Why would a monarch butterfly hang around a milkweed with no flowers?

 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.

I will watch in the days to come for the caterpillar that must be curled up in each egg.  I hope they survive the marauding of the many insects that pass by.  Those that do--even if they hatch immediately--will probably not be big enough to see for weeks.  But now I know they're there; and now I know where to look!