Lemmings have gotten a bum rap as being panicky rodents prone to throwing themselves from cliffs during their annual migration. But it turns out that the "documentary" that first promulgated this lie was more snuff fantasy than scientific fact. You don't normally expect that from a Disney production.
The year was 1958. The film was White Wilderness, a nature documentary highlighting life in the subarctic North directed by James Alga. Except there was very little actual documenting going on. The famous scene that first promoted the misconception that lemmings A) regularly migrate and B) commit mass suicide was in fact entirely staged.
First off, the film was made in Alberta, Canada. Lemmings aren't native to that region so the production crew instead imported a few dozen of the animals for the shoot. Second, the species of lemming that they lined up does not migrate. Some species of lemmings do migrate, sure, when their cyclical population growth presses some individuals to move to less crowded areas. But you'll never see a herd of migrating lemmings like you do in the film (no matter how adorable that would be).
As such, the crew actually had to employ a snow-covered turntable to make it appear that they were "migrating" when they were really just running in circles. After the crew had a sufficient number of these migratory shots, the animals were herded over to the bank of a nearby river and unceremoniously chucked into the water, where they drowned. Thus the myth of suicidal lemmings was born.
Cruel? Definitely. But this was 1950s Hollywood, where animal cruelty was tragically common. Studios had, for example, killed over 100 horses for a single scene in Ben Hur and stabbed a lion to death for Tarzan, so killing off a few dozen rodents for the amusement of theater-going audiences was seemingly no big deal.
It wasn't until 1982, when the Canadian Broadcasting Corporation's investigative journalism program The Fifth Estate ran an expose entitled Cruel Camera on Hollywood's sickening treatment of animals, that the story of the lemmings' demise reached the public. But, by that time, White Wilderness had already won an Academy Award for Best Documentary Feature—and the myth of the cliff-jumping lemmings was already set in stone. [Wiki - Way Back Machine - snopes]