Insect seen on stand - a cause of anxiety (7)
I believe the answer is:
bugbear
'a cause of anxiety' is the definition.
(I've seen this before)
'insect seen on stand' is the wordplay.
'insect' becomes 'bug' (bug is a kind of insect).
'seen on' means one lot of letters go next to another.
'stand' becomes 'bear' (both can mean to tolerate or endure).
'bug'+'bear'='BUGBEAR'
(Other definitions for bugbear that I've seen before include "Thing causing obsessive anxiety" , "Cause of obsessive fear" , "Bete noire" , "bogeyman" , "Nuisance" .)