I read here, here, and here that Painted Lady butterflies like to lay eggs on thistle, mallow or hollyhock. I found a picture of common mallow, which looked like the weeds growing on the edge of the compost pile, so I dug one up, planted it in a little pot, and placed the plant inside the butterfly habitat.
The next day, this is what we saw:
We released all but two of the butterflies today. They were absolutely lovely fluttering off into the sunny spring afternoon. The ladies and kindergarten gent all decided that they are interested in examining a butterfly but they most emphatically do not want to have to kill one. My sentiments exactly. We'll let the last two die a natural death, sometime in the next week, then look at them under the microscope.
We can't wait to see the caterpillars hatch. There's plenty more mallow over by the compost pile, and a couple thistles in the corner of the garden that I've declared protected caterpillar habitat. We'll release most of the caterpillars onto friendly host plants, and keep a few to feed and study so that we can watch the whole cycle all over again.
More about our Painted Lady butterfly garden here.
Nature journal sketches of the butterflies here.