Male Diana fritillary butterfly on World Peace Wetland Prairie today. I wasn't quick enough to photograph him, but he is likely lurking near the Peace Circle still and maybe I'll photograph him nectaring or resting later: On june 21, 2010, I made a series of photos of one here and a few were decent closeups available on Flickr. Link below

Diana fritillary male from June 21, 2010,  on Aubunique Flickr site.
Comments from an authoritative source:
Habitat for the Diana fritillary includes the edges and openings in moist, rich mountain forests. They will also use pastures, shrublands, and fields for nectaring but will only breed if there is a suitable forest margin. Larval hostplants are various species of violets (Viola sp.)
There is one flight from June to September. Males emerge before females and patrol within the forest. Females lay eggs later in the flight period, mainly August, walking along the ground and attaching eggs singly to twigs and dead leaves. As with other Speyeria species, the caterpillars hatch and hibernate without feeding. They emerge in spring to feed on the leaves and flowers of various species of violets.
Adults feed on nectar from a variety of plants, including milkweeds (Asclepias sp.), ironweed (Vernonia sp.), and red clover (Trifolium pratense). Males will also drink fluids from dung.