154 Insect Fauna of Permanent Pasture 



This is possibly due, in the case of " Glover's Meadow," to the absence 

 of dung from the field, as that substance attracts many species, including 

 the species of Bibio, to which the high figure obtained in the present area 

 was partly due. With the "Alluvial Pasture," the difference may be due 

 to its tendency to be marshy throughout the year, which condition is 

 unfavourable to soil insects. 



12. Census of Soil Insects. 



During the investigation twenty-nine samples, each with a superficial 

 area of 100 square inches, were examined, and a total of 1658 insects 

 were obtained. From this figure the total number of insects in an acre 

 of the field works out at 3,586,088, which is probably somewhat below 

 the actual number, as with small insects like Collembola and Thysano- 

 ptera, it is difficult to be sure of securing every specimen, and a proportion 

 of the more active forms of the other families probably effect their 

 escape during the removal of the soil. 



The numbers of the different orders were: Collembola, 566,680; 

 Rhynchota, 15,140; Thysanoptera, 43,258; Lepidoptera, 15,140; Coleo- 

 ptera, 744,038; Diptera, 2,193,180; Hymenoptera, 8652. 



The figure for Diptera is considerably increased by the finding on 

 one occasion of 464 larvae in a sample, but about 50 larvae were not 

 infrequently met with in a sample of soil. 



Among notably injurious species the numbers per acre work out as 

 follows: Agriotes, larvae 114,634, adults 8652; larvae and pupae of Tri- 

 phaena pronuba L. 4326 ; larvae of Tipula oleracea and T. paludosa 19,466. 



The numbers of insects per acre found by Cameron, as calculated 

 from the figures he gives, are 835,560 for " Glover's Meadow," and 

 1,537,046 for the " Alluvial Pasture." M'Atee, working near Washington, 

 U.S.A., calculated that on an acre of forest floor there were 1,216,880 

 animals belonging to Insecta, Arachnida and other Arthropoda, Annelida 

 and Gastropoda ; similarly in an acre of meadow land in the same locality 

 he calculated that there were 13,654,710 animals. 



As this figure includes Arachnida and other Arthropoda, Annelida 

 and Gastropoda, it cannot be compared with the figure obtained in the 

 present instance. 



13. Summary. 



1. An area was chosen which was as typical as possible of the per- 

 manent pasture fields of the district, and in which invasion by insects 

 not belonging to the area would be reduced to a minimum. 



