Experiment of the month

Natural History, July-August, 2002 by Stephan Reebs

As one might expect, given its common name, the Australian jumping spider Portia fimbriata can leap. But somewhat surprisingly, this terrestrial arachnid doesn't mind swimming, either. Robert R. Jackson, of the University of Canterbury in New Zealand, and colleagues made use of the spider's aquatic talents in an experiment to determine how this animal would respond when presented with a problem it had never before encountered. The researchers marooned spiders, one at a time, on a tiny "island" in the middle of an "atoll" in a water-filled tray. The spiders could get closer to freedom (the edge of the tray, which the jumping spiders could clearly see with their acute vision) by first reaching the atoll. Some individuals attempted to do so by initially leaping, which generally got them midway to the atoll, and then swimming the rest of the way. Others swam from the start. The researchers used a scoop to make waves, helping some spiders reach the atoll while washing others back to the central is land. All those that made it to the atoll employed the same tactic they had used when leaving the island (whether that had been to leap first or to start out swimming) to finish their journey to the edge of the tray. In contrast, almost all the spiders that failed to reach the atoll the first time switched tactics the next time they attempted the trip from island to tray's edge--leaping if they had swum and swimming if they had leaped. Spiders in the genus Portia are known to employ trial-and-error tactics when hunting prey (other spiders), tapping out different signals on the web of an intended victim until they come up with one that induces the prey to expose itself. The current study shows that these spiders are able to apply problem-solving skills that probably evolved in one context--hunting--to another, unfamiliar context. ("Trial-and-Error Solving of a Confinement Problem by a Jumping Spider, Portia fimbriata," Behaviour 138, 2001)

Stephan Reebs is a professor of biology at the Universite de Moncton in New Brunswick, Canada, and the author of Fish Behavior in the Aquarium and in the Wild (Cornell University Press).