Red Admiral and Dame's Rocket

While strolling in the Carleton College arboretum, Erika and I found this Red Admiral butterfly atop a Dame's Rocket.  The flower is escaped from cultivation.  This mustard was brought to North America from Europe in the 1700s.  Dame's Rockets have but four petals, unlike the five of phlox.

The butterfly is holarctic, which means that it is found in the Old and New Worlds in both northern hemispheres.  In much of the Red Admiral's range, this butterfly is migratory in the spring, and perhaps also in the fall.  In North America this species overwinters from south Texas through Guatemala.