One thing you notice if you spend much time outdoors in the US is how many invasive species there are and how they've taken over so much space. These species are often dead spaces for native insects (which is one reason they are so invasive, not being held back as native plants are). Not only is this bad for butterflies, but also for other kinds of insects, and for species like birds that prey on the insects.

I've long thought we need to be more aggressive at bringing in biological controls of these invasives. There's a tendency to be conservative about this, to not make mistakes, to study not act, but I think increasing risks have to be taken there because the existing situation is also a huge risk.

At the same time, I enjoy planting native plants in my garden. One of my favorite discoveries there was Pearly Everlasting (Anaphalis margaritacea), a low plant with pale blue-green leaves. When I first planted it, it was absolutely covered with caterpillars of the American (Painted) Lady butterfly. They ate down to bare stalks that then died. I thought it was done but it came back strongly and seeded enough to spread the next year. I think it's evolved to survive this sort of brutal spring pruning. I've since seen it in the wild, which was a treat.