Sipping nectar; taking flight.
The few milkweeds I planted in my "wild meadow" garden two decades ago have gradually spread until there are clumps of plants in every sunny location that I let alone. I allow their spread in hopes of attracting monarch butterflies, which depend on milkweed exclusively for food, but I have long been disappointed: butterflies come singly, sip a little nectar, and go. Days sometimes pass between visits. Last year we briefly had several monarch caterpillars! But they disappeared after I was forced to relocate them to milkweeds that did not hang dangerously over the driveway.
Thanks to John McCullough (https://www.flickr.com/photos/cup_prof/243098342/).
Today I wondered at a monarch visiting a plant past flowering. It would land on a leaf for only a second or two, then fly to another plant--I assumed, searching for flowers. But I happened to be watching at just the right moment from only twenty feet away: as she held on for just a moment, her abdomen curled around to the underside of the leaf. In a second or two she was gone. I dropped what I was doing and went to the leaf to find a single pale yellow sphere not much bigger than a period stuck to its underside! An egg, of course! She was "ovipositing!" Now that I knew what they looked like, and that the eggs were laid singly on the undersides of leaves, I was able to do a quick survey. Of the dozen milkweed plants I looked at, a fair fraction had eggs on them, sometimes several. I'll survey more plants tomorrow.
I found the eggs easier to spot with the sun shining almost parallel to the leaf surface.