Nature in Finland
The Norway lemming’s range is limited
to the arctic fells and tundra of northern Fennoscandia –
where it is found in north-westernmost Russia and northern parts
of Finland and Sweden, as well as in Norway.
Photo: Nature Photo Agency/Heikki
The numbers of Norway lemming in northernmost Finland
vary greatly from year to year, but during good lemming
years these small animals seem to pop up everywhere, especially
on migration between their winter and summer feeding grounds.
But this very limited global distribution
is not the Norway lemming’s only peculiarity, since this
small rodent is also notorious for the extreme fluctuations
in its numbers. Some years they seem to be everywhere, but during
other years they are only conspicuous by their absence.
Lemming populations, like those of
other northern rodents, typically exhibit pronounced cyclical variations
over periods of 3 –5 years, with numbers in peak years dozens of times
higher than during population slumps. The heights of these peaks also
vary, with Norway lemming populations evidently having particularly high
peaks every 30 years or so.
During these special lemming years,
populations are so dense that hikers on the fells of northern Lapland
can hardly move without sending the creatures scurrying off in every
direction. Some lemmings also become so fearless that they will boldly
stand their ground.
Lemming years have fired people’s
imagination since the middle ages. Some believed that lemmings
fell from the sky like rain, while others even suggested that
the animals were searching for their former home, the lost continent
of Atlantis. Priests even registered mass occurrences of lemmings
in church diaries, as they were also thought to be an omen of
Photo: Reijo Juurinen
Stoats and weasels commonly prey on Norway lemmings and
other rodents in northern Finland. This stoat is in its
A still more persistent piece of
folk wisdom claimed that hordes of lemmings would suicidally rush off
cliffs, fall into the sea and drown. Many people may even remember
witnessing this phenomenon in an old American TV "nature documentary";
but this was in fact an elaborately staged stunt, involving captive
lemmings released en masse, and deliberately driven towards some
Two more scientific explanations
have more recently been put forward to explain the phenomenon of lemming
The first and more widely accepted
theory concerns the predators that feed on lemmings – particularly
weasels and stoats. Lemming populations can increase during periods when
there are relatively few predators; but predator populations will then
increase, and consume more lemmings, soon causing a downturn in their
numbers. With their prey in short supply, the predators will
subsequently themselves decline, until the whole cycle can begin again.
The other theory holds that during lemming
population peaks mosses can produce and accumulate toxic or
foul-tasting chemicals to protect themselves from the voraciously
grazing rodents. This will reduce the available food supply,
and consequently lemming numbers, until the mosses no longer
need to produce the deterrent chemicals. The lemmings can then
start to feed on the mosses again, and proliferate.
Published November 2002