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"Do spiders have a mind?"

03.08.13

 

In a typical experiment, a choice of two paths is created with kinked coat hanger wire. The set-up simulates a pair of branches growing out of the forest floor and crossing over each other in a visually confusing way. Dangling at the end of each wire branch is an identical prey-holding dish. Into one is placed a dead spider (preserved and spray-coated to remove any odour cues). To make this bait jiggle attractively, it is jolted with a magnetic coil contraption.

A Portia that has been starved a few days is then released onto a platform in the middle of the maze – actually a tall wooden dowel that gives a view across the whole apparatus. To get to the dangling bait, the Portia has to work out which wire branch to take. The arrangement is such that once down on the ground, and even while climbing back across the wires, the spider is beneath the level of the dishes and so must rely on its memory of where it should be heading.

As a maze to be worked out from a single viewing – and with no previous experience of such mazes – this would be a tall order even for a rat or monkey. Yet more often than not, Portia could identify the right path. There was nothing quick about it. Portia would sit on top of the dowel for up to an hour, twisting to and fro as it appeared to track its eyes across the various possible routes.

(...)

Harland says it seems that Portia can see where it has to get to in order to start its journey and ignore distractions along the way. This impression was strengthened by the fact that on trials where Portia made a wrong choice, it often gave up on reaching the first high bend of the wire – even though the bait was not yet in sight. It was as if Portia knew where it should be in the apparatus and could tell straight away when it had made a dumb mistake.

(...)

In another experiment to explore its ability to learn, Portia was stranded on an island in the middle of a water filled tray. The distance was far enough that Portia had to decide whether to leap as far as it could or just swim. On some trials, the experimenters would make waves to push Portia back. On others they would help wash Portia to the other side. Portia would remember what had happened on the first trial and either make the same choice again if it had been successful, or switch tactics if it had been frustrated. Again this seems a rather dynamic, unprogrammed, response for such a small brain.

 

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