Mosquito
The type of insect that ruins your writing is the mosquito. You're trying to write, when you hear that horrible high-pitched mosquito noise in your ear. You jerk your head and swat and it's gone. But when you look down, there's lines all over what you were writing.
None
か
None
That mosquito noise sounds like it's driving a tiny car (か) in your ear. How are you supposed to write with a bug driving around going bzzz bzzz like a revving car?