One day last week, I glanced out my office window - I work in a very urban area - and six or more of the butterflies were swirling around the blossoms of a flowering crabapple tree. I was even seeing red admirals flying through traffic on very busy Morse Road. Our Ohio Birds listserv was awash in comments about the proliferation of these butterflies, so much so that I was awaiting the appearance of one of the self-appointed listserv police, to make one of their bah humbug "those aren't birds!" comments.
Dave Horn, an entomologist and current president of the Ohio Lepidopterists, made the following statement on our Ohio Birds listserv in response to all of the red admiral reports: " The red admiral has periodically appeared in large numbers since the early 19th century. While there is no universally accepted explanation for these increases it seems most likely that they are related to high overwintering survivorship in the southern USA followed by favorable conditions for northward movement. This year we have had both a very mild winter (in Ohio and southward) and an early spring and I suspect the large numbers we are seeing reflect those weather conditions".
Sums it up nicely, I think.
Not a bad strategy, if you can evolve yourself into it. Most critters probably shun nettles, same as we do, and that includes potential caterpillar predators.
Plant some nettles in your yard and who knows, you might raise a crop of admirals. Or better yet, as I believe it is the Weedpicker who says, sneak into your neighbor's yard and plant them there - that's close enough to still enjoy the butterflies!