Insects on a vegetable, not so short (7)
I believe the answer is:
beetles
'insects' is the definition.
(beetle is a kind of insect)
'on a vegetable not so short' is the wordplay.
'on' is a charade indicator (letters next to each other).
'a vegetable' becomes 'beet' (beet is a kind of vegetable).
'not so' becomes 'less' (eg 'not so big' means 'less big').
'short' means to remove the last letter.
'less' with its last letter removed is 'les'.
'beet' next to 'les' is 'BEETLES'.
(Other definitions for beetles that I've seen before include "Four-winged insects" , "Lets bee turn to insects" , "Bet eels could turn into insects" .)