FACTFILE: Rodent visitor from the north

The Norway (or Norwegian) Lemming (Lemmus lemmus ) is a rodent belonging to the subfamily Arvicolinae, which includes voles and muskrats. It is found extensively in Fennoscandia, from the mountain range running north-south through Northern Norway and round to the fells of the northernmost reaches of Finnish and Swedish Lapland.
     
Lemmings swarm, or change their habitat, in the spring and autumn. The autumn migration actually begins in the summer months and can last through to October.
      The size of the lemming population depends on how well the creatures come through the winter. Lemmings breed in the winter and spend their time in nests under the snow cover.
      When the seasons are favourable, the lemming population can increase phenomenally, and the competition for food - and available partners - drives the animal to search out new territory.
     
Professor Heikki Hentonen of the Finnish Forest Research Institute METLA regards the present migration as being on a "moderate" scale.
     
It certainly does not compete with the mass exodus of 1970. Then lemmings were a common sight even in the streets of Rovaniemi. There were also a lot of lemmings around at the end of the 1970s and in the early 80s.
     
The suicidal tendencies associated with the lemming are a myth, for which Walt Disney's 1958 nature documentary White Wilderness is much to blame. Population sizes do fluctuate wildly, but the animals do not deliberately throw themselves to their deaths off cliffs.
     
A bite from a lemming (the animals are quite aggressive and fearless when aroused) can carry the infectious disease tularemia or "rabbit fever", borne by the Francisella tularensis bacterium. The animal can also be a carrier of a virus akin to Nephropathia epidemica, known variously as Puumala virus, or "Mole fever" - myyräkuume in Finnish or "Vole fever" - sorkfeber in Swedish. If you are bitten by a lemming, it is wise to seek medical attention.
     
Adult Norway lemmings are around 13 - 15 cm in length, with a tail of 1-2 cm. They have stout bodies, thick fluffy fur, small ears, and long claws. Even a fully-grown lemming will not weigh much more than 80-100 grammes. Their diet is mainly, grass, shrubs, and especially moss, and they also eat insects in the summer.
      As the photograph indicates, lemmings have no qualms about swimming.
     
Helsingin Sanomat / First published in print 31.8.2007

More on this subject:
 Lovelorn lemmings on the move, but not overly friendly

Links:
  Nature in Finland: Legendary Lemmings (Virtual Finland)
  Tundra Animals: Norway Lemming
  Snopes.com White Wilderness
  Norway Lemming (Wikipedia)