On brome grass leaves growing from the margin of a mound of Formica obscuripes ants http://bugguide.net/node/view/265064. It was being examined by individual ants, but not swarmed over as one would imagine a prey item would be. Considering the 1,000's of ants inches away, it apparently didn't seem like food to them. It finally flew off weakly, a foot or so, perhaps because of my camera in its face, rather than the ants. Comments about their life cycle on Bug Guide's species info page suggest their larvae may live in F. obscuripes mounds. Also, a foot away from this beetle, there was an individual Sexton beetle, Nicrophorus marginatus http://bugguide.net/node/view/272621 What was its attraction to the ants?