Ever thought about taking up art to keep fit? What seems like a bizarre idea may help to answer the persistent riddle of why some spiders decorate their webs. A team in Germany believe that arachnid artwork may help to exercise the silk glands needed to wrap up prey.
Orb-weaver spiders also use their prey-wrapping silk to deposit conspicuous zigzag bands on their webs 鈥� a paradoxical behaviour for sit-and-wait predators that would probably be better off making their webs inconspicuous. Depending on who you listen to, the web decorations are for luring pattern-loving insects, attracting mates or preventing birds from accidentally flying into the web.
There is some evidence for all of these ideas, but only in some orb-weaver species and in certain situations. 鈥淭he significance of web decorations has been hotly debated for decades, and the jury is still out,鈥� says Andr茅 Walter at the University of Halle-Wittenberg in Germany.
Advertisement
Walter and his colleagues decided to look for an answer by comparing the webs woven by two groups of spiders. Both groups were fed the same diet but one group was allowed to wrap (but not eat) extra insects. These spiders were more likely to decorate their webs 鈥� one species in that group doubled the size of its ornaments. Walter says this can be explained if the excess silk production is needed to keep the glands ticking over and ready for action.
Orb-weaver spiders catch most of their prey during the day then rebuild their web and its decorations overnight. 鈥淲e think that the decorating might keep the silk glands active at a time when no prey is caught, to ensure they can make plenty of silk when it is needed for wrap-attacks later in the day,鈥� says Walter (Behavioral Ecology, ).
Todd Blackledge at the University of Akron in Ohio has previously shown that well-fed spiders decorate more. He reckons that decorations ward off potential web destroyers and predators. Blackledge says Walter鈥檚 work is fascinating but argues that the mere handling of extra prey might have stimulated the spiders to produce more decorations.
