152 Insect Fauna of Permanent Pasture 



Phygadeuon variabilis Grav. Reared from Dipterous (probably Tachinid) pupae. 



Hemiteles tristator Grav. Has been bred from Pieris brassicae and Limneria cocoons 

 among the eggs of Epeira diademata, Fumea intermediella and Solenobia triquetrella. 



The Braconid Aspilota nervosa Hal. is stated to be parasitic on Homalomyia 

 (Fannia) canicidaris. 



A nest of Vespa germanica Fab. occurred on the bank of one of the ponds on the 

 west of the field, and individuals from this and other nests in the neighbourhood were 

 frequently met with in the field. 



A number of burrows of Andrena cineraria L. occurred in a colony on a small 

 smooth area of bare soil between two of the ponds. These burrows were found in the 

 autumn to contain larvae, adults of both sexes, and other larvae which probably 

 belonged to a parasitic species of Nomada, these bees having been seen in the neigh- 

 bourhood of the burrows during the summer. 



10. Distribution in Depth. 



Relatively few insects, and those all in the larval state, were found 

 at a greater depth than two inches, and none deeper than six inches. 



This may be partly due to the fact that the soil was very compact 

 owing to the field having been a permanent pasture for many years. The 

 grass roots, although they formed a solid turf at the surface, did not 

 descend to any depth, as the predominant grasses of the field were 

 shallow-rooted species, and although there was a certain amount of 

 organic matter below the two inch level, there was very little below the 

 six inch level. Even when the ground was covered with three or four 

 inches of snow the insects did not appear to have descended to any 

 greater depth than usual, and when, during a period of hard frost the 

 ground was frozen to a deptb of about four inches, it did not appear to 

 cause any change in the depth to which the insects penetrated. 



The latter depth in any given area is probably controlled by four 

 factors: depth to which their particular food occurs, aeration, moisture 

 and temperature of the soil. In the present instance the food of both 

 carnivorous and vegetarian forms depended ultimately on the presence 

 of organic matter, either living plants or their decaying remams, this 

 material, as has been noted above, only being present, except in a very 

 small proportion, in the upper six inches, and particularly in the upper 

 two inches. 



Owing to the soil not having been disturbed for a considerable time, 

 it had become very much compressed, and consequently the aeration of 

 the soil would be poor, and again, owing to the very stiff subsoil, the 

 rain was not able to drain away readily, in some parts of the field even 

 forming pools on the surface. 



