They were introduced in Operation: H.O.U.N.D., where Numbuh 5 is attacked by one that eats her homework on the way to school. She at first assumes it was a dog belonging to her academic rival, Valerie, but when she arrives at Valerie's house to investigate, she learns that the monster was Valerie herself who was eating all her homework in an attempt to secure her position as top student of their class.
After trying to kill Numbuh 5, Valerie was defeated by Numbuh 4, whose terrible homework is apparently poisonous to weredogs. After this, the kids' homeroom teacher, Mrs. Thompson, arrives on the scene and says that she will be giving Valerie detention, only for the audience to then learn that she too is a weredog.
This storyline continues in Operation: D.O.G.H.O.U.S.E, when Mrs. Thompson turns Numbuh 5 into a weredog because she was attacked from the previous episode, and forces her to collect homework for her in exchange for the cure. Numbuh 4 appears and tries to save her, but is overpowered. Fortunately, Numbuh 4's tendency to ask questions to Mrs. Thompson saves his life when he gets her to explain that the source of the curse is the amulet she is wearing, which contains the soul of the Queen Weredog. Numbuh 5, still a weredog, accidentally removes her amulet while trying to catch her, thus lifting the curse.