Particularly throughout the first half of the novel, Grenouille is described as a “tick,” in that he is ugly, lies in wait without being entirely aware of what he's waiting for, and "drops" when he scents blood (or in Grenouille's case, perfume). The tick, then, represents how Grenouille is seen by the outside world (compared to how Grenouille sees himself; compare the tick to the Grenouille that exists in his inner palace). In a very literal sense, the comparison of Grenouille to a tick alludes to his vampire-like tendencies. Like a tick or a vampire, Grenouille metaphorically sucks his victims dry of their lifeblood in the form of both their scent and their lives, without any conception of morality, right, or wrong. Like a tick, robbing victims of their blood or scent is just what he does, and seemingly what he must do to survive.
The Tick Quotes in Perfume
The tick had scented blood. It had been dormant for years, encapsulated, and had waited. Now it let itself drop, for better or for worse, entirely without hope. And that was why he was so certain.