Scanning and route selection in the jumping spider Portia labiata.

Jumping spiders Portia labiata were tested in the laboratory on three different kinds of detours. In one, both routes led to the lure. In the other variants, one of the routes had a gap, making that route impassable. When tested with only one complete route, Portia chose this route after visually inspecting both routes. An analysis of scanning showed that, at the beginning of the scanning routine, the spiders scanned both the complete and the incomplete route but that, by the end of the scanning routine, they predominantly scanned only the complete route. Two rules seemed to govern their scanning: (1) they would continue turning in one direction when scanning away from the lure along horizontal features of the detour route; and (2) when the end of the horizontal feature being scanned was reached, they would change direction and turn back towards the lure. These rules 'channelled' the spiders' scanning on to the complete route, and they then overwhelmingly chose to head towards the route they had fixated most while scanning. Copyright 1999 The Association for the Study of Animal Behaviour.