While taking pictures of Messor pergandei near their nest, my wife noticed a M. pergandei that looked as though it had climbed up on a weed and was holding on to it. Having just read Parasite Rex, we both immediately thought of the fluke that "takes control" of ants at a certain stage and makes them climb to a prominent place. This makes it more likely that that the ant will get ingested by the fluke's next host.
After watching the nest for a while, though, we saw an apparently dead ant moving across the nest. It turned out that a small spider was dragging the dead(?) ant off of the midden. The ant was attached to the spider by the spinnerettes. In the photos at the right, you can see a male spider next to the head of the Messor pergandei. The Extrafloral Nectary web site had photos of a similar spider - Euryopis.
After seeing the first spider and its victims, we began to notice more evidence of their activities at other nests. The vegetation around some nests looked like a scene out of Apocalypse Now, with Messor pergandei corpses swaying in the breeze.

Euryopis sp., next page