234 W. SAUNDERS ON THE OCCURRENCE OF 



food for its larvœ, and iu the West lays its eggs on the prickly ash or on the hop tree, or 

 with eqiTal readiness selects the herbaceous dictamnus, and occasionally the heavy-odored 

 garden Rue. 



Doubtless these different plants are distinguished by their odor. It is difficult to 

 imagine iu what other way an insect could be attracted to a plant brought from some dis- 

 tant shore, of which none of its ancestors have had any knowledge. That insects possess 

 the power of distinguishing and api)reciating odors is evident. The carrion beetle traces 

 out the decomposing substance wherever it may be placed on the surface, and butterflies, 

 moths, and other insects swarm around sweet exudations or deposits. It may be asked 

 how is it that the permanent migration of this insect northward has been so long delayed, 

 and what circumstances have brought about the result. There was no lack of food plants, 

 for the shrubs it now feeds on have been growing here for thoxasands of years ; neither is 

 there any marked change in the climate. The question as yet remains unanswered. In 

 one respect the instinct of this butterfly appears to be at favilt. It seems to be unable to 

 appreciate the difference in climate between the south and the north, and continues to 

 deposit eggs until quite late in the season, too late to admit of the larvœ maturing before 

 winter. Last year I found some eggs and newly hatched larvœ as late as September 

 2nd. Most of the larvœ hatched at this period did not attain much more than half 

 their growth before severe frost rendered them torpid, when they became the prey of a 

 species of Hemiptera which pierced them and sucked them almost dry. Several specimens 

 which were a few days older escaped attack and grew with unusual rapidity, attaining 

 sufficient growth to admit of their entering on the chrysalis state, in which condition this 

 insect liasses the winter. A similar fault is also observed in the common cabbage butter- 

 fly, Pieris rapae, a comparatively recent importation from the milder climate of England, 

 which continues to deposit eggs on the cabbage until cold weather i^uts an end to its 

 powers. 



Another of our large and handsome sjiecies is PapUio philenor, a butterfly which is 

 extremely rare in Canada, so much so that in the course of more than twenty-five years' 

 experience I have not met with a single example. Two or three specimens were taken in 

 the neighbourhood of Woodstock, Ont., many years ago, and a most remarkable occurrence 

 of this insect iu great abundance in West Flamborough, Ont., in 1858, is recorded by the 

 Rev. 0. J. S. Bethune, iu the " Canadian Naturalist and Geologist " for August of that year. 

 He says, " these butterflies appeared iu countless numbers about the lilac trees as long as 

 they continued in blossom and then suddenly disappeared. They lasted from the "Zth to 

 the 18th of June, but very few appearing after that date." He also states that they were 

 numerous at that time about Toronto. There is no record of any similar occurrence of 

 this insect during the twenty-five years which have since passed. It is not an uncommon 

 butterfly in Ohio, and this flock may have come across Lake Erie, but it is most unusual 

 to find any butterfly so plentiful during the first brood, as to admit of flocks like this 

 traA'elling so far from their usual breeding grounds. The larva of philenor feeds on differ- 

 ent species of Aristolochia, none of which I believe are native to Ontario. Aristolochia sipho, 

 known, as Dutchman's Pipe, is cultivated as an ornamental climber in some gardens, but 

 whether there were any growing at that time in the vicinity of Flamborough is not known. 

 Had its natural food-plants been abundant, the sudden appearance of such a host would 

 prokably have resulted iu the species becoming a common one throughout western Ontario. 



