"What one perceives is ... the spider being in two places at the same time, i.e., in the cage, and eight feet accross the room." (O'Brien, 1997)
It is believed that this is actually a very subtle and sophisticated
predator-defense
mechanism of Old World spiders which appear to be capable of. Because they have co-evolved with Old World
primates, that may
prey on them, they may be pre-adapted to interfacing with the
neural pathways and
cognitive processes which mediate subjective visual
perception in humans (which are also basically Old World primates). Thus, their ability to project the transubstantiated corporeal gestalt of their physicality onto the mind of arachnoculturists, placing them in various apparent locations at once, the risk of pseudo-perception (or lack of a precise ability to localize the phenomenon we so jauntily call "tarantula") may lead to
escapes.
You should be warned that if too many of these spiders escape in your home and aggregate in seclusion, and thus join together into a group mind, forming a mental-matrix, all reality will fly out the window as the group of "tarantulas" practice transcorporeal
projection 'appearing' here, then there, at will. This could be an explanation of why these spiders tend to occur in colonies, in the wild. Their aggregate mind is a formidable
weapon. It is also easy to imagine that this could explain how arachnophobia could have had an
evolutionary basis for humans.
Imagine, if you will, early
anthropoids on the savannahs of east
Africa foraging for plump baboon spiders with pointed, fire-hardened sticks, digging at burrows in the hard soil. Suddenly, they see a spider here, then there in the hundreds, stridulating and clicking their fangs. The early hominoid troupe flees in terror!
It could be also true a function of the
horn of certain Harpactirinae. It acts as a suprasensory
antennae to better project the image of themselves away from what we so carelessly call their 'true' location. Please also note that these horns are situated just above the sub- and supra-esophageal ganglion, which is the central
nervous system of the spider. Furthermore, these horned species occur in arid scrub land habitats in regions of Africa where
baboons (Papio anubis) are common. Baboons of course consider these large spiders to be a tasty treat and eat them eagerly. So, we have an agent of natural selection. An evolutionary smoking gun, as it were. Because of large the size to their horn, Ceratogyrus cornuatum may be the most dangerous of all in this regard.