Norwegian Journal of Entomology - Norsk entomologisk forening

Spiders active on snow in Southern Norway
Sigmund Hågvar & Kjetil Aakra
Hågvar, S. & Aakra, K. 2006. Spiders active on snow in Southern Norway. Norw. J. Entomol. 53,
71-82.
In Norway, insects and springtails which are active on snow have been fairly well studied, but not
the spider fauna. A sample of 439 spiders collected on snow during many years and from several
localities in South Norway, contained 46 species, including 12 which were only identified to genus
level. Spiders occurred on snow during all winter months, mainly at temperatures around or above
0 o C, but even down to –7 o C. Most species belonged to Linyphiidae. Comparisons with Finnish
pitfall-trapping below snow and a Norwegian study on the spider fauna on spruce branches during
winter show that nearly all species colonise the snow surface from the subnivean air space, probably
climbing up along stems and bushes penetrating the snow. In late winter, the spider fauna on snow is
dominated by Bolepthyphantes index, which constructs nets in small depressions in the snow surface,
for instance footprints of animals, and catches winter active springtails. During very warm days in
April, subadults of Philodromus sp. can start wind dispersal by sending out “flying threads” from
trees and may land in large numbers on snow. From there they probably seek snow-free patches. As
a group, spiders evidently contain many cold-adapted species, and Finnish studies have showed that
almost any species may be encountered on snow. Long-term pitfall trapping near Bergen showed
that some spider species had their main activity during winter, indicating winter reproduction. For
most spiders, their occurrence on snow in mild weather may simply be a continuation of their normal
subnivean activity. There should be a large evolutionary potential for more spider species to adapt to
use the food resource represented by winter active insects and springtails on snow.
INTRODUCTION
Key-words: Spiders, Aranea, snow, winter activity
Certain invertebrates are known to be regularly
active on the snow surface in Fennoscandia.
Well-known examples are the wingless insects
Chionea spp. (Diptera, Limoniidae) and Boreus
spp. (Mecoptera) which both lay eggs during
winter (Hågvar 1971, 1976, 2001), swarming
winter gnats (Diptera, Trichoceridae) (Dahl
1965) and Collembola migrating on the snow
surface (Leinaas 1981, 1983, Hågvar 1995,
2000). Winter active spiders, however, have been
much less studied. In Fennoscandia, spiders are
often observed being active on the snow surface,
Norw. J. Entomol. 53, 71-82, 22 May 2006
Sigmund Hågvar, Department of Ecology and Natural Resource Management, Box 5003,
Norwegian University of Life Sciences, NO-1432 Ås, Norway. E-mail: sigmund.hagvar@umb.no
Kjetil Aakra, Midt-Troms Museum, Box 82, NO-9059 Storsteinnes, Norway.
E-mail: kjetil.aakra@midt-troms.museum.no
mainly at temperatures around and above 0 o C.
Huhta & Viramo (1979) recorded more than
hundred species on snow in Northern Finland.
However, the function of this activity is little
understood. Only one species, Bolepthyphantes
index (Thorell, 1856), is known to have the regular
habit of building nets on the snow surface. The
nets are constructed over small holes or cavities in
the snow, for instance over foot-prints of animals.
This occurs mainly during late winter and the net
is used for catching winter active Collembola as
well as for feeding and mating (Hågvar 1973).
The study of Huhta & Viramo (1979) indicated
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