Insect doing backflips in rectangles (4)
I believe the answer is:
gnat
'insect' is the definition.
(gnat is a kind of insect)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for gnat that I've seen before include "Tiny thing" , "Small biter" , "insect's" , "mozzie" , "little irritation" .)