Norwegian Journal of Entomology - Norsk entomologisk forening

landed after flying. The general snow depth was
about 1 m. As seen from Table 1, Philodromus sp.
has been collected on snow from several localities
and years, and mainly in April.
Weather conditions
Weather data are not available from all samplings,
but the temperature was usually noted. Figure 2
illustrates the climatic conditions during sampling,
when weather data were recorded. If temperature
varied during sampling, the mean temperature is
given. Conditions when B. index was observed
on snow are in black and show that this spider
prefers temperatures above zero and calm, sunny
weather. When the climatic data for all species are
combined, the temperature range spans from –7
to 14 o C, with most observations around or above
zero, often between 0 and 5 o C. However, several
observations were also below zero. In most cases
there was no wind, but the sky could be cloudy
or clear.
DISCUSSION
Spiders on snow: An annual
phenomenon with many species
involved
The present material from several localities and
throughout several years shows that spider activity
on snow is an annual, geographically general
phenomenon. Spiders were found in all winter
months. A large number of species participate
in this activity, but most species are uncommon.
Two studies from Northern Finland support this
general picture. In a large material of more than
two thousand spiders collected on snow, Huhta &
Viramo (1979) documented activity throughout
the winter except for the coldest period in
February. As many as 102 species were recorded,
most of them in relatively low numbers but with
a few dominant species. A smaller collection by
Koponen (1989) revealed fourteen species of
which four were regarded as regularly active on
snow.
Huhta & Viramo (1979) suggested that almost
any spider species present in the community
Norw. J. Entomol. 53, 71-82, 22 May 2006
may be found on snow. Most of the species in
the present material were also recorded by Huhta
& Viramo (1979), except for the following six
species represented by few specimens: Anyphaena
accentuata, Diplocephalus latifrons, Mugiphantes
suffusus, Obscuriphantes obscurus, Walckenaeria
kochi, Pachygnatha degeeri, and the genera
Acantholycosa, Araniella, Linyphia, Oedothorax,
Thanatus, and Xerolycosa. A common feature
of the present and the two Finnish studies was
a strong dominance of Bolepthyphantes index on
snow towards the end of the winter, in April.
Although the snow spider fauna in Southern
Norway and Northern Finland have many species
in common, considerable differences exist
Figure 2. Climatic conditions when spiders
were sampled from the snow surface. One
“observation” means that a species was present
on one occasion at that condition, for instance
temperature, but without indicating number of
individuals. Data for the most abundant species,
Bolepthyphantes index, are shown in black. Cloud
conditions are indicated as clear sky, partly
cloudy or completely cloudy (black). There was
either no wind, a faint wind (+) or a strong wind
(++). Finally, the number of observations are
given for foggy weather or when it was snowing.
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