Spiders that spin orbed webs run the risk that low-flying birds will take out their hard-built structures. This may explain why some spiders weave conspicuous patterns into the centers of their webs - patterns whose function has puzzled biologists.
Thomas Eisner and Stephen Nowicki of Cornell University say they have demonstrated this notion experimentally. They report in Science that birds do indeed veer off to avoid well-marked webs while flying through other webs. They note that the markings, clearly visible to humans, probably also help larger animals avoid sticky entanglement.