St. Andrew's Cross spider (By Andre Walter)
Have you ever walked through the woods or even a doorway and received a face full of spider web? It鈥檚 not a pleasant experience. The invisible threads of the web stick to your skin and because they鈥檙e incredibly thin and delicate, removal doesn鈥檛 happen nearly as fast as you鈥檇 like.
While a -esque sign of 鈥淒anger!鈥 would be nice, the is a trap for unsuspecting insects, so it鈥檚 typically inconspicuous. Some orb web spiders, though, do something unusual: They decorate their webs. One of these spiders, the St. Andrew鈥檚 Cross spider, weaves thicker bands of zigzagging silk that form easily identifiable crosses. The crosses broadcast the location of the web as well as that of the spider, which sits in the web鈥檚 center. But what鈥檚 the purpose of the decorations since they seem to defeat the very definition of a trap?
The decorations tell animals the spiders don鈥檛 eat to 鈥淪tay Away!鈥 say researchers from the University of Melbourne. When unaware animals, such as mammals and birds, run into a web, its owner must spend both time and energy in reconstructing it. Spiders that need to rebuild lose opportunities to catch meals.
If its web is heavily damaged, then the St. Andrew鈥檚 Cross spider will make the crosses larger in the next round, found the recently published Behavioral Ecology and Sociobiology . Over the course of two weeks, the researchers caused damage to the webs of 44 spiders. In one group, they inflicted mild damage, which would be similar to the spider鈥檚 prey landing in the web. In the other group, the scientists made the webs collapse by cutting two crucial corner tethers. The group that sustained the heavy damage and had major remodeling to do made their future webs smaller with larger decorations than the group that sustained mild damage, which didn鈥檛 change its building habits.
In nature, decorated webs stay around longer than undecorated ones. Although the decorations may shoo non-prey animals away, scientists debate whether they also serve as advertisements to the spider鈥檚 own predators that flash 鈥淚鈥檓 here!鈥
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