Scientists Discover Why Orb-Weaving Spiders Build Silk Crosses on Webs
Posted on May 31, 2011
A team of scientists, led by Dr Andre Walter and Professor Mark Elgar from the University of Melbourne's Department of Zoology, have discovered how orb-weaving spiders protect their webs from damage. The orb-weaving spiders respond to severe damage to their spider webs by building bigger silk crosses. However, if damage to their webs is only mild the spiders do not build bigger silk crosses.
By building the more visible silk crosses the spiders are trying to make their webs more visible to larger animals, so they won't walk into them or fly through them. Professor Mark Elgar said web damage is costly for spiders as a lot of nutritional resources are required to rebuild a web. He says, "They they evolved this ingenious way to minimise unwanted damage. It's much like we mark glass windows with tape to prevent people walking into them."
The team tested the theory in the lab. They collected a group of orb weavers and let them construct webs. Then they severely damaged and lightly damaged some of the webs. They also left some of the webs untoutched.
Professor Elgan says, "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."