[citation needed] In autumn, they must time their movement back to sheltered higher ground carefully, leaving after alpine snow cover is available for their burrows and nests, and before the lowlands are made uninhabitable by frost and ice.

When the seasons are particularly good (short winters without unexpected thaws or freezes, and long summers), the Norway lemming population can increase exponentially; they reach sexual maturity less than a month after birth, and breed year-round if conditions are right, producing a litter of six to eight young every three to four weeks.

[citation needed] Being solitary creatures by nature, the stronger lemmings drive the weaker and younger ones off long before a food shortage occurs.

Where geographical features constrain their movements and channel them into a relatively narrow corridor, large numbers can build up, leading to social friction, distress, and eventually a mass panic can follow, where they flee in all directions.

According to genetic research,[5] the Norwegian lemming survived the Pleistocene glaciation in western Europe, inhabiting various refugia which were not covered by ice.

[2] Despite their diminutive size, when confronted at close quarters by a potential predator, mainland Norway lemmings characteristically become highly aggressive.

It is thought that prior to the Eemian Interglacial, L. lemmus was distributed widely throughout the Arctic Shelf from Western Europe east to Novaya Zemlya, and sea level rise during the Eemian left the species in its present-day disjunct distribution, with populations only on Fennoscandia and Novaya Zemlya.