A "cootie" is an informal name for which parasite?

I'd never heard "cootie" used as a reference to lice. Growing up, I knew of cooties as imaginary critters that were carried by the opposite sex: one reason little boys and girls wouldn't want to play together.

A nit picker is a person whose job it was to remove lice eggs, called nits, from someone's hair. This tedious task was performed by grasping each individual egg that was attached to a strand of hair by the thumb and index finger and sliding it down the shaft...one nit at a time. That is why the word "nitpicky" describes a person who concentrates on small and unimportant details especially to try and find fault with something.

In To Kill a Mockingbird (the book) one crawls out of one of the Ewells’ hair, and the teacher freaks out. She called it a cootie I believe.

As a kid a cootie was the mark left on the foot from hookworm infestation, usually caught by walking barefoot in sheep or cattle pens. When I read the word in an American novel I couldn't figure out how the children got them on their heads. This explains it.

Laudy Miss Claudy, these days a nit comb and lyclear do the job