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.
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?