164 INSECT PESTS 



Th e burrows of earthworms penetrate 3 or 4 feet down 

 into the soil in mild cUmates, and as much as 6 or 8 

 feet in cold northern latitudes. It is in the constant 

 penetration of subsoil in this way that the great value 

 of the earthworm's service to mankind consists, as they 

 line such burrows with their casts, the latter being the 

 swallowed and digested soil and other matter on which 

 they Hve. These casts form valuable manure, although 

 the gardener sometimes eyes them askance when they 

 appear on a mild moist morning all over his lawn. Worm 

 casts occur throughout the world, even on the tops of 

 high mountains, such as in the Himalayas, where they 

 sometimes attain great size, 3 or 4 inches in height. 



The general result of this constant activity of earth- 

 worms, besides aerating, draining and fertihzing the 

 surface mould of the globe, is in addition to change the 

 face of nature, slowly and imperceptibly it is true, but 

 the process is always going on. Great stones left on the 

 top of the ground slowly subside and eventually disappear. 

 This is due to the bringing up of soil from underneath 

 by worms. It has been calculated that this burjdng 

 action may proceed at the rate of a quarter of an inch 

 a year, so it will readily be seen that although this 

 may seem very little in one season, in the course of time 

 vast changes must be made. Ancient monuments such as 

 Stonehenge and other druidical circles must eventually be 

 completely covered in by this agency. 



Worms give great aid to the denudation process carried 

 on by rivers and rain water running down hillsides, as 

 the soil is softened and rendered friable, so that it is 

 more easily carried away to fulfil the purpose of nature 

 in forming eventual new landscape elsewhere. The dark 

 colour of soil is entirely due to worms, who, hke most 

 animals, are provided with a digestive fluid which is 

 something akin to hydrochloric acid. The earth from 

 the subsoil level, when swallowed, becomes disintegrated 

 and changed from a bare mineral to a partially organic 



