I saw a Leafcutter slowly dragging herself forward over the debris near the nest.

She moved slowly, as if she had very bad arthritis.

The mystery became clear in a little while. Evidently the Leafcutter had been bitten by a male Euryopis spider.

He wrapped more silk around the ant, whose struggles had almost ceased at this point.

I must confess that I interfered, wanting a better photo of the spider's abdoment.

There was yet another Euryopis in a web over the entrance to the Leafcutter ant mound, this time a female. You can see here eating her prey here.

Sometimes an uninjured Leafcutter would climb up to the spider, as though the ant knew there was something wrong. She would bite at the spider's silk, trying to clear it away.

Often, she would come quite close to the spider. If the ant came too close, the spider would dart away without trying to bite. Maybe the spider needs to pick her envenomation sites with great care?

Euryopis would not run very far, usually only a couple of inches or so, then would be back to work on her meal some more.