While out fossil hunting today I happened upon this gal. While it doesn't look it from this angle, from above it looks just like a Carpenter Ant. It moves along slowly and purposefully like any other ant, except this is a spider.
Members of the genus Castianeira are considered mimics of large ants, such as carpenter ants, and mutillid wasps, which are known as “velvet ants.” These spiders purposely walk about slowly the way ants do and then only move fast when disturbed. Many times they even raise their front two legs to mimic ant antennae.
These spiders mimic ants for several reasons. Many birds or predators that rely on sight to hunt, don't hunt ants because they are typically distasteful or aggressive. Ant mimics may also use their camouflage to hunt ants. A wolf in sheep's clothing!
Raynox DCR-250 mounted on my Panasonic FZ8.