A few days ago, I was cleaning a garden bed, when I spotted a large butterfly fluttering around my herbs (photo above). It was extremely sunny and the little critter just paused for a short while, so I shot several photos hoping to get it in the frame:
Needless to say, the photos have poor definition, but I was able to identify it as an Eastern Black Swallowtail (Papilio polyxenes); they are not uncommon in my garden, but I thought it was a little late for an adult to be around. I checked about this species, and it happens to be non-migratory. For bird and butterfly lovers all over the North American subcontinent, migration is the quintessential theme right now; many species have begun their yearly journey from Canada and Northern USA to warmer sites in Southern USA and Mexico. One of the most studied migrating species is the Monarch Butterfly (Danaus plexippus); its migration pattern might seem to be in violation of any logic, since it is completed over four generations, and yet the butterflies follow the exact same rubric of locations and routes as their predecessors. This wonder of Nature continues to awe both entomologists and general public alike; in Mexico, The Monarch Butterfly Biosphere Reserve is a UNESCO World Heritage site.
The Black Swallowtail looks like a strong butterfly, and at least as large as the Monarch, so I wondered why they would choose to go into pupal stage and overwinter inside a chrysalis in Canada, instead of flying South like their cousins. I read this article explaining that migration is a mechanism triggered both by habitat conditions (such as overpopulation) and seasonal changes (like drop in temperatures), and that specific conditions generate different behavioural traits for different species, even when they are closely related. The article concludes with the observation that some migratory birds are already becoming sedentary, responding to local changes in temperature patterns, and due to urbanization.
I still thought it was kind of late to see an adult Black Swallowtail; should not the last summer generation of caterpillars be getting ready for the pupal stage by now? I was sad to ponder whether the gift of seeing this lovely butterfly so late in the season was a sign of global warming and too much urban development; I just hope we do not start spotting Monarchs in the fall around Southern Ontario.