As usual, I was in Maine this year from late May through the end of the summer. In Maine late May is pretty much the beginning of butterfly season, and when I arrived it was unseasonably warm. So I immediately got out my net and went to see what I could find. What I found were some white butterflies which turned out to be Colias females. I assumed they were philodice, as they are much more common than eurytheme in the rural areas of Maine where I was. The interesting thing was that there were no yellow females flying with the white ones.
The white sulphurs petered out and the weather took a turn for the worse. It wasn’t till mid June that butterfly species began proliferating, including yellow sulphurs and cabbage whites. At this time, all the white butterflies I caught were cabbage whites. Any female Colias were yellow. Despite my best efforts, I couldn’t find another white Colias. I began to wonder about this.
Having lived in Maine most of my life, I had collected all the sulphurs and whites that seemed to be available (only three species of sulphur and two whites). I’d seen plenty of the white females, but had never noticed a time separation before. Now I wonder if I was missing something right in front of me. Or was 2015 just unusual? Or was it because I was only collecting in the small area near where I live?
Reading up on this subject from what is available on the internet, I learn that the alba female is more common in cooler areas, which certainly include inland Maine, and also that attention from whites (in Maine, primarily cabbage whites) and disfavor from yellow sulphur males are limiting factor in their reproduction. Maybe these factors explain the time difference I saw this year. Nevertheless, in 2016 I hope to spend more time looking into this.