THE SOIL FAUNA: ANTHROPODS - The Soil - page 61

Some very small genera, such as Suctobelba and Minunthozetes , are very com-
pact and obviously adapted to getting about in the confined spaces of the fermentation
layer within leaf litter or within the soil itself. A few species have legs that are longer
than the body which makes them look more spider-like ( Plate 1 ) . In Damaeus onustus ,
for example, the front two pairs are directed forwards and the hind two pairs back-
wards so that, although the body is only 1.5mm long, the overall span of the legs is
nearly 4mm. This helps it to walk over the rough surface of a woodland floor, car-
peted with obstacles.
Oribatid mites shows two types of development very much as in insects. In
the 'lower' families, the young stages increasingly resemble the adults, as they do
in grasshoppers; in the 'advanced' families the nymphs are quite different from the
adult, and there is a marked metamorphosis as occurs in moths, beetles and flies,
though without the special pupal stage. A hundred years ago, careful observations
showed that the legs of the adult were folded under the body or sides and not formed
within the nymphal legs.
The young stages are vulnerable to predation and desiccation, and often live in
fungi or plant litter; pine needles, gorse twigs and leaf stalks which have lain on the
ground for some time are often riddled with oribatid nymphs ( Fig. 21 ). The duration
of life cycles varies greatly, from as little as five weeks to over a year for different
species, and there may be one to five generations a year.
The two other major groups of soil mites are the Mesostigmata and Prostigmata
in which the breathing pores are situated roughly midway along the sides or near the
base of the mouthparts respectively. The Mesostigmata are largely predatory. They
include those white or chestnut-brown, fast-running mites that can usually be seen
when a sod of grass or handful of garden compost is sieved over a tray. The legs are
often long and slender, and there is a pair of extrusible mouthparts with scissor-like,
toothed jaws at the tip. Their prey consists of springtails, insect eggs, nematodes and
other small creatures appropriate to their size. Figure 21 shows a springtail-eye view
of such a gamasid mite approaching. Like the oribatids, this group is most abundant
in the litter and uppermost soil layers but a few small mites, such as Rhodacarus spe-
cies, are more common a few centimetres down in the soil.