Some bugs are small and affectionate (5)
I believe the answer is:
swarm
'some bugs are' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'small and affectionate' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'and' is a charade indicator (letters next to each other).
'affectionate' becomes 'warm' (synonyms).
's'+'warm'='SWARM'
Can you help me to learn more?
(Other definitions for swarm that I've seen before include "Mass of flying insects" , "Large cloud (of insects)" , "Climb; cluster of bees" , "many insects" , "Host" .)