It’s been a banner year for butterflies here in the Upper Delaware River Valley, according to my neighbors and friends. Resident butterfly buffs have noticed an uptick in monarch (Danaus plexippus) populations this season. As well, anecdotal accounts of a local population boom in Eastern tiger swallowtails (Papilio glaucus) are echoed in reports of an explosion of the species all along the east coast this year.

I saw many tiger swallowtails this summer flying with monarchs around my milkweed plants. Some days there were at least 10 or more at a time of the dramatic, yellow and black stripped butterflies sipping nectar from the sticky, purple milkweed blooms. It was a butterfly banquet.

According to the website www.ecosystemgardening.com, these butterflies normally peak in April/May (which is probably why I associate them with lilac time) and again in July/August. Perhaps what we were all seeing was a normal peak in population. However, the website also suggests that the surge in population may have been due to the unusually cold spring we had this year, which may have suppressed the parasites and viral infections which normally shrink population size.

Also this summer, I saw my first giant swallowtail (Papilio cresphontes) locally. A relative to the tiger swallowtail, the giant swallowtail is known as the largest butterfly in North America. While it is mainly known as a southern species, I have heard of a few sightings in the area this summer.

My friend Becky Nevin-Gales was lucky enough to get a photo of a giant swallowtail not far from Long Eddy. Later on, I went back to see if I could find it too. I did see the butterfly gliding among the patches of goldenrod along Nevin Road. We followed in an exciting chase for a while in Becky’s car but after a few changes of direction (which required backing up the car and multipoint turns) we gave up.

While its main food plant is sweet orange and other citrus crops, the giant swallowtail eats a variety of plants including prickly ash (Zanthoxylum americium) which is found locally.

The giant swallowtail’s range reaches as far north as southern Canada and as far south as Venezuela while also extending into southern California. It is most common in the Deep South.

According to my cousin, Robert Dirig, giant swallowtails have successfully overwintered as pupa in the Ithaca, NY, area for about the past 10 years or so. And, while there have been reports of sightings of the butterfly in New York for about 150 years, in recent years there has been an increase in incidences along the butterfly’s northern range. It appears that an absence of frosts in early fall might have led the larva to adapt to endure cooler temperatures. Or, perhaps, warmer temperatures have affected host plant growth or decreased parasites, according to an article from The Journal of the Lepidopterists’ Society.

The verdict is still out as to whether we can chalk this expansion up to climate change or not. There do seem to be many factors at work to change butterfly range.

Another butterfly treat this summer was my discovery of a monarch caterpillar chrysalis in the wild. I have only seen one other in my life. This caterpillar was found in J formation on a pumpkin vine in my garden. The next day it had transformed into a gem of a chrysalis. We are still watching and waiting for the butterfly to emerge.