They appear in the episode "A Thing About Rats". The Mousers were created by scientist Baxter Stockman to rid the town of its rat problem. The Mousers attacked Splinter, but he held them off until the turtles came to his rescue and destroyed the remaining ones. Shredder angrily ordered Stockman to program them to also attack turtles. The Mousers attacked Splinter and April at April's apartment, and again were held off until the turtles arrived to destroy the remaining ones. However, by this time, the Mousers' constant chomping had weakened the apartment building, and it collapsed, although everyone inside escaped in time.