Pet parasite (4)
I believe the answer is:
flea
'pet parasite' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for flea that I've seen before include "Bloodsucking parasite" , "high-jumper" , "Bug" , "In your ear, this insect is a rebuke" , "Jumping, biting insect" .)