260 [September, 



suffered in certaiu directions by serving as a source of food to pheasants, 

 etc. ; for example, the gamekeeper at Ravensworth has pointed out to 

 me the almost complete absence of ants in the woodlands there, these 

 serving as food to game ; just as lately, Mr. Spiller has recorded the 

 disappearance of Argynnis adippe L. from one spot in the Chilterns^^) ; 

 on the other hand, this destruction of ants may actually lead to the 

 preservation of other species, as there is no doubt that foraging ants 

 cause the destruction of enormous quantities of insect life, especially 

 in the larval stage.^^) 



As regards the last cause which is often brought forward for the 

 local disappearance of a species — that is over-collecting — it probably 

 applies only to the Lepidoptera, and naturalists in the north are not 

 so numerous that they have done very much harm here. Among the 

 other orders, the insects are usvially so difficult to find or to catch and 

 collectors are so few and far between that insect life is not affected in 

 the least. The only northern example T have come across is a state- 

 ment on good authority that Dytiscus marginali.<f L. vanished from the 

 neighbourhood of a certain uortliern town (not Newcastle), owing to 

 the necessities of biological study. 



Conclusion. 



To sum up, then, it seems probable that the most potent hvman 

 causes in the destruction of animal life are building operations, close 

 grazing, clean agriculture and forestry, destruction of woodlands, 

 heaths, commons, etc., and destriiction of plant life by smoke, dust, 

 and fumes ; the most potent human factor in its preservation is the 

 establishment of preserves where conditions are like those of primaeval 

 nature ; and then, besides this, there is apparently some power of 

 adaptation of at least certain species of insect life which enables them 

 to survive under most unnatural conditions. 



In conclusion, may I point out that if we desii-e to gain any real 

 insight into the sometimes obscure causes which determine the ex- 

 tinction or unusual abundance of insect species, it is necessary to make 

 a systematic survey of the species of a given restricted area, say of a 

 vice-county or even of a smaller district. This survey should embrace 

 a list of as many orders as possible with their relative numbers each 

 year, so as to show the relation, if any, between the abundance of one 

 species and the scarcity of another ; it should also contain an account 



(1) H. Rowland-Brown, "Butterflies of the Bucks. Chilterns," Entomologist, 1915, p. 120. 



(2) c/. G. B. Oliver on Araschnia levana, Entomologist, 1915, p. 63. 



