Lemmings off themselves by way of jumping off of cliffs.
Rodents in fiction tend to have specialized roles. The mouse steals food and spreads disease while avoiding cats and other predators, the rat does pretty much the same thing, the beaver builds dams, the squirrel acts nutty, and the hamster and guinea pig act as adorable house pets. One rodent, the lemming, has a very special role: killing themselves. While it is true that real life lemmings jump off cliffs, it's done for the purpose of migration. It is not the mass suicide that the media claims it to be. That doesn't stop writers from milking the urban legend for all its worth.
Film - Live Action