Parasites making right marks (5)
I believe the answer is:
ticks
This clue might be a double definition.
'parasites' is the first definition.
(I've seen this before)
'marks' is the second definition.
(I know this)
'making right' acts as a link.
I am not very happy about this link. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for ticks that I've seen before include "covers" , "Marks correct" , "Marks of approval" , "They suck from warm-blooded animals" , "Signs of approval" .)