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European Society of Arachnology

European Spider of the Year 2007

The giant riverbank wolf spider - Arctosa cinerea (Fabricius, 1777)

European spider of the year 2007

Martin Kreuels, Jason Dunlop & Matjaz Kuntner

The giant riverbank, or sand wolf spider (Arctosa cinerea) is one of Europe's largest wolf spiders with a body length in males of 12–14 mm and in females 14–17 mm. Its highly contrasting light and dark (grey-brown or yellow-grey) markings make these ground-living animals almost impossible to detect when they remain still on a sand or gravel substrate (Bellmann 1997).

The species originally inhabits natural, dynamic gravel or sandy river and lake banks. It also occurs secondarily in sand and gravel quarries. On unregulated lakes and rivers this wolf spider resides on gravel and sandy banks near the water's edge in areas free of vegetation due to regular flooding. Regulation of lakes and river flow in the past decades has caused the extinction of this species in many parts of Europe.

The spiders are active between March and November, when they inhabit silken tube retreats, which they only leave to forage. Their silk tubes are buried in the sandy substrate and typically lie under large stones or flotsam such as pieces of wood. The position of the retreats is oriented towards the water's edge, where the animals can be found in a strip about 0.5 to 1.5 metres from the water. Their prey includes terrestrial beetles, fly larvae, grasshoppers and other spiders. From June to August the females carry and guard their egg cocoons. These hatch from August to October, the spiderlings over-winter and complete their development in the late summer of the following year. They then over-winter a second time after which, they mate and produce their offspring. Due to overlapping generations, adult spiders can be found all year round. During over-wintering the animals prepare another retreat, about 10 to 15 metres from the water's edge, sufficiently far away to avoid the danger of flooding. If flooding occurs in the summer the spiders simply seal the opening of their retreat and can survive in the resulting pocket of air. The distribution of the giant riverbank wolf spider ranges from the Mediterranean through Central Europe into Scandinavia and to the east as far as Siberia.

Further information about the Spider of the Year, including a poster about all previous selections and their distribution maps, can be found on the website of the Arachnologische Gesellschaft: www.arages.de/sdj/sdj_07.php

Supporting societies:

Thanks

As always, we would like to thank Aloysius Staudt for preparing the distribution map, and for updating these records during the year, and Dr. Heiko Bellmann for making his images available.