302 Insect and other Invertebrate Fauna 



It appeared possible that the introduction of insects, etc., in an 

 application of farmyard manure, and their subsequent death and decay 

 with gradual liberation of nitrogen, might account for the effects of an 

 application of farmyard manure being noticeable for a considerable time 

 afterwards. The quantity of nitrogen contained in the fauna seems, how- 

 ever, to be too small to be of great importance in this way, even although 

 the manured plot in this case had received farmyard manure annually 

 for 77 years. 



Although the bodies of the invertebrate fauna of the soil contain 

 quite an appreciable amount of nitrogen, there can scarcely be any loss 

 or gain of nitrogen due to them. The Oligochaeta, Myriapoda and other 

 groups which live and die in the soil, eventually return to it, at their 

 death, all they have taken from it. Although winged insects may leave 

 a plot in which their larvae have fed, this is probably balanced by other 

 insects migrating to the plot and dying there, whose larvae have fed 

 elsewhere, 



14. The Function of the Invertebeate Fauna in the Soil. 



Since the work of Darwin (i) and others (6), (14) the importance of the 

 earthworms in the soil has been widely recognised, the uniformity and 

 loose texture of the surface soil being attributed largely to them. By 

 means of their burrows air and water are enabled to penetrate the soil, 

 and their habit of drawing leaves, blades of grass and other vegetable 

 remains into their burrows adds to their importance. 



A considerable proportion of the damage done to land by floods is 

 considered to be due to the flooding out of the earthworms, so that the 

 surface soil remains compacted and vegetation languishes until a new 

 immigration of earthworms has restocked the soil. 



Some authors (3), (6), (7), (13) consider that, in addition to the mechanical 

 work of loosening the soil and assisting aeration and drainage, the earth- 

 worms, by the passage of considerable quantities of soil through their 

 bodies, render the mineral substances more readily available for plants. 

 On the other hand, the results of other experiments have tended to 

 disprove this theory (12). 



It has also been stated that by following the burrows of earthworms, 

 the roots of plants are able to penetrate to a greater depth than would 

 otherwise be the case, although this is denied by other workers (2). 



The work of insects, insect larvae and other invertebrates in the soil 

 is probably similar to that of the earthworms (7) in assisting in the 



