Insect on leaf, back to front (4)

I believe the answer is:

flea

I'm a little stuck... Click here to teach me more about this clue!

'insect' is the definition.
(I know that flea is a type of insect)

'leaf back to front' is the wordplay.
'leaf' anagrams to 'FLEA'.
But, I'm unsure how this is indicated.

'on' acts as a link.

Can you help me to learn more?

(Other definitions for flea that I've seen before include "Blood-sucking parasites" , "Wingless, jumping insect" , "Small jumper in small circus" , "high-jumper" , "Bug" .)

I've seen this clue in The Guardian.

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