Friday, July 10, 2009

Trickster spiders fool predators with their web-design

Spiders of the Cyclosa genus of spiders are, scientists has found, proficient web-designers. They pick up the carcasses of dead insects, bits of plant material and egg sacs and decorate their webs with them. Spider-biologists Ling Tseng and I-Min Tso from Tunghai University in Taichung, Taiwan wanted to know what purpose this curious behaviour served. Like the spider trickster-god Anansi, these spiders are masters of trickery.

Thinking that it was probably a way for the spider to camouflage itself the spiderologists compared how often Cyclosa spiders (of the confusa species) were attacked with decorated webs and with undecorated webs. Decorations-as-camouflage was not an unreasonable hypothesis, camouflage is a common trick to not get eaten and the decorations were similarly colored to the spiders. Nevertheless they were wrong. Decorated webs were attacked by predatory wasps more often than the undecorated ones. The spiderologists figured that the conspicous webs still provided some kind of advantage to the spiders, like how some lizards sports an eye-catching tail that they drop to distract attacking predators.

To test this, the spiderologists went to Orchid Island off the coast of Taiwan to study another Cyclosa spider, the C. mulmeinensis. This spider assemble detritus into life-like decoys of itself, a habit that seems unique to this specific species. The decoys has the same size, color and general shape as the spiders themselves and to attacking wasps, at least, the decoys appear near-identical to real spiders.

When a spider's web was not fitted with the active anti-predator device, wasps always went straight for the spider. With decoy spiders more often avoided becoming wasp food, outweighing the cost of attracting the predators in the first place. The same goes for non-decoy-building spiders. And they don't even have to sacrifice a limb like the lizards do! Tricksters, indeed.

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