SOIL ARTHROPOD SAMPLING
13
repellent.. (It, corrodes aluminium very rapidly however.) An important
extension of the pitfall principle is due to Williams (1959) who has devised a clock-driven version which changes the receptacle into which
the animals fall a t regular intervals; this permits the use of these traps
for studies of diurnal activity rhythm.
Baited traps have not been widely used in small soil arthropod work
but the interesting results obtained by Walker (1957), who consistently
attracted characteristic species to fish, melon and cornflour baits show
that they have considerable potentialities. The principle is that of the
lobster pot and the structural details are probably not of great significance. The use of meat and fish for catching larger arthropods is discussed by Heydemann.
Obviously the main weakness of all the above methods is that they
are not applicable to absolute number estimates and that the catch
depends on the activity and behaviour of the animals. Activity is highly
dependent on weather conditions and the influence of behaviour is
revealed by the finding that many species are never caught in this way
whilst there are others hardly ever seen except in such traps, especially
those which are baited. However an extended trapping of this kind is
particularly useful under expedition conditions for obtaining a good
range of species in certain groups, especially beetles, and can be carried
on with a minimum of labour and materials.
2. LaboratoryA pparatus for the Treatment of Samples Removed froin the Soil
Although removal of soil to the laboratory has drawbacks such as the
alterations caused thereby to the habitat and the possibility of losses
and changes in the fauna there appears to be no quantitative method of
.sampling which avoids these objections. The details of soil core removal
naturally vary somewhat with the medium ; for instance in hard tropical
soils heavy machinery may be needed (Belfield, 1956) whilst sampling of
woodland litter may preclude the use of a core sampler of any kind and
demand the use of devices such as scissors and carpenter’s chisels to cut
a niass of material which will fit a tray as nearly as possible (Macfadyen,
1961). Naturally such factors have repercussions on the extraction
method used. A large number of core samplers has been described
(Coile, 1936; Alexander and Jackson, 1955; Macfadyen, 1953, 1961;
O’Connor, 1957). The most usual design consists of a hardened outer
cylinder containing one or more removable plastic or metal rings and
fitted with a handle. The cutting edge is often made slightly smaller
in diameter than the rings and these rest on a ledge some distance
above the cutting edge. This results in the loss of the deepest part of
the soil core, an unimportant matter in deep soils but a serious difficulty in shallow ones. In the latter case the author has obtained
13
repellent.. (It, corrodes aluminium very rapidly however.) An important
extension of the pitfall principle is due to Williams (1959) who has devised a clock-driven version which changes the receptacle into which
the animals fall a t regular intervals; this permits the use of these traps
for studies of diurnal activity rhythm.
Baited traps have not been widely used in small soil arthropod work
but the interesting results obtained by Walker (1957), who consistently
attracted characteristic species to fish, melon and cornflour baits show
that they have considerable potentialities. The principle is that of the
lobster pot and the structural details are probably not of great significance. The use of meat and fish for catching larger arthropods is discussed by Heydemann.
Obviously the main weakness of all the above methods is that they
are not applicable to absolute number estimates and that the catch
depends on the activity and behaviour of the animals. Activity is highly
dependent on weather conditions and the influence of behaviour is
revealed by the finding that many species are never caught in this way
whilst there are others hardly ever seen except in such traps, especially
those which are baited. However an extended trapping of this kind is
particularly useful under expedition conditions for obtaining a good
range of species in certain groups, especially beetles, and can be carried
on with a minimum of labour and materials.
2. LaboratoryA pparatus for the Treatment of Samples Removed froin the Soil
Although removal of soil to the laboratory has drawbacks such as the
alterations caused thereby to the habitat and the possibility of losses
and changes in the fauna there appears to be no quantitative method of
.sampling which avoids these objections. The details of soil core removal
naturally vary somewhat with the medium ; for instance in hard tropical
soils heavy machinery may be needed (Belfield, 1956) whilst sampling of
woodland litter may preclude the use of a core sampler of any kind and
demand the use of devices such as scissors and carpenter’s chisels to cut
a niass of material which will fit a tray as nearly as possible (Macfadyen,
1961). Naturally such factors have repercussions on the extraction
method used. A large number of core samplers has been described
(Coile, 1936; Alexander and Jackson, 1955; Macfadyen, 1953, 1961;
O’Connor, 1957). The most usual design consists of a hardened outer
cylinder containing one or more removable plastic or metal rings and
fitted with a handle. The cutting edge is often made slightly smaller
in diameter than the rings and these rest on a ledge some distance
above the cutting edge. This results in the loss of the deepest part of
the soil core, an unimportant matter in deep soils but a serious difficulty in shallow ones. In the latter case the author has obtained