Great idea for a thread...and great list.
For years now, when my early goldenrod begins to bloom, I know summer vacation. Is dwindling.
How wonderful that you've had hundreds of eastern tiger swallowtails! Sorry the numbers are dropping, but I guess that goes with the season. I hope to start seeing larger numbers of butterflies here. My first meadow planting is two years old, my second is finishing up its first year. Each year, I plan to add more until I fill the area. Already in my small planting, I'm seeing a few butterflies visit. As my meadow, trees, bushes, and various host plants grow and fill in, I'm hoping to start seeing the numbers you describe!
Thanks for starting a cool thread I'm sure we will start adding to the list as things occur to us.