THE SOIL FAUNA: ANTHROPODS - The Soil - page 81

web, it is stabbed from below by the enormous vertical fangs of Atypus which then
cuts a hole in the tube and drags the victim inside. Several tropical relatives of this
mygalomorph spider build trap-doors across their burrows into which unsuspecting
prey can be precipitated.
The spiders which jump to catch their prey all belong to the Salticidae. They are
diurnal predators with keen eyesight. Most species are active climbers on tree trunks,
fences and walls, and are therefore outside our scope. However, a few are common in
woodland and fen litter or on stony ground. The crab spiders, Thomisidae, represent
the 'ambush guild'. They are characterized by the lateral extension of their legs and
their ability to scuttle sideways as well as forwards and backwards. Species of Xysti-
cus and Oxyptila are often found lurking among fallen leaves, waiting to pounce on
any small insect that comes within their reach.
The wandering or cursorial spiders belong chiefly to four families, but a few
from other families have abandoned the web-building habit; Pachygnatha , for ex-
ample, is a representative of the familiar orb-web spiders which has adopted a free-
ranging life style. Many are nocturnal hunters that shelter by day in silk-lined cells
under logs or stones. These range from the tiny Oonops pulcher , whose name means
beautiful egg-eyes, and which is only 1.5-2.0mm long, to the fearsome Dysdera and
Drassodes which may reach 15mm or more in length. Dysdera is unusual in its pen-
chant for woodlice; it is able to pierce the heavy armour of Porcellio and Oniscus as
well as that of the more generally palatable Philoscia ( Plate 8 ) .
The largest group of hunting spiders are the wolf spiders, Lycosidae. The females
are often noticed in summer as they scramble over rough ground and through ve-
getation with a large pale egg sac held securely in their spinnerets at the end of the
abdomen. Without this, the dull grey or brown colour of their bodies renders them
very inconspicuous on bare ground or on a woodland floor. The family includes thir-
teen species of Pardosa , all about 5 or 6mm in length and adapted for sprinting to
catch their prey. This genus provides a good example of the way in which morpho-
logically similar animals 'share out' the environment in a way that reduces compet-
ition between them through a combination of geographical and habitat preferences.
Some species are restricted, presumably by climatic features, to northern or southern
counties in Britain, while a more finely-tuned discrimination is achieved by staking a
claim to woodland, mountain, fen or coast, and the selection, within these, of damp
versus well-drained soils or exposed versus sheltered sites. “Every species” says Paul
Collinvaux “has its niche, its place in the grand scheme of things……Wolf spidering
is a complex job, not something to be undertaken by an amateur”.
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