Insects making right marks (5)

I believe the answer is:

ticks

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'insects' is the definition.
(I have seen 'Parasitic insects ' mean 'ticks' so perhaps 'insects' could also mean 'ticks')

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for ticks that I've seen before include "Marks right" , "Makes noise like old clock" , "Parasitic mites" , "Bloodsuckers; seconds" , "Small arachnids" .)

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