Zoological Museum > New Danish spider

The large, handsome Trochosa robusta has until recently been living unobserved, despite its considerable size, on the island of Bornholm. The body itself is about 2cm across, while the legs extend to a diameter of 5-6cm, which is big by Danish standards. If you haven't yet stumbled over this species it is probably because it prefers to live on  chalk sea-cliffs, where it hides during the day-time in cracks and fissures. It only emerges at night to hunt insects on the vertical cliff faces.

A new spider species in Denmark, Trochosa robusta. Foto: Nikolaj Scharff

Whether the species has recently arrived on Bornholm or has been here the whole time but without being discovered, we don't know, but it was only when a comprehensive survey of Danish spiders was undertaken from 1997-2006 that its presence in the country was recorded. Denmark is presumed to be the northerly limit of Trochosa robusta's range, as it is common in Germany and Poland but is not present in other parts of Scandinavia.

A Danish 'tarantula'

Denmark also has its own member of the mygalomorph spiders (to which the hairy tarantulas belong), and that's not even something new! The purse-web spider Atypus affinis was previously known from Denmark, but as it hadn't been seen for 60 years despite persistent searching, it was considered  extinct. In 1994, it was rediscovered in Jutland, however.

Rediscovered in Denmark, the purse-web spider Atypus affinis. Foto: Nikolaj Scharff.

This unusual spider is also one you're not likely to stumble upon, but if you did it would not be so very frightening. Certainly its size is not insignificant, with a body up to 1.5cm across, but it has relatively short legs, and so it doesn't look very tarantula-like. However if you look closely you can see that, unlike most northern European spiders, it has large black ”jaws”, with downward-pointing poison fangs. This identifies it as a mygalomorph, the group to which the bird-eating spiders belong and which are mostly found in the tropics. It's not unusual that it's not especially big – most of the so-called bird-eating spiders are in fact rather small.

The purse-web spider spends its whole life hidden in a silken tube it weaves underground, apart from when the sexually mature males go out in search of a mate. And that's how the species was rediscovered in Denmark!  The spider's lair is about 30-50cm long, closed at both ends, and the last 5-10cm emerges overground, camouflaged by leaves and debris, where it functions as a trap. The spider waits inside at night-time until an insect or wood louse lands onto or crawls over the trap. The spider then stabs its long fangs through the silk tube and seizes its prey, which is killed and dragged inside for consumption.

The Danish spider recording scheme has shown that the purse-web spider is present in a number of locations in Jylland, on Sjælland, on the islands around Fyn and on Bornholm, and that the species seems to be doing well.

New species from warmer climes

The Danish spider recording scheme also revealed new spider species for Denmark. One of them is Zodarion rubidum, which originated in the Mediterranean, where there are a number of members of the ant-eating spider genus Zodarion. During the last few decades it has gradually spread northwards and is now resident in Denmark, which is presumed to be the current northerly limit of its distribution.

A beautiful immigrant from warmer climes, Zodarion rubidum. Foto: Jørgen Lissner.

All records are from derelict railway areas so the species may have been spread by goods trains. It prefers warm, stony areas with little vegetation. Zodarium hunts at night and hides in small igloo-like retreats during the daytime. We don't know how long it has been in Denmark, but many individuals of both sexes were found in the survey, so it seems to be well established here. 

About the survey

The Danish spider recording scheme began in 1997 and was completed in 2006. The results increased the number of species on the Danish list to 526, no less than 86 of which had never been recorded in this country before. In the last year a further three new species have been added, and you can see the current complete list as it is updated on this webpage:
http://www.zmuc.dk/EntoWeb/arachnology/dkchecklist.htm.

The survey has been published as: Scharff, N. & O. Gudik-Sørensen: Katalog over Danmarks edderkopper (Araneae). Entomologiske Meddelelser no. 74, pages 3-71. It was supported by the Zoological Museum of Copenhagen and the Natural History Museum in Århus , but also by a huge effort on the part of voluntary groups without whom the project would not have been possible.