The Army of Lice spreads throughout most of the school in the Arthur episode "The Lousy Week". They are voiced by Billy West.
The Army of Lice first appeared on Muffy's head (which made Muffy make a sound very similar to Arnold's "Eaaghh eaaghh" from Total Recall) and quickly made their plans to spread throughout the entire school. Although Muffy was ordered home after the Nurse confirmed she had them, the Lice continued to spread as Francine put on Muffy's hat which she dropped on the floor, so they spread to her hair as well. They continued to spread as other students fondled with Muffy's hat before being told by the Nurse not to wear anybody else's clothes due to the infestation, and so the Army of Lice spread rapidly and even began appearing the hair of the teachers.
Soon the Army of Lice had spread so far and wide that the kids' parents were forced to take measures at home to keep them from getting beyond the school. The kids had to be checked everyday to see if the infestation was still ongoing, and those with longer hair like Francine and Muffy even cut their hair short to stop them. The only one unaffected by the Lice was Buster, who's lack of personal hygiene made his hair too disgusting for the lice to reside in.
Though the Army of Lice had spread far, eventually the kids were able to beat them back and eventually only the General was still alive. In a last bid to rebuild his Army of Lice, he tried to jump to Buster from George's head, only to fall to the floor of the school where he was stepped on by the kids.
General Louse is the leader of the army that spread throughout the school. Apparently a veteran of many previous battles, the general is a strategic leader. He sends his troops to spread nits as soon as they make contact on a new head. He does show a sense of control, as he found Buster to be uninhabitable, so he didn't even try to get him. After two long weeks, the general was the last survivor of his squad. Making a final gambit to escape to Buster and rebuild his army, his jump fell short and he was stepped on.
The Lieutenant Louse is the second-in-command of the army.
Although his light-gray mustache would imply age, and with it experience, the lieutenant is actually more cowardly than the rest of the army. He panicked at the sight of a hair clip, mistaking it for a comb.
It is uncertain exactly what role he played in the army, as he was not a strategic commander like General Louse, and did not do heavy lifting with the rest of the troops. His fear of combs would imply he be eventually defeated by one, but he was instead taken off Mr. Ratburn's head by the nurse's tongue depressor.