ji3 The Ottawa Naturalist. [August 



plants disappear and are replaced by intruders from afar. The 

 primeval forest perishes ; its larger denizens are slaughtered or 

 driven away, and the plants and animals that remain are such 

 as can best adapt themselves to the changed conditions of the 



land. 



Many persons may recognize these self-assertive changes 



and still not stop to think that our insect fauna and evtn those 

 smaller forms of life that delight the microscopist are also 

 similarly affected by the far-spread improvements or disturb- 

 ances of the landscape. 



Yet a moment's consideration will suffice to show that such 

 is actually the result. An insect may be able to exist only upon 

 a single species of plant, and the destruction of that host-plant 

 involves the disappearance of its guest. Or, the actual change 

 in physical conditions may equally well bring about a change in 

 the insect life. The draining of a swamp and its gradual con- 

 version into dry woods or open fields necessitate the with- 

 drawal of those species which require a cold moist habitat, and 

 correspondingly tend to create conditions favourable for forms 

 from more southern localities. These changes go on steadily 

 year after year whether we notice them or not, and the destruc- 

 tion of the forest, the cultivation of the land, the pasturing of 

 flocks and herds, and ever expanding commerce accelerate the 

 alterations in insect population. Our indigenous insects are 

 supplanted by prolific and vigorous forms from lands where 

 evolution has fitted them to successfully overcome the disadvan- 

 tages of man's society and solicitudes. The species whose food 

 plants are destroyed, and which are unable to assimilate the new 

 order of vegetation, disappear, accompanied by many of their 

 parasitic and predatory associates. Replacing them come 

 insects from near or afar, especially those thoroughly domesti- 

 cated forms which follow man wherever he pitches his tent or 

 builds his shack. 



In a discussion of the insect population as it now appears 

 to our collectors, a difficulty arises at the start in our inability^ 

 in many instances, to distinguish between the descendants of the 





