I believe this is the same individual...it flew when I attempted to approach more closely, and landed on the shore of the river about 40 feet away.

Note the black alula (=lobe at base of wing, on posterior edge)...given as a diagnostic character for M. terminalis in Torsten's online key.

The mostly red abdomen; otherwise black body; and smokey wings seem to give (at least preliminary) gestalt for this species (after one is already tipped-off to genus by the long, clubbed antennae; frontally-flattened head and blocky proboscis; unusual forwardly-curved wing venation...and the large size!).