Orb weaving spiders choose to become more ornate – so some say.
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 spiders 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 minimise 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 damage 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.
A spider web, spiderweb, spider’s web or cobweb (from the obsolete word coppe, meaning “spider”) is a device built by a spider out of proteinaceous spider silk extruded from its spinnerets.
Spider webs have existed for at least 140 million years, as witnessed in a rare find of Early Cretaceous amber from Sussex, southern England.
Spiders originally started producing silk for reasons other than web-making. When spiders moved from the water to the land in the Early Devonian period, they started making silk to protect their bodies and their eggs. Spiders gradually started using silk for hunting purposes, first as guide lines and signal lines, then as ground or bush webs, and eventually as the aerial webs which are so famous today.
The “typical” orb-weaver spiders (family Araneidae) are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields and forests. Their common name is taken from the round shape of this typical web, and the taxon was formerly also referred to as the Orbiculariae.
Orb-weavers have eight similar eyes, legs hairy or spiny and no stridulating organs. The Araneidae family is cosmopolitan, including many well-known large or brightly colored garden spiders. There are 3,006 species in 168 genera worldwide, making Araneidae the third largest family of spiders known (behind Salticidae and Linyphiidae). The orb-weavers include over 10,000 species and make up about 25% of spider diversity.
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