226 



THE CANADIAN SPORTSMAN AND NATURALIST. 



in others is now almost exhausted is particu- 

 larly worthy of attention, whatever its value. 

 We know that innumerable species have be- 

 come extinct in past ages, and have been 

 followed by those which now furnish our 

 collectors with their favorite occupation. We 

 further know that within the memory of man 

 many species, as for instance among birds the 

 great auk and the dodo, have vanished, while 

 others are even now crossing the threshold. 

 Variations in climatic conditions, with conse- 

 quent alteration of habitats, must account for 

 the vast majority of changes in the terrestrial 

 fauna. What percentage, if any, can be as- 

 cribed to an inherent lack of specific vitality 

 appears to be a problem offering but little 

 prospect of solution. Not beingalepidopiterist 

 I can merely offer a suggestion, or rather I will 

 put a few queries, as to the sterility of the 

 autumn-emerging females of the Sphingkhe., a 

 characteristic of some of our own species as 

 well as of the European ones mentioned. Can 

 we consider these autumn specimens as imma- 

 ture individuals, which, under exceptional 

 conditions, attain the perfect form without a 

 corresponding perfection of the generative 

 organs? Had they the necessary vitality and 

 ability 10 exist during the winter, and until the 

 spring individuals (sexually mature) emerge, 

 would the ova become developed? Does the 

 appearance of such specimens after a hot and 

 prolonged summer indicate descent from 

 species which in more southern localities, or 

 under different conditions of temperature in 

 their present range, were double-brooded ? A 

 writer in "Science Gossip" some time ago 

 recorded the occurence in North India of 

 species which are also taken in England, and 

 stated that species which are single-brooded in 

 the latter place are double-brooded in India, 

 and also appear in great and often astonishing 

 abundance. Among them is Sphinx convol- 

 vuli, which apparently is only a visitant of the 

 British Isles, where it appears to be incapable 

 of continuing the species owing to unfavorable 

 climatic conditions. The last point brought 

 forward in Mr. Bowles' instructive paper is the 

 tendency of imported insects to supplant in 

 some instances our native species and to cause 

 them to become rarer. This is often due to 

 the energetic measures taken to suppress the 

 new comers, and which tend equally to thin 

 out the native species which, although they 

 have similar habits, are not so prolific or des- 

 tructive as to rouse agriculturists to take up 

 arms against them. The precautions taken 



against Pieris rapes are equally effective against 

 Pieris oleraeea, and have doubtless tendered 

 to its decrease rn the districts invaded by the 

 foreigner. 



W. Hague Harrington. 

 Ottawa, 5th April, 1883. 



CAUSES OF RARITY IN SOME SPECIES 

 OF INSECTS. 



I have been much interested in an article by 

 (t. J. Bowles in The Canadian Sportsman and 

 Naturalist for March, 1883, bearing the above 

 title and although I can offer little towards the 

 elucidation of the subject, yet I may attempt a 

 few suggestions and facts which may not be 

 uninteresting. For a convenience and pur- 

 pose, I class them under the following heads : — 



I. Drainage and cultivation. 

 '2. Variations of seasons'. 



3. Migrations. 



4. Holding over. 



5. Occasional visitants. 



1. The drainage and cultivation of land by 

 destroying or causing a scarcity in the natural 

 food plant or plants of any particular insect 

 must of necessity make the species rare in that 

 district, ultimately leading to their extinction, 

 but on the other hand, cultivation may have 

 the effect not only of producing other species 

 in that district, but of almost changing its 

 fauna. This according to Mr. Bowles' state- 

 ment, is now in progress in the Gromin swamp 

 near Quebec, in the case of C. jutfa, and the 

 same effect is remarkable in the Lincolnshire 

 and Cambridgeshire feus (England). In Yax- 

 ley fen and Whittlesea mere, where some 

 years ago, Papilio machaon used to be taken 

 in abundance and Zenzera arundinis com- 

 monly, but through the drainage and cultiva- 

 tion of the fens, those insects are now becom- 

 ing scarce, while Chrysophanes virgaurea and 

 C. dispar have completely died out. On the 

 other hand, cultivation and drainage have 

 changed the fen flora, producing an insect 

 fauna entirely dissimilar to their predecessors. 



2. Climatic influences on the variations of 

 seasons no doub have a very ^reat deal to do 

 with the relative scarcity or abundance of 

 insects, not so much, I am inclined to think, 

 as to the warmth or coolness of the previous 

 summer, as to the duration and regularity of 

 the winter temperature. In seasons when the 

 ground is covered with snow (as in the past 

 winter) and as a consequence the temperature 



