September 20, 2012
Orb Weaver Spider Builds Intricate UV-Decorated Webs To Attract Insects
Lawrence LeBlond for redOrbit.com - Your Universe Online
The ultraviolet decorations and intricate patterns of the orb-weaver spider´s web is used to attract food, say scientists from the University of Incheon, whose studies of a common orb-weaver spider species are published in the journal Behavioral Ecology and Sociobiology.
Researchers suggest that the UV light-reflecting patterns seen in the webs of orb-weavers, particularly the Wasp Spider, could trick flying insects into landing on them. The Wasp Spider (Argiope bruennichi), which is common throughout Europe, north Africa and parts of Asia, is named for the females´ familiarly striped abdomens.
During web construction, these spiders are known to make zigzag patterns leading out from the center. The actual function of these complex patterns have been the subject of debate among the scientific community, with previous theories identifying them as scare tactics, signs of mating, sun shades and even camouflage.
But the South Korean researchers believe these UV-patterned webs are mainly for catching their food. And to test this theory, researchers compared decorated webs to webs without the unique patterns.
Professor Kim Kil-Won and colleagues studied the types of insects caught in each type of web, which revealed a possible clue to web decoration (known as stabilimentum) being the key in catching food.
Kim and his team found a link between the stabilimenta and increased foraging success for the spiders.
“The effects of stabilimenta on foraging success appear to be due to increased interception of UV-sensitive insect pollinators,” Kim told the BBC´s Ella Davies, adding that the UV-patterned webs caught twice as many large prey insects than the non-UV-patterned webs.
Kim said the pollinating insects, such as the 20 families of flies, wasps, beetles and butterflies caught in the stabilimenta, have greater visual sensitivity to UV light.
Previous studies have shown how these pollinating insects are attracted to flowers with high UV-reflectance and Kim suggested orb-weavers spin their webs to work in a similar manner, but instead capitalizing on attraction to secure a source of food.
Kim noted that stabilimentum probably also acts to “stabilize and strengthen the orb web,” which would likely be implemented to “maintain struggling large prey on the web.”
He also suggested the adaptation could be used in different ways by different species of orb-weaver spiders, but noted further study would be needed to understand their functions.