140 Survey of Soil Fauna of Agricultural Land 



ranean and field strata to aerial stratum which takes place during the 

 summer months. Most species of soil-insects are hibernating in the larval 

 or pupal form and the other fauna experience a condition of diminished 

 activity. 



In order that a more exact idea might be obtained with regard to 

 the soil conditions, a mechanical analysis was carried out: 



Soil-samples of a standard size in lines across the field w^ere taken so 

 that representative samples might be obtained. The 9-inch cube sample 

 was used because 9 inches deep is usually the limit of habitable soil, few 

 species being found below that depth and at 9 inches the soil passes 

 into subsoil on most agricultural land. 



After taking the sample, the soil was spread out and allowed to dry 

 in the laboratory for two days. It was treated with three sieves of 

 \ inch, \ inch and 1 mm. While sifting, the soil both in the sieve and 

 that which had passed through was constantly examined for any speci- 

 mens. With practice two siftings are sufficient to detect all species, but 

 some dipterous larvae managed to pass the 1 mm. sieve. Little difficulty 

 was experienced by this method in noticing any specimens which feign- 

 ing death, remained still and harmonised with the soil, because the action 

 of the sifting seemed to bewilder and prevent them remaining motionless. 



The specimens were preserved in 5 per cent, formalin, but Dipterous 

 and Coleopterous larvae and pupae were previously boiled. Larvae and 

 pupae, especially those belonging to the Diptera, which could not be 

 immediately identified, were placed in breeding cages in order that the 

 adult form might be obtained. 



Special difficulties were encountered in samphng. It was found de- 

 sirable to let samples dry for a few days since their moist condition in 

 the fresh state prevented effective sifting. Owing to the clayey nature 

 of the Northenden soil it was impossible to take samples in wet weather 

 because the mechanical condition was such as to form hard clods impos- 

 sible to examine. 



