Scientists crack the spiders' web code

May 31, 2011
Scientists crack the spiders' web code

( -- Decorative white silk crosses are an ingenious tactic used by orb-weaving spiders to protect their webs from damage, a new study from the University of Melbourne has revealed.

The team, led by Dr. Andre Walter and Professor Mark Elgar from the University of Melbourne’s Department of Zoology, found that orb-weaving respond to severe damage to their webs by building bigger silk crosses, but if the damage is mild they don’t bother adding extra decoration.

Professor Mark Elgar said web damage is costly for spiders as a lot of nutritional resources are required to rebuild a web. “So they evolved this ingenious way to minimize unwanted damage,” he said.

“It’s much like we mark glass windows with tape to prevent people walking into them,” he said.

The team collected a group of orb-weaving spiders and left them to build their webs in the laboratory. Some of the completed webs were severely damaged, others lightly damaged and the remainder left alone. The response of the spiders was then observed.

“The fact that spiders increased their decorating activity in response to severe damage but didn’t increase their decorating following light suggests that the conspicuous building of silk crosses serves to make webs more visible to animals that might accidentally walk or fly into them,” Professor Elgar said.

Decorative white silk crosses are an ingenious tactic used by orb-weaving spiders to protect their webs from damage. Credit: Andre Walter

Adding decorations to spiders’ orb-webs was first reported over a century ago but why these spiders decorate their webs has been the topic of controversial debate for decades.
“Our study helps unravel this mystery,” Professor Elgar said.

The study was published in Behavioral Ecology and Sociobiology.

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5 / 5 (3) May 31, 2011
Nice article with an unrelated headline.
not rated yet May 31, 2011
Does increasing the decoration not increase the tensile strength of the web as well? Did they look at increasing strength? Why is it that adding decoration only increases visibility?
not rated yet May 31, 2011
...and isn't the whole point of a web that something flies accidentally into it?
not rated yet May 31, 2011
Yes Antialias, but I would think about visual scale. A small insect would see the cross if it was moving right toward it, but not if it was flying through an unmarked section. Where as a larger individual may be tipped off if they see the cross as a small part of their visible area.
Of course if it is full of crosses then, well its probably a bad area for a web in the first place.
Also yes moj85 I would assume the same thing.
not rated yet May 31, 2011
I seem to remember seeing an article some time ago that these web decorations were there to act as a visual warning to small birds to stop them flying through the webs and damaging them.
3 / 5 (2) May 31, 2011
Interpreting behavior from an underlying premise of visual cues is a bold suggestion. Whatever overlying premise is assumed, that premise probably entails anything preventing extinction.

So birds seeking meals via crosses is excluded.
Preposterous! Birds don't eat spiders.
5 / 5 (1) Jun 01, 2011
Decorative white silk crosses are an ingenious tactic used by orb-weaving spiders to protect their webs from damage
That's an anthropomorphizing and, worse, teleological interpretation. Actually they would have to measure the rates of captured insects in webs with and without silk cross out in the wild in order to draw conclusions like this.
a lot of nutritional resources are required to rebuild a web
Is this an assumption only or a scrutinized fact?
not rated yet Jun 01, 2011
Related article concerning the visibility of spider web decorations to predators and prey:
not rated yet Jun 01, 2011
Wasp spiders on the UK south coast build webs in tall grass where there are large populations of grasshoppers. They often include a single vertical web decoration which I have postulated is to simulate a grass blade and so encourage prey to make a mistaken leap into the web.

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