Formica accreta, Northern California

I wish I could say I knew what these ants were doing.  Hiding from the photographer, perhaps?  Formica of the fusca species group are notoriously shy insects, but not all of these ones seemed to be equally spooked.

photo details: Canon MP-E 65mm 1-5x  macro lens on a Canon D60.
f/13, 1/200 sec, ISO 100
Twin flash diffused through tracing paper.
Levels adjusted in Photoshop.