Female Whirlabout, Polites vibex.
Image: Biosparite. [larger view]
The photographer writes: I encountered this species of grass skipper earlier this afternoon in the West 11th St. Park. It is nectaring at volunteers of Cut & Come Again Zinnias reseeding from 2006. One good way to have a butterfly garden on the cheap is to sow a lot of zinnia seeds.
Any idea as to the reason for the name 'whirlabout'?
I suspect the common name is derived from the way it flies ("Adult flight is quick and darting": see "Butterflies and Moths of North America" site maintained by Montana State University/Big Sky Institute).