surfaces of the soil particles. Swimming forms are 

 necessarily very small ; often, they appear dwarfed 

 compared to the size they have been brought to in 

 cultures. Xematodes are somewhat less restricted in 

 their movements. They can distort the surface of the 

 water film by means of muscular movements, and 

 thereby bridge intervening air spaces to the next soil 

 particle. Amoeboid organisms and hypotrichous cili- 

 ates usually accommodate their shapes to irregulari- 

 ties of the solid surfaces over which they crawl and 

 can become larger in size but still remain in the water 

 tilm. The variety of micro-habitats in the soil accom- 

 modating the large number of species that occur in- 

 cludes spaces between surface litter, caverns walled 

 off by soil aggregates, root channels, fissures, and 

 pore spaces between individual soil particles. These 

 micro-habitats vary in size, temperature, and moisture 

 conditions (Birch and Clarke 1953). 



Most of the insects, as well as the myriapod and 

 arachnid groups that belong to geobiontic fauna, are 

 wingless or nearly so (Lawrence 1953) ; many spe- 

 cies are also eyeless. Special respiratory organs are 

 either absent, the animals relying on their general 

 body surface for gas exchange, or are more or less 

 primitive. Most soil animals must, therefore, live in 

 an environment saturated with moisture, and out of 

 direct sunlight. The springtails jump around by 

 means of a special springing apparatus. Millipedes 

 and centipedes, of course, have numerous legs. Many 

 of these animals feed on plant litter and fungus, but 

 the pseudoscorpions, spiders, some of the mites, and 

 centipedes are carnivorous. Most of these species are 

 annuals or have even shorter life-cycles. Favorable 

 soil moisture and food are most important in limiting 

 their numbers ; temperature and hydrogen-ion con- 

 centration are secondary factors. Differences in the 

 character of soil, whether sand or clay, does not ap- 

 pear to affect the size of populations greatly ; how- 

 ever, the amount of decaying humus present is im- 

 portant. In Denmark the biomass of soil organisms 

 decreases from oak to beech to spruce forests (Table 



TABLE 9 8 Numbers o( toll animals per 

 in three different communities. 



r,' (n 



'Pearse 1946 

 ^Salt et al 1948 

 'Strickland 1945 



'From 5 samples from 3 forest reserves, total individuali 

 = number per m^ 

 ♦Larvae classified with adults 



9-9), but there is an increase in number of individ- 

 uals in beech and spruce over the oaks, attributable 

 to increased numbers of mites and springtails, which 

 are so small that they do not greatly affect the bio- 

 mass. Springtails also increase in abundance from 

 oak to spruce to beech in the forests of Yugoslavia 

 (Stevanovic 1956). Biomasses of mites and spring- 

 tails in an English grassland area varied from less 

 than 0. 1 to 1 .4 g/m^ ; they were generally at peak dur- 



^>^c^iin]]3C^ a 



J^Mhi 



v<ss<:^$^ 



FIG. 9-6 Soil fauna, (a) 

 campodeid, (b) japygid. (c) 

 proturan, (d) symphylld, (e) 

 springtail, (f) centipede (from 

 Kevan 1955). 



Grassland, forests, and forest-edges 



