and Men'' (John Steinbeck)" , "Squeaking rodents" .)